Process for manufacturing a structure comprising a layer acting as a barrier against the diffusion of atomic species
A surface treatment using oxygen and nitrogen plasmas forms a nitrogen-rich barrier layer to prevent atomic species diffusion, thereby maintaining RF performance in structures with charge trap layers.
Patent Information
- Application Number
- JP2024577184
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-07-04
- Filing Date
- 2023-06-20
- Publication Date
- 2025-07-15
AI Technical Summary
Existing structures with charge trap layers are susceptible to degradation in RF performance due to the diffusion of atomic species like hydrogen and lithium, which solidify and dope the trap layer, leading to performance deterioration.
A method involving surface treatment with oxygen and nitrogen plasmas is applied to form a barrier layer on the exposed surfaces of the support and donor substrate, creating a nitrogen-rich layer that prevents the diffusion of these species.
The barrier layer effectively inhibits the diffusion of hydrogen and lithium, maintaining the RF performance of the structure by preventing these species from reaching the trap layer.
Smart Images
Figure 2025522620000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a method for manufacturing a structure comprising a thin layer transferred onto a support provided with a charge trap layer. The present invention is particularly useful in the fields of microelectronics, microsystems, photonics, etc.
Background Art
[0002] International Publication No. 2021008742 points out that it is often advantageous to provide a charge trap layer (more simply referred to as a "trap layer" in the remainder of this specification) in the support of a structure formed by a thin layer transferred onto a support via a dielectric layer. The manufacturing of this type of structure is disclosed, for example, in French Patent Nos. 2860341, 2933233, 2953640, US Patent Application Publication No. 2015115480, US Patent Nos. 7268060, and 6544656. In particular, the present invention can be used to form electronic components or electroacoustic components in the field of radio frequency (RF) signals.
[0003] Thin films, which are often single crystals, can be made of semiconductors (such as silicon) or insulators (such as piezoelectric materials such as lithium tantalate or lithium niobate).
[0004] The aforementioned documents also disclose the fact that this type of structure is particularly sensitive to hydrogen because this atomic species can diffuse and solidify in the trap layer, thereby tending to inactivate the electrical defects contained in this layer, and as a result, the RF performance of the structure deteriorates. As described in the January 2015 publication "White paper - RF SOI Characterisation" issued by SOITEC, the RF performance of the substrate can be characterized by measuring the second harmonic distortion.
[0005] The Applicant has also observed that when the thin film contains lithium, this atomic species also diffuses into the structure during its manufacturing steps, solidifies in the trap layer, and is likely to dope it. Similar to hydrogen, the presence of lithium in the trap layer tends to degrade the RF performance of the structure.
[0006] To prevent the degradation of RF performance caused by the diffusion of atomic species (especially hydrogen) in a structure having a trap layer, International Publication No. WO 2021 / 008742 proposes incorporating a diffusion barrier into the dielectric layer.
[0007] (Object of the Invention) One object of the present invention is to improve this prior art by proposing a very simple and effective method for incorporating a diffusion barrier against specific atomic species, especially hydrogen and / or lithium, in a structure including a charge trap layer.
Summary of the Invention
[0008] To achieve this object, the object of the present invention is to propose a method for manufacturing a structure including a thin layer transferred onto a support by a dielectric layer, the support including a charge trap layer disposed superficially on a base substrate, the method including the following steps. - Forming a dielectric layer on the exposed surface of the so-called "main" surface of the support and / or on the exposed surface of the so-called "main" surface of the donor substrate. - Applying a surface treatment to the exposed surface of the main surface of the support and / or to the exposed surface of the main surface of the donor substrate for the purpose of forming a layer acting as a barrier against the diffusion of specific atomic species thereon. - Assembling the support and the donor substrate by their respective main surfaces to form an intermediate structure. Removing at least a part of the donor substrate from the intermediate structure to form a thin layer.
[0009] The method is excellent in that the surface treatment applied to at least one of the exposed surfaces includes the following. - Exposing the exposed surface to a plasma containing oxygen to form a damaged thickness under the main surface. - Exposing the exposed surface to a plasma containing nitrogen to nitride the damaged thickness.
[0010] Such surface treatment simply forms a layer that acts as a barrier to the diffusion of specific atomic species, which is particularly effective against the diffusion of hydrogen and / or lithium. Therefore, this avoids causing a decrease in RF performance in the structure.
[0011] According to other advantageous non-limiting features of the present invention, alone or according to any technically feasible combination, it is as follows. - The donor substrate includes a single crystal piezoelectric material. - The donor substrate is a single crystal silicon substrate. - The base substrate is a single crystal silicon substrate. - The dielectric layer includes silicon oxide. - The trap layer is made of polycrystalline silicon. - The formation of the dielectric layer includes the oxidation of the trap layer. - The formation of the dielectric layer precedes the application of surface treatment to the exposed surface of the main surface of the support. - The dielectric layer follows the application of surface treatment to the exposed surface of the main surface of the support. - The silicon oxide dielectric layer incorporates nitrogen, preferably with a nitrogen / oxygen ratio of less than 0.5. - The formation of the dielectric layer includes the formation of at least a part of the dielectric layer on the donor substrate. - The application of surface treatment includes the application of surface treatment to the exposed surface of the main surface of the donor substrate. - The formation of at least a part of the dielectric layer on the donor substrate precedes the application of surface treatment.
Brief Description of the Drawings
[0012] Other features and advantages of the present invention will become apparent from the following detailed description of the present invention with reference to the accompanying drawings.
Figure 1
Figure 2
Figure 3
DETAILED DESCRIPTION OF THE INVENTION
[0013] Generally speaking, referring to FIG. 1, this description relates to a method for manufacturing a structure 1 that continuously includes a thin nanocrystalline layer 4, a dielectric layer 3, and a support 2. The support 2 itself includes a base substrate 2a provided with a charge trap layer 2b. Preferably, the dielectric layer 3 is in contact with the trap layer 2b and the thin layer 4. As described in the introductory part of this application, such a structure 1 is particularly suitable for accommodating radio frequency (RF) components on or in the thin film 4.
[0014] To prevent specific atomic species from diffusing towards the trap layer 2b, the structure 1 includes a barrier layer 5 disposed within the dielectric layer 3 on the structure 1 shown in FIG. 1. As will be described in the remainder of this disclosure, in addition to or instead of a barrier layer disposed in the dielectric layer, the barrier layer can be disposed superficially in or on the support 2 itself, or even on or in the thin layer 4 (on the side of the dielectric layer 3). The barrier layer has a thickness of about 5 nm, typically between 2 nm and 10 nm, and contains a large amount of nitrogen.
[0015] Atomic species that are likely to diffuse towards the trap layer 2b can originate particularly from the thin layer 4. This can be, for example, lithium 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 between the thin layer 4 and the trap layer 2b that can prevent the diffusion of lithium, a decrease in the RF performance of the structure 1 is avoided.
[0016] Atomic species can also arise from the dielectric layer 3. This is particularly true when this layer is produced by a deposition technique involving a moderate heat treatment of less than 1000 °C, at least in part. In these processes, certain species such as hydrogen species cannot diffuse out of the deposited layer, and thus these species are likely to diffuse towards the trap layer 2b during other steps in the manufacture of the structure 1. Here too, the presence of the barrier 5 prevents the diffusion of these species towards the trap layer 2b, and degradation of the RF performance of the structure 1 is avoided.
[0017] Conventionally, the structure 1 can be in the form of a circular wafer, the diameter of which can be 100, 150, 200, 300, or even 450 mm.
[0018] The base substrate 2a of the support 2 on which the trap layer 2b is placed typically has a thickness of several hundred micrometers. Preferably, the base substrate 2a has a high resistivity of more than 1000 ohm - centimeters, and even more preferably, more than 2000 ohm - centimeters. This limits the density of charges, holes, or electrons attempting to move within the base substrate. However, the present invention is not limited to a base substrate 2a having such a resistivity, and the RF performance advantages are also provided when the base substrate has a more compatible resistivity of about several hundred ohm - centimeters, for example, less than 1000 ohm cm, or less than 500 ohm cm, or even less than 10 ohm cm.
[0019] For reasons of chirality and cost, the base substrate 2a is preferably made of single-crystalline silicon. It can be, for example, a CZ silicon substrate having a low inter-lattice oxygen content of 6 to 10 ppm, or in particular, an FZ silicon substrate having a naturally very low inter-lattice oxygen content. Also, it can be a CZ silicon substrate having a large amount of inter-lattice oxygen (represented by the expression "high Oi") exceeding 26 ppm. The base substrate 2a can alternatively be formed from another material, for example, it can be sapphire, glass, quartz, silicon carbide, etc. In certain situations, especially when the trap layer 2b is sufficiently thick, for example, with a thickness exceeding 30 microns, the base substrate 2a can have a standard resistivity of less than 1 kΩ·cm.
[0020] As described in the literature forming the prior art, the properties of the trap layer 2b can be quite diverse. Generally, it is, for example, a polycrystalline layer having structural defects such as dislocations, grain boundaries, amorphous zones, voids, inclusions, pores, etc. These structural defects form traps for charges that tend to circulate in the material, for example, in incomplete or undetermined chemical bonds. This prevents conduction in the trap layer, and as a result, the trap layer has a high resistivity.
[0021] Advantageously, for ease of implementation, this trap layer 2b is formed of a layer of polycrystalline silicon. This layer can be formed by deposition on the base substrate 2a. Its thickness can be configured to be 0.1 to 3 μm, especially when formed on the resistive base substrate 2a. However, other thicknesses below or above this range are also fully conceivable depending on the level of RF performance expected from the structure 1.
[0022] In order to maintain the polycrystalline nature of this layer during the heat treatment applicable to the structure 1, for example, an amorphous layer made of silicon dioxide can be advantageously provided on the base substrate 2a before the deposition of the trap layer 2b.
[0023] Alternatively, the trap layer 2b can be formed by implanting relatively heavy species such as argon into the surface thickness of the base substrate 2a in order to form structural defects that constitute electrical traps therein. This 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, and these structural defects can trap charges.
[0024] The dielectric layer 3 is preferably made of silicon oxide. Other chemical elements can also be incorporated into this layer, either in trace amounts or at higher concentrations. Specifically, this layer can incorporate nitrogen (to form a SiON layer), for example, at a nitrogen / oxygen ratio of less than 0.5. To characterize the proportion of nitrogen in the layer, measured values of its refractive index, which vary between 1.44 for SiO2 and 2.35 for Si3N4 (at a wavelength of 620 nm), are used.
[0025] The thin layer 4 of the structure 1 can be of any suitable type. If the structure 1 is intended to receive an integrated semiconductor component, the thin layer 4 can be composed of single-crystalline silicon or any other single-crystalline semiconductor material such as germanium, silicon germanium, silicon carbide, etc. If the structure 1 is intended to receive a surface acoustic wave filter, the thin layer 4 can be composed of a single-crystalline piezoelectric material such as lithium tantalate or lithium niobate and / or a ferroelectric material. The thin layer 4 can also include a finished or semi-finished integrated component that is formed on a donor substrate and transferred onto the support 2 during the steps of manufacturing the structure 1. Generally, the thin layer can be from 10 nm to 10 microns thick.
[0026] As presented in the documents forming the state of the art presented in the preamble, the structure 1 can be manufactured in many ways. Very generally, referring to FIG. 2, the structure 1 can be fabricated by a manufacturing method including the following. - Providing a support and a donor substrate. -Forming a dielectric layer on the exposed surface of the so-called "main" surface of the support and / or on the exposed surface of the so-called "main" surface of the donor substrate. -Applying a surface treatment to the exposed surface of the main surface of the support and / or the exposed surface of the main surface of the donor substrate for the purpose of forming a barrier layer thereon. -Assembling the support and the donor substrate by their respective main surfaces to form an intermediate structure. -Removing a part of the donor substrate from the intermediate structure to form a thin layer 4 placed on the support by the dielectric layer.
[0027] The dielectric layer can be produced, for example, by deposition using LPCVD (low-pressure chemical vapor deposition) or PECVD (plasma chemical vapor deposition) techniques. This can also be an HDP CVD (high-density plasma chemical vapor deposition) technique.
[0028] The silicon oxide dielectric layer 3 can be obtained by oxidizing the donor substrate when the donor substrate is made of silicon, or by oxidizing the trap layer 2 when the trap layer 2 is also made of silicon. In this second case, after oxidation, a polishing step on the oxidized surface is performed to facilitate the subsequent assembly of the donor substrate and the support substrate 2.
[0029] The assembly step is preferably carried out by molecular adhesion. As is well known per se, during the molecular adhesion method, the exposed surfaces of the support and the donor substrate, which are completely clean, flat, and smooth, are brought into close contact with each other to promote the formation of, for example, van der Waals type or covalent type molecular bonds. Then, the two bodies are assembled without using an adhesive. These bonds can be strengthened by applying a heat treatment to the intermediate structure.
[0030] The step of removing a part of the donor substrate can be carried out by chemically and mechanically thinning this substrate. Preferably, the structure 1 is manufactured by applying Smart Cut™ technology, according to which the layer intended to form the thin layer 4 is delimited by a weakened plane formed by the implantation of light species (typically hydrogen and / or helium) into the donor substrate. After the assembling step, this layer is removed from the donor substrate by breaking along the weakened plane and is thus transferred to the support 2.
[0031] Next, the steps included in the surface treatment intended to easily form the barrier layer 5 in the structure 1 during manufacturing will be described in detail.
[0032] As seen, this surface treatment is applied to the exposed surface of the main face of the support and / or the exposed surface of the main face of the donor substrate.
[0033] If a dielectric layer is pre-formed on the main face of one of these two elements by deposition or oxidation, the exposed surface to which the surface treatment is applied thus corresponds to the exposed surface of the dielectric layer. However, quite generally, the surface treatment can be applied to either or both of the donor substrate and the support, regardless of whether they have a dielectric surface layer or not.
[0034] The surface treatment can be applied to the exposed surface of the support and / or the donor substrate before the dielectric layer is deposited on this face.
[0035] Therefore, to avoid ambiguity, it is specified that the surface treatment resulting in the formation of the barrier layer 5 can be applied to the donor substrate only, to the support only, or to both of these substrates. The formation of the dielectric layer can precede or follow the application of the surface treatment.
[0036] Regardless of whether the surface treatment is performed on one or both of these two substrates, the surface treatment consists of two consecutive sub-steps, as shown in Figure 3. In the first sub-step, the exposed surface is exposed to a plasma containing oxygen. This first sub-step results in the formation of a thin, porous (or more generally) damaged layer with a thickness of about 5 nm (typically 2 nm to 10 nm) on or embedded just beneath the surface. The plasma to which the substrate surface is exposed in this first step can be an oxygen plasma, or an oxygen plasma combined with a gas having the general formula C x H y F z such as sulfur hexafluoride (SF6).
[0037] In the second sub-step following the first sub-step, the exposed surface of the treated substrate is exposed to a plasma containing 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 can consist of nitrogen.
[0038] It is not necessary to perform these two steps in-situ, and it is possible to expose the donor substrate or support to the atmosphere between the first sub-step and the second sub-step.
[0039] The plasma exposure sub-step can consist of placing the substrate in a chamber of a plasma activation device, for example, on a planar support disposed within the chamber, and exposing the main surface to the plasma prepared by a source. An oxygen-based (first sub-step) or nitrogen-based (second sub-step) flow is introduced into the plasma source of the device at a controlled flow rate, and the plasma of this gas is generated, for example, by a variable magnetic field or a variable electric field. The plasma species are ejected onto the exposed surface. These operations can be performed at atmospheric pressure or under reduced pressure.
[0040] This series of sub-steps makes it very easy to produce a relatively thin barrier of about 5 nanometers that incorporates a large amount of nitrogen, making it particularly effective. Specifically, this barrier is even more effective in preventing the diffusion of specific atomic species compared to a barrier formed only by exposure to a single nitrogen plasma.
[0041] Naturally, the present invention is not limited to the described embodiments, and variant embodiments can be added thereto without departing from the scope of the present invention defined by the claims.
Claims
1. A method for manufacturing a structure (1) including a thin layer (4) transferred onto a support (2) including a charge trap layer (2b) disposed superficially on a base substrate (2a) via a dielectric layer (3), the method comprising: - forming a dielectric layer (3) on the exposed surface of the so-called "main" surface of the support and / or on the exposed surface of the so-called "main" surface of a donor substrate; - applying a surface treatment to the exposed surface of the main surface of the support and / or the exposed surface of the main surface of the donor substrate for the purpose of forming a layer acting as a barrier against the diffusion of specific atomic species thereon; - assembling the support and the donor substrate by their respective main surfaces to form an intermediate structure; - removing at least a part of the donor substrate from the intermediate structure to form the thin layer, wherein the method is characterized in that the surface treatment applied to at least one of the exposed surfaces - exposes the exposed surface to a plasma containing oxygen to form a damaged thickness under the main surface; - exposes the exposed surface to a plasma containing nitrogen to nitride the damaged thickness.
2. The manufacturing method according to claim 1, wherein the donor substrate includes a single crystal piezoelectric material.
3. The manufacturing method according to claim 1, wherein the donor substrate is a single crystal silicon substrate.
4. The manufacturing method according to any one of claims 1 to 3, wherein the base substrate (2a) is a single crystal silicon substrate.
5. The manufacturing method according to any one of claims 1 to 4, wherein the dielectric layer (3) includes silicon oxide.
6. The manufacturing method according to any one of claims 1 to 5, wherein the trap layer (2b) is polycrystalline silicon.
7. The manufacturing method according to any one of claims 1 to 6, wherein the formation of the dielectric layer (3) includes the oxidation of the trap layer (2b).
8. The manufacturing method according to any one of claims 1 to 7, wherein the formation of the dielectric layer (3) precedes the application of the surface treatment to the exposed surface of the main surface of the support (2).
9. The manufacturing method according to claim 7, wherein the formation of the dielectric layer (3) follows the application of the surface treatment to the exposed surface of the main surface of the support (2).
10. The method of manufacturing according to claim 5, wherein the silicon oxide dielectric layer incorporates nitrogen, preferably with a nitrogen / oxygen ratio of less than 0.
5.
11. The method of manufacturing according to any one of claims 1 to 10, wherein the formation of the dielectric layer (3) includes forming at least a part of the dielectric layer on the donor substrate.
12. The method of manufacturing according to any one of claims 1 to 11, wherein the application of the surface treatment includes applying the surface treatment to the exposed surface of the main surface of the donor substrate.
13. The method of manufacturing according to any one of claims 1 to 12, wherein the formation of at least a part of the dielectric layer (3) on the donor substrate precedes the application of the surface treatment.