A lithium niobate modulating device and a method for manufacturing the same

Abstract

The application provides a lithium niobate modulation device and a preparation method thereof, and relates to the technical field of electro-optical modulation devices.The preparation method of the lithium niobate modulation device comprises the following steps: forming metal deposition grooves on both sides of a waveguide structure of a waveguide substrate, respectively, and depositing metal electrodes in the metal deposition grooves; filling metal protection medium in the metal deposition grooves to completely cover the metal electrodes by the metal protection medium; and bonding a lithium niobate substrate to the waveguide substrate after forming the metal electrodes to obtain the lithium niobate modulation device.The application prepares a metal electrode deposition groove in the form of etching a silicon oxide slot, and prepares a metal electrode structure in the metal electrode deposition groove, thereby optimizing the defects of the incompatibility between the CMOS process and the preparation of the metal electrode after the heterogeneous integration of the lithium niobate substrate and the waveguide substrate, avoiding the preparation of the waveguide structure at low temperature, reducing the optical loss of the waveguide structure, and improving the performance of the lithium niobate modulation device.

Description

Technical Field

[0001] The present invention relates to the technical field of electro-optical modulation devices, and in particular to a lithium niobate modulation device and a preparation method thereof. Background Art

[0002] The silicon photonics platform enables dense integration of photonic components and systems, as well as electronic circuit integration. Its advantages, such as low power consumption and low cost, have led to its widespread application in fields such as optical communications and gyroscopes. Electro-optical modulators, which convert electrical signals into optical signals, play a crucial role in these fields, transmitting electronic signals to optical carriers. With the rise of commercial integrated photonics, a variety of modulation platforms have been demonstrated to be compatible with wafer-level manufacturing. Among them, lithium niobate (LNbO3) has garnered widespread attention due to its excellent electro-optical modulation performance.

[0003] The currently commonly used technical solution is to use bonding and other processes to perform heterogeneous integration of lithium niobate substrates and waveguide substrates. The metal electrodes are mainly distributed in two locations, above or below the lithium niobate substrate: (1) The metal electrode is located above the lithium niobate substrate. This solution uses W2W (wafer to wafer) bonding. After the bonding is completed, the silicon substrate above the lithium niobate substrate is removed, and then the metal is grown and patterned. (2) The metal electrode is located below the lithium niobate substrate. This solution first prepares the metal electrode, then prepares the waveguide layer to form the waveguide substrate, and then heterogeneously integrates it with the lithium niobate substrate.

[0004] In the above solution (1), metal electrodes need to be grown after bonding the lithium niobate substrate. Since lithium niobate materials will pollute the thin film growth chamber, it is difficult to be compatible with CMOS processes and cannot be applied on a large scale. In the above solution (2), since the metal electrodes are prepared first and then the waveguide materials are grown and patterned to form the waveguide structure, the metal electrodes cannot withstand high temperatures. The waveguide materials need to be prepared using plasma enhanced chemical vapor deposition (PECVD) technology. The waveguide materials grown at low temperatures (such as silicon nitride) have poor density and large optical loss. In addition, the distance between the electrode material and the waveguide material prepared in this solution is large, resulting in poor electrical performance. Summary of the Invention

[0005] In view of this, an embodiment of the present application provides a lithium niobate modulation device and a preparation method thereof. The embodiment of the present application achieves compatibility with CMOS process while avoiding low-temperature preparation of waveguide structure and reducing the optical loss of the device by cutting grooves and growing metal electrodes in the grooves.

[0006] The present application provides the following technical solution: a method for preparing a lithium niobate modulation device, comprising:

[0007] Forming metal deposition grooves on both sides of the waveguide structure of the waveguide substrate, and depositing metal electrodes in the metal deposition grooves;

[0008] Filling the metal deposition tank with a metal protection medium so as to completely cover the metal electrode with the metal protection medium;

[0009] A lithium niobate substrate is bonded to the waveguide substrate after the metal electrode is formed to obtain the lithium niobate modulation device.

[0010] According to one embodiment of the present application, the method further includes: forming a first silicon oxide layer on a silicon substrate, forming a patterned waveguide structure on the first silicon oxide layer, and covering the waveguide structure with a second silicon oxide layer to obtain the waveguide substrate.

[0011] According to an embodiment of the present application, the waveguide structure includes a first waveguide structure layer and a second waveguide structure layer sequentially located on the first silicon oxide layer.

[0012] According to an embodiment of the present application, the first silicon oxide layer is prepared by thermal oxidation, and the second silicon oxide layer is prepared by chemical vapor deposition.

[0013] According to one embodiment of the present application, the method further includes: filling the metal deposition tank with a metal protective medium, and allowing the metal protective medium to completely fill the gaps in the metal deposition tank, and flattening the surface of the metal protective medium at the mouth of the metal deposition tank and the surface of the waveguide substrate through chemical mechanical polishing.

[0014] According to an embodiment of the present application, the metal protection medium is a silicon oxide film.

[0015] According to one embodiment of the present application, the bottom of the metal deposition tank extends into the first silicon oxide layer, and the depth of the metal deposition tank is greater than 1 μm.

[0016] According to one embodiment of the present application, the thickness of the metal electrode does not exceed the groove depth of the metal deposition groove, and the top of the metal electrode is not higher than the top of the waveguide structure.

[0017] According to one embodiment of the present application, the lithium niobate substrate includes a lithium niobate thin film layer, a third silicon oxide layer, and a silicon substrate sequentially located on the waveguide substrate.

[0018] The present application also provides a lithium niobate modulation device prepared by the above method.

[0019] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: the embodiment of the present invention first prepares metal deposition grooves on both sides of the waveguide structure of the waveguide substrate, and deposits metal electrodes in the metal deposition grooves; fills the metal deposition grooves with a metal protective medium to completely cover the metal electrodes with the metal protective medium; and finally bonds a lithium niobate substrate to the waveguide substrate after the metal electrodes are formed, thereby obtaining the lithium niobate modulation device. The embodiment of the present invention prepares metal deposition grooves by etching silicon oxide to form grooves, and prepares a metal electrode structure in the metal deposition grooves, thereby optimizing the defect of incompatibility with the CMOS process when preparing metal electrodes after heterogeneous integration of the lithium niobate substrate and the waveguide substrate; the metal electrode structure is prepared after the waveguide structure is prepared, which is compatible with the CMOS process and avoids preparing the waveguide structure at a low temperature, thereby reducing the optical loss of the waveguide structure and improving the performance of the modulation device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0021] Figure 1 This is a schematic flow chart of a method for preparing a lithium niobate modulation device according to an embodiment of the present invention;

[0022] Figure 2 This is a first schematic diagram of the preparation process of the lithium niobate modulation device in an embodiment of the present invention;

[0023] Figure 3 is a second schematic diagram of the preparation process of the lithium niobate modulation device according to an embodiment of the present invention;

[0024] Figure 4 is a third schematic diagram of the preparation process of the lithium niobate modulation device according to an embodiment of the present invention;

[0025] Figure 5 is a fourth schematic diagram of the preparation process of the lithium niobate modulation device according to an embodiment of the present invention;

[0026] Figure 6 is a fifth schematic diagram of the preparation process of the lithium niobate modulation device according to an embodiment of the present invention;

[0027] Among them, 10 and 20 are silicon substrates, 11 and 21 are silicon oxide layers prepared by thermal oxidation, 12 is a silicon-rich silicon nitride waveguide layer, 13 is a silicon nitride waveguide layer, 14 is a silicon oxide layer prepared by chemical vapor deposition, 15 is a metal deposition tank, 16 is a metal electrode, and 22 is a lithium niobate thin film layer. DETAILED DESCRIPTION

[0028] The embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0029] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0030] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing a lithium niobate modulation device, comprising:

[0031] 101. Forming metal deposition grooves on both sides of the waveguide structure of the waveguide substrate, and depositing metal electrodes in the metal deposition grooves;

[0032] 102. Filling the metal deposition tank with a metal protection medium so as to completely cover the metal electrode with the metal protection medium;

[0033] 103. Bonding a lithium niobate substrate onto the waveguide substrate after forming the metal electrode to obtain the lithium niobate modulation device.

[0034] The embodiment of the present invention prepares a metal electrode deposition groove by etching silicon oxide to form grooves, and prepares a metal electrode structure in the metal electrode deposition groove, thereby optimizing the defect of incompatibility with the CMOS process when preparing the metal electrode after the heterogeneous integration of the lithium niobate substrate and the waveguide substrate. The metal electrode structure is prepared after the waveguide structure is prepared, thereby solving the defects of large optical loss and poor performance of the waveguide structure. The embodiment of the present invention is compatible with the CMOS process, while avoiding the low-temperature preparation of the waveguide structure, reducing the optical loss of the device, and improving the performance of the lithium niobate modulation device.

[0035] In order to avoid low-temperature preparation of the waveguide structure, reduce the optical loss of the device, and improve the performance of the lithium niobate modulation device, in some embodiments of the present invention, the method also includes: first preparing a waveguide substrate; the process of preparing the waveguide substrate specifically includes: first forming a first silicon oxide layer from bottom to top on a silicon substrate, forming a patterned waveguide structure on the first silicon oxide layer, and covering the waveguide structure with a second silicon oxide layer to obtain the waveguide substrate.

[0036] In a specific implementation, the first silicon oxide layer is prepared by thermal oxidation, and the second silicon oxide layer is prepared by chemical vapor deposition. The two silicon oxide layers are non-isotropic thin-film structures, with a silicon nitride waveguide structure located between them. The first silicon oxide layer is prepared by thermal oxidation, which offers the best density and film quality. It can serve as the underlying silicon oxide layer for growing a high-quality silicon nitride film layer to optimize optical performance. After the silicon nitride film layer is grown, thermal oxidation is no longer feasible. Therefore, chemical vapor deposition is used to deposit the upper cladding silicon oxide layer, forming the second silicon oxide layer. While the film quality is slightly inferior to that of the first silicon oxide layer, it can serve as a cladding layer to protect the silicon nitride waveguide structure.

[0037] In a specific implementation, before etching to form the metal deposition groove, the surface of the second silicon oxide layer is subjected to chemical mechanical polishing to make the surface of the second silicon oxide layer smooth and flat, thereby precisely controlling the uniformity of the etching depth of the metal deposition groove.

[0038] In some embodiments of the present invention, the waveguide structure may be a double-layer waveguide, i.e., the waveguide structure includes a first waveguide structure layer and a second waveguide structure layer, patterned sequentially from bottom to top, on the first silicon oxide layer. In a specific implementation, the first waveguide structure layer may be a silicon-rich silicon nitride waveguide layer, and the second waveguide structure layer may be a silicon nitride waveguide layer.

[0039] In specific implementation, the thickness of the first silicon oxide layer is 3-8 μm, the thickness of the silicon nitride waveguide layer is 50-450 nm, and the thickness of the second silicon oxide layer is 500 nm-1 μm. The specific dimensions of the three are determined according to current design conditions and process windows.

[0040] To ensure compatibility with CMOS processes when fabricating metal electrodes after heterogeneous integration of a lithium niobate substrate and a waveguide substrate, while avoiding low-temperature fabrication of the waveguide structure and reducing device optical loss, some embodiments of the present invention further include: filling the metal deposition tank with a metal protective medium, ensuring that the metal protective medium completely fills the gaps within the metal deposition tank, and flattening the surface of the metal protective medium and the waveguide substrate at the opening of the metal deposition tank through chemical mechanical polishing. The surface formed by the metal protective medium and the waveguide substrate is flattened for subsequent bonding to the lithium niobate substrate.

[0041] In order to ensure compatibility with CMOS technology when preparing metal electrodes after heterogeneous integration of lithium niobate substrate and waveguide substrate, while avoiding low-temperature preparation of waveguide structure and reducing device optical loss, in some embodiments of the present invention, the metal protective medium adopts silicon oxide film.

[0042] In specific implementation, this embodiment uses plasma-enhanced chemical vapor deposition (PECVD) to prepare a silicon oxide film to fill the metal deposition groove and form a passivation layer on the metal electrode surface to protect the metal electrode: the silicon oxide film has a high resistivity and can effectively prevent current from flowing in an unwanted direction, thereby protecting the metal electrode; silicon oxide has good stability under most environmental conditions, is not easily susceptible to chemical corrosion and physical damage, and can resist the erosion of oxygen, moisture and other harmful substances in the air, thereby extending the service life of the metal electrode; silicon oxide can form a good interface with a variety of metals without causing obvious chemical reactions or interface defects. This compatibility allows silicon oxide to adhere tightly to the surface of the metal electrode, providing stable protection; in addition, the silicon oxide film prepared by PECVD technology has good etching groove filling properties, and will not introduce defects such as voids and gaps during the deep groove filling process. Therefore, silicon oxide films are often used as protective layers and passivation layers for devices in CMOS processes.

[0043] Because the metal electrode must have a certain thickness (~1 μm) to ensure good electrical performance, the metal deposition tank is etched to a depth greater than 1 μm, and the bottom of the metal deposition tank extends into the first silicon oxide layer. In some embodiments of the present invention, the thickness of the metal electrode does not exceed the depth of the metal deposition tank, and the top of the metal electrode does not exceed the top of the waveguide structure.

[0044] In some embodiments of the present invention, the metal deposition tank is located on both sides of the waveguide structure, and the bottom of the metal deposition tank extends into the first silicon oxide layer. In specific implementation, the metal electrode layer can be made of materials such as Al and Cu. The thickness of the metal electrode does not exceed the depth of the metal deposition tank, and the top of the metal electrode must not be higher than the top of the waveguide structure, with the gap controlled to be 0-100nm. The reason is that after the metal electrode structure is prepared, it needs to be covered with a metal protective dielectric layer, i.e., a silicon oxide film layer, and the second silicon oxide layer is subjected to a CMP process (chemical mechanical polishing) to control the second silicon oxide layer to be 100nm higher than the silicon nitride waveguide layer, thereby optimizing the optical performance and preparing for the subsequent bonding process. If the metal electrode is higher than the waveguide structure layer, there is not enough process window to control the silicon oxide thickness on the silicon nitride waveguide layer to be 100nm, thereby affecting the optical performance. It may also cause damage to the metal electrode during the CMP process, thereby affecting the electrical performance.

[0045] In specific implementation, the groove depth of the metal deposition groove is 1.5-2μm, which is determined by the final thickness of the second silicon oxide layer; the thickness of the metal electrode is 0.8-1μm, so that the top of the metal electrode is lower than the top of the silicon nitride waveguide structure to prevent subsequent CMP process and bonding process from causing damage to the electrode.

[0046] In some embodiments of the present invention, the lithium niobate substrate comprises a lithium niobate thin film layer, a third silicon oxide layer, and a silicon substrate sequentially disposed on the waveguide substrate. The third silicon oxide layer is prepared by thermal oxidation. This process provides the highest density and film quality, thereby optimizing optical performance.

[0047] like Figure 2-Figure 6 As shown, this embodiment proposes a solution of forming grooves and growing metal electrodes in the grooves. The following describes the process steps of the embodiment of the present invention in detail using a Si3N4 waveguide substrate as an example (all schematic diagrams are cross-sectional views unless otherwise specified):

[0048] First, prepare a silicon nitride waveguide substrate, such as Figure 2 As shown, the silicon nitride waveguide substrate includes the following steps: a silicon substrate 10, a silicon oxide layer 11 prepared by thermal oxidation, a silicon-rich silicon nitride waveguide layer 12, a silicon nitride waveguide layer 13, and a silicon oxide layer 14 prepared by chemical vapor deposition.

[0049] Secondly, the silicon oxide layer is etched on both sides of the silicon nitride waveguide to form a metal deposition groove 15 structure for subsequent preparation of metal electrodes in the metal deposition groove 15, such as Figure 3 As shown. Again, a metal electrode 16 is deposited in the metal deposition tank 15, as shown Figure 4 shown.

[0050] Next, a silicon oxide film is prepared to fill the metal deposition groove 15 to protect the metal electrode 16, and chemical mechanical polishing (CMP) is performed to form a smooth and flat surface for subsequent bonding, such as Figure 5 shown.

[0051] Finally, a lithium niobate substrate is prepared, and the lithium niobate substrate and the waveguide substrate are heterogeneously integrated using a bonding process, such as Figure 6 As shown, the lithium niobate substrate includes a silicon substrate 20, a silicon oxide layer 21 prepared by thermal oxidation, and a lithium niobate thin film layer 22.

[0052] In the embodiment of the present invention, a metal deposition groove is prepared by etching silicon oxide to form a groove, and a metal electrode structure is prepared in the metal deposition groove, thereby optimizing the defect of incompatibility with the CMOS process when preparing the metal electrode after the heterogeneous integration of the lithium niobate substrate and the waveguide substrate; the metal electrode structure is prepared after the waveguide structure is prepared, which is compatible with the CMOS process and avoids the low-temperature preparation of the waveguide structure, thereby reducing the optical loss of the waveguide structure and improving the performance of the modulation device.

[0053] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for preparing a lithium niobate modulation device, characterized in that: include: Forming metal deposition grooves on both sides of the waveguide structure of the waveguide substrate, and depositing metal electrodes in the metal deposition grooves; Filling the metal deposition tank with a metal protection medium so as to completely cover the metal electrode with the metal protection medium; A lithium niobate substrate is bonded to the waveguide substrate after the metal electrode is formed to obtain the lithium niobate modulation device.

2. The method for preparing a lithium niobate modulation device according to claim 1, wherein: The method further includes: forming a first silicon oxide layer on the silicon substrate, forming the patterned waveguide structure on the first silicon oxide layer, and covering the waveguide structure with a second silicon oxide layer to obtain the waveguide substrate.

3. The method for preparing a lithium niobate modulation device according to claim 2, wherein: The waveguide structure includes a first waveguide structure layer and a second waveguide structure layer sequentially located on the first silicon oxide layer.

4. The method for preparing a lithium niobate modulation device according to claim 2, wherein: The first silicon oxide layer is prepared by thermal oxidation, and the second silicon oxide layer is prepared by chemical vapor deposition.

5. The method for preparing a lithium niobate modulation device according to claim 1, wherein: The method also includes: filling the metal deposition tank with a metal protection medium, so that the metal protection medium completely fills the gaps in the metal deposition tank, and flattening the surface of the metal protection medium at the opening of the metal deposition tank and the surface of the waveguide substrate through chemical mechanical polishing.

6. The method for preparing a lithium niobate modulation device according to claim 1, wherein: The metal protection medium is a silicon oxide film.

7. The method for preparing a lithium niobate modulation device according to claim 2, wherein: The bottom of the metal deposition tank extends into the first silicon oxide layer, and the depth of the metal deposition tank is greater than 1 μm.

8. The method for preparing a lithium niobate modulation device according to claim 1, wherein: The thickness of the metal electrode does not exceed the depth of the metal deposition tank, and the top of the metal electrode is not higher than the top of the waveguide structure.

9. The method for preparing a lithium niobate modulation device according to claim 1, wherein: The lithium niobate substrate comprises a lithium niobate thin film layer, a third silicon oxide layer and a silicon substrate which are sequentially located on the waveguide substrate.

10. A lithium niobate modulation device prepared by the method according to any one of claims 1 to 9.

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