Lithium niobate modulation device and preparation method thereof

Abstract

The invention provides a lithium niobate modulation device and a preparation method thereof, and relates to the technical field of electro-optical modulators, and the preparation method of the lithium niobate modulation device comprises the steps: respectively preparing and forming metal deposition grooves in two sides of a waveguide structure of a waveguide substrate, and depositing metal electrodes in the metal deposition grooves; filling a metal protective medium in the metal deposition tank so as to completely cover the metal electrode through the metal protective medium; and bonding a lithium niobate substrate on the waveguide substrate after the metal electrode is formed to obtain the lithium niobate modulation device. According to the invention, the metal electrode deposition tank is prepared by etching the silicon oxide and grooving, and the metal electrode structure is prepared in the metal electrode deposition tank, so that the defect that the metal electrode is incompatible with a CMOS (Complementary Metal-Oxide-Semiconductor Transistor) process when the metal electrode is prepared after heterogeneous integration of the lithium niobate substrate and the waveguide substrate is optimized, and meanwhile, the low-temperature preparation of the waveguide structure is avoided; the optical loss of the waveguide structure is reduced, and the performance of the lithium niobate modulation device is improved.

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 is a platform that enables dense integration of photonic components and systems as well as electronic circuit integration. It is widely used in optical communications, gyroscopes and other fields due to its advantages such as low power consumption and low cost. Electro-optical modulation devices are tools that convert electrical signals into optical signals. They play a vital role in the above fields, transmitting electronic signals to optical carriers. With the rise of commercial integrated photonics, a variety of modulation platforms have been proven to be compatible with wafer-level manufacturing, among which lithium niobate materials have received widespread attention due to their excellent electro-optical modulation performance.

[0003] The commonly used technical solution is to use bonding and other processes to perform non-uniform heterogeneous integration of lithium niobate substrate and waveguide substrate. Among them, the metal electrode is mainly distributed in two positions, above or below the lithium niobate substrate: (1) The metal electrode is located above the lithium niobate substrate. This solution adopts 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 a waveguide substrate, and then heterogeneously integrates it with the lithium niobate substrate.

[0004] In the above solution (1), it is necessary to grow the metal electrode after bonding the lithium niobate substrate. Since the lithium niobate material will pollute the thin film growth chamber, it is difficult to be compatible with the CMOS process and cannot be applied on a large scale. In the above solution (2), since the metal electrode is prepared first and then the waveguide material is grown and patterned to form the waveguide structure, the metal electrode is difficult to withstand high temperature. The waveguide material needs to be prepared by plasma enhanced chemical vapor deposition (PECVD) technology. The low-temperature grown waveguide material (such as silicon nitride) has 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 method for preparing the same. The embodiment of the present application achieves compatibility with CMOS technology while avoiding low-temperature preparation of waveguide structure and reducing optical loss of the device by cutting grooves and growing metal electrodes in the grooves.

[0006] The embodiment of 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, respectively, and depositing metal electrodes in the metal deposition grooves;

[0008] Filling the metal deposition tank with a metal protection medium so that the metal electrode is completely covered by 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 an 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 also 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 an embodiment of the present application, the bottom of the metal deposition groove extends into the first silicon oxide layer, and the groove depth of the metal deposition groove is greater than 1 μm.

[0016] According to an 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 an 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 which are 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 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; finally, a lithium niobate substrate is bonded to the waveguide substrate after the metal electrodes are formed, to obtain the lithium niobate modulation device. The embodiment of the present invention prepares a metal deposition groove by etching silicon oxide to form grooves, and prepares a metal electrode structure in the metal deposition groove, thereby optimizing the defect of incompatibility with the CMOS process when preparing the metal electrode 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 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 drawings required for use in the embodiments will be briefly introduced below. 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 paying creative work.

[0021] Figure 1 It 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 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 in an embodiment of the present invention;

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

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

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

[0027] Among them, 10, 20 are silicon substrates, 11, 21 are silicon oxide layers prepared by thermal oxidation, 12 are silicon-rich silicon nitride waveguide layers, 13 are silicon nitride waveguide layers, 14 are silicon oxide layers prepared by chemical vapor deposition, 15 are metal deposition tanks, 16 are metal electrodes, 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 implementation methods of the present application through specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content 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 implementation methods, 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 ordinary technicians in the field without making creative work belong to the scope of protection of the present 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 that the metal electrode is completely covered by the metal protection medium;

[0033] 103. After forming the metal electrode, a lithium niobate substrate is bonded to the waveguide substrate 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, and prepares the metal electrode structure after the waveguide structure is prepared, thereby solving the defects of large optical loss and poor performance of the waveguide structure; it is compatible with the CMOS process and avoids the low-temperature preparation of the waveguide structure, thereby 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 waveguide structure, reduce device optical loss, and improve the performance of 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 specific implementation, the first silicon oxide layer is a silicon oxide layer prepared by thermal oxidation, and the second silicon oxide layer is a silicon oxide layer prepared by chemical vapor deposition. The two silicon oxide layers are non-same-layer thin film structures, and there is a silicon nitride waveguide structure in the middle: the first silicon oxide layer is prepared by thermal oxidation, which has the best density and film quality, and can be used as the lower silicon oxide layer to grow a silicon nitride thin film layer with good crystallization quality to optimize the optical performance; after the silicon nitride thin film layer is grown, it is impossible to continue to prepare silicon oxide by thermal oxidation, so the upper cladding silicon oxide is prepared by chemical vapor deposition to form the second silicon oxide layer, the film quality is slightly worse than the first silicon oxide layer, but it can be used as a cladding 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, that is, the waveguide structure includes a first waveguide structure layer and a second waveguide structure layer which are patterned on the first silicon oxide layer from bottom to top. 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 um. The specific dimensions of the three are determined according to current design conditions and process windows.

[0040] In order to meet the compatibility with CMOS process when preparing metal electrodes after heterogeneous integration of lithium niobate substrate and waveguide substrate, avoid preparing waveguide structure at low temperature, and reduce the optical loss of the device, in some embodiments of the present invention, the method further includes: filling the metal deposition tank with a metal protection medium, and making the metal protection medium fill all the gaps in the metal deposition tank, and flattening the surface of the metal protection medium and the waveguide substrate at the notch of the metal deposition tank by chemical mechanical polishing. The surface formed by the metal protection medium and the waveguide substrate is flattened for the subsequent bonding process of the lithium niobate substrate.

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

[0042] In the specific implementation, this embodiment uses plasma enhanced chemical vapor deposition (PECVD) to prepare silicon oxide film to fill the metal deposition groove, and forms a passivation layer on the surface of the metal electrode to protect the metal electrode: the silicon oxide film has a high resistivity, which can effectively prevent the current from flowing in an unwanted direction, thereby protecting the metal electrode; silicon oxide has good stability under most environmental conditions, is not 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, and will not cause obvious chemical reactions or interface defects. This compatibility enables silicon oxide to be closely attached to the surface of the metal electrode, providing a stable protective effect; in addition, the silicon oxide film prepared by PECVD technology has good etching groove filling properties, and will not introduce voids, gaps and other undesirable defects in the process of filling deep grooves. Therefore, silicon oxide film is often used as a protective layer and passivation layer of the device in the CMOS process.

[0043] Since the metal electrode needs to meet a certain thickness (~1μm) to ensure good electrical performance, the depth of the etched metal deposition groove is greater than 1μm, and the bottom of the metal deposition groove extends into the first silicon oxide layer. In some embodiments of the present invention, 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.

[0044] In some embodiments of the present invention, the metal deposition groove is located on both sides of the waveguide structure, and the bottom of the metal deposition groove 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 groove depth of the metal deposition groove, and the top of the metal electrode needs to be no higher than the top of the waveguide structure, and the gap is 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, that is, 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, optimize the optical performance and prepare 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 requirement of 100nm silicon oxide thickness on the silicon nitride waveguide layer, thereby affecting the optical performance, and 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 electrode damage.

[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 located on the waveguide substrate. The third silicon oxide layer is a silicon oxide layer prepared by thermal oxidation, and the third silicon oxide layer is prepared by thermal oxidation, which has the best density and film quality to optimize optical performance.

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

[0048] First, prepare a silicon nitride waveguide substrate such as Figure 2 As shown, the silicon nitride waveguide substrate includes: 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, which are formed in sequence.

[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 Again, a metal electrode 16 is deposited in the metal deposition tank 15, as shown in FIG. Figure 4 shown.

[0050] Next, a silicon oxide film is prepared to fill the metal deposition groove 15, thereby protecting 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 by 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] The embodiment of the present invention prepares a metal deposition groove by etching silicon oxide to form a groove, and prepares a metal electrode structure 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 is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope 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, respectively, and depositing metal electrodes in the metal deposition grooves; Filling the metal deposition tank with a metal protection medium so that the metal electrode is completely covered by 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, characterized in that: The method further comprises: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The metal protection medium is a silicon oxide film.

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

8. The method for preparing a lithium niobate modulation device according to claim 1, characterized in that: 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.

9. The method for preparing a lithium niobate modulation device according to claim 1, characterized in that: 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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