Preparation method of heterogeneous integrated electro-optical modulator

Abstract

The invention relates to the technical field of semiconductors, and discloses a preparation method of a heterogeneous integrated electro-optical modulator, which comprises the following steps: forming a processing intermediate comprising a bonding dielectric layer, a waveguide core at one side of the bonding dielectric layer and an electro-optical material layer at the other side of the bonding dielectric layer; forming a dielectric layer on the surface of the electro-optical material layer and the residual surface of the bonding dielectric layer; forming a first groove which penetrates through the dielectric layer and exposes edge areas corresponding to at least two edges of the electro-optical material layer and a part of the bonding dielectric layer; filling a sacrificial layer in the first groove; the polishing removal rate of the sacrificial layer is greater than that of the dielectric layer; and performing a chemical mechanical polishing process on the sacrificial layer, forming a second recess in the first groove, and forming a slope structure in an edge region corresponding to at least two edges of the electro-optical material layer. According to the invention, the technological process can be simplified, low-loss optical field transition between the waveguide core and the waveguide core-electro-optical material layer composite waveguide core is realized, and the insertion loss of the heterogeneous integrated electro-optical modulator is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a method for fabricating a heterogeneous integrated electro-optic modulation device. Background Technology

[0002] In related technologies, etching of electro-optic thin film materials such as lithium niobate is relatively difficult, making it challenging to form waveguide cores with low propagation loss. Furthermore, lithium niobate is incompatible with CMOS processes. Therefore, heterogeneous integration of lithium niobate and silicon nitride waveguide platforms is typically achieved by bonding a lithium niobate thin film onto a silicon nitride waveguide core to form a silicon nitride-lithium niobate composite waveguide core, thus creating electro-optic modulation devices based on the silicon nitride waveguide platform. One of the challenges in heterogeneous integration of lithium niobate and silicon nitride waveguide platforms is the low-loss transition of the optical field between the silicon nitride waveguide and the silicon nitride-lithium niobate composite waveguide. Existing solutions for achieving optical field transition between lithium niobate and silicon nitride waveguides all have certain drawbacks: Solution 1: Integrating a two-dimensional conical lithium niobate structure onto a silicon nitride platform using a micro-transfer process to achieve optical field transition. However, this solution requires etching a lithium niobate film to form a conical structure, and the two-dimensional conical structure and the silicon nitride waveguide core require high alignment precision, increasing the process difficulty. Solution 2: Performing multiple dry etching processes on lithium niobate to form multiple steps along both sides of the silicon nitride waveguide core to achieve optical field transition. Since dry etching of lithium niobate is relatively difficult, the process is complex and has potential contamination issues, which can lead to incompatibility with CMOS process equipment. Solution 3: Using a silicon-rich silicon nitride waveguide core with a higher refractive index than lithium niobate for interlayer coupling to achieve optical field transition. However, this solution has high absorption loss in silicon-rich silicon nitride and introduces more film layers, complicating the device and process.

[0003] Therefore, a solution is needed that avoids etching the electro-optic material layer to form a transition structure, thereby achieving a low-loss transition between the silicon nitride waveguide and the silicon nitride-lithium niobate composite waveguide, and thus reducing the insertion loss of heterogeneous integrated electro-optic phase modulation devices. Summary of the Invention

[0004] In view of this, the present invention provides a method for fabricating a heterogeneous integrated electro-optic modulation device to solve the problems in related technologies, such as the high difficulty of micro-transfer printing of two-dimensional conical lithium niobate structure, the need for multiple dry etching of lithium niobate, and the high absorption loss of silicon-rich silicon nitride, which leads to high optical field transition loss between silicon nitride waveguide and silicon nitride-lithium niobate composite waveguide, as well as the complexity of device structure and process.

[0005] In a first aspect, the present invention provides a method for fabricating a heterogeneous integrated electro-optic modulation device, the method comprising:

[0006] A processing intermediate comprising a waveguide core and an electro-optic material layer is formed. The processing intermediate includes a bonding dielectric layer, a waveguide core on one side of the bonding dielectric layer, and an electro-optic material layer on the other side of the bonding dielectric layer. The projection of the electro-optic material layer on the bonding dielectric layer partially overlaps with the projection of the waveguide core on the bonding dielectric layer. The bonding dielectric layer also covers the side of the waveguide core.

[0007] A dielectric layer is formed on the side surface of the electro-optic material layer that is opposite to the bonding dielectric layer. The dielectric layer also covers the remaining surface of the bonding dielectric layer that is not covered by the electro-optic material layer and the side surface of the electro-optic material layer.

[0008] A first groove is formed on the side of the dielectric layer facing away from the electro-optic material layer. The first groove penetrates the dielectric layer and exposes the edge regions corresponding to at least two sides of the electro-optic material layer and part of the bonding dielectric layer. The region of the dielectric layer outside the first groove is the second region.

[0009] A sacrificial layer is filled in the first groove; the polishing removal rate of the sacrificial layer is greater than that of the dielectric layer.

[0010] A chemical mechanical polishing process is performed on the sacrificial layer to remove part of the dielectric layer in the second region, as well as part of the sacrificial layer and part of the electro-optic material layer in the first groove. A second depression is formed in the sacrificial layer and electro-optic material layer in the first groove. The second depression forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer. The depth of the second depression gradually decreases from the center to the edge of the first groove. The second depression exposes the bonding dielectric layer. The projection of the slope structure of the electro-optic material layer on the bonding dielectric layer intersects with the projection of the waveguide core on the bonding dielectric layer.

[0011] The method for fabricating a heterogeneous integrated electro-optic modulation device provided by the present invention first forms a dielectric layer and a first groove on a processing intermediate comprising a waveguide core and an electro-optic material layer. The first groove exposes the edge regions corresponding to at least two sides of the electro-optic material layer and a portion of the bonded dielectric layer. Second, a sacrificial layer is filled in the first groove as a polishing mask for the electro-optic material layer. The polishing removal rate of the sacrificial layer is greater than that of the dielectric layer. Finally, when two materials with different polishing removal rates are simultaneously subjected to a chemical mechanical polishing process, a phenomenon of gradually deepening depressions from the edge to the center will be formed on the material with the faster polishing removal rate between the materials with slower polishing removal rates. A second depression is formed in the sacrificial layer and the electro-optic material layer in the first groove. The second depression forms a slope structure in the edge regions corresponding to at least two sides of the electro-optic material layer. On the one hand, by using chemical mechanical polishing (CMP) to create a second depression based on the polishing characteristics of materials with different polishing removal rates, an electro-optic material layer with a slope structure on at least two sides is formed. This slope structure fabrication process is simple, efficient, and has high electro-optic material utilization. Furthermore, it eliminates the need for etching the electro-optic material layer, reducing process difficulty and simplifying the fabrication process. On the other hand, the slope structure fabrication method in this solution has lower alignment accuracy requirements and avoids absorption losses due to additional materials. The resulting slope structure has low surface roughness and a smooth surface. The projection of the slope structure onto the bonding dielectric layer intersects with the projection of the waveguide core onto the bonding dielectric layer, resulting in lower transition loss between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core. Therefore, the fabrication method for the electro-optic modulation device provided by this invention simplifies the process flow, reduces process difficulty, and improves process efficiency, effectively reducing the optical field transition loss of the electro-optic modulation device. This enables low-loss optical field transition between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of heterogeneous integrated electro-optic modulation devices.

[0012] In one alternative implementation, during the step of filling the sacrificial layer in the first groove, the sacrificial layer also covers the surface of the dielectric layer in the second region.

[0013] The chemical mechanical polishing process for the sacrificial layer also includes removing the sacrificial layer and part of the dielectric layer in the second region.

[0014] In one optional embodiment, the chemical mechanical polishing process sequentially includes a first polishing stage and a second polishing stage;

[0015] The first polishing stage includes: removing the sacrificial layer and part of the dielectric layer in the second region, as well as part of the sacrificial layer in the first groove, forming a sacrificial layer depression on the surface of the sacrificial layer in the first groove, the thickness of the sacrificial layer gradually decreasing from the edge of the first groove to the center until the depth of the sacrificial layer depression no longer increases, thus forming the first depression; the first polishing removal rate of the sacrificial layer is greater than the polishing removal rate of the dielectric layer.

[0016] The second polishing stage includes: removing part of the dielectric layer in the second region, as well as part of the sacrificial layer and part of the electro-optic material layer in the first groove; the first depression is transferred to the electro-optic material layer to form a second depression; the second depression exposes the bonding dielectric layer; the second depression forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer; the thickness of the slope structure gradually decreases along the direction away from the center of the electro-optic material layer; the second polishing removal rate of the sacrificial layer is equal to the polishing removal rate of the dielectric layer.

[0017] The method for fabricating a heterogeneous integrated electro-optic modulation device provided by this invention involves the following steps: In the first polishing stage, by controlling the first polishing removal rate of the sacrificial layer in the first groove to be greater than the polishing removal rate of the dielectric layer in the second region, a first depression is formed in the sacrificial layer of the first groove. In the second polishing stage, since the first depression has been saturated, the second polishing removal rate of the sacrificial layer is equal to the polishing removal rate of the dielectric layer, and the first depression is transferred to the electro-optic material layer to form a second depression. The second depression forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer. The fabrication process of the slope structure is simple. It only requires controlling the polishing removal rates of the sacrificial layer and the dielectric layer in the two polishing stages to form an electro-optic material layer with a slope structure on at least two sides through chemical mechanical polishing. This simplifies the process flow, reduces the process difficulty, and improves the process efficiency, thereby effectively reducing the optical field transition loss of the electro-optic modulation device.

[0018] In one alternative embodiment, during the first polishing stage, the first depression is a saturated depression; the depth of the saturated depression is positively correlated with the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer.

[0019] In the second polishing stage, the polishing removal rate of the electro-optic material layer is greater than or equal to the polishing removal rate of the dielectric layer; the polishing removal rate of the bonded dielectric layer is not greater than the polishing removal rate of the dielectric layer; and the depth of the second depression is greater than or equal to the depth of the first depression.

[0020] The method for fabricating a heterogeneous integrated electro-optic modulator provided by this invention includes the following steps: In the first polishing stage, the first depression is a saturated depression. The depth of the saturated depression is positively correlated with the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer. Therefore, the depth of the first depression and the subsequent second depression can be controlled by controlling the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer, thereby controlling the slope of the slope structure. In the second polishing stage, the polishing removal rate of the electro-optic material layer is greater than or equal to the polishing removal rate of the dielectric layer. This allows the first depression to be completely transferred to the electro-optic material layer, making the depth of the second depression greater than or equal to the depth of the first depression. This allows for more precise control of the slope of the slope structure, further reducing the optical field transition loss between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of the heterogeneous integrated electro-optic modulator, and thus improving the performance of the heterogeneous integrated electro-optic modulator.

[0021] In one optional embodiment, the dielectric layer is made of silicon dioxide, the sacrificial layer is made of copper, and the electro-optic material layer is made of lithium niobate.

[0022] In one alternative embodiment, during the step of forming the first groove, at least two sides of the electro-optic material layer exposed by the first groove are located on the center line of the first groove;

[0023] In the chemical mechanical polishing process of the sacrificial layer, the thickness of the resulting slope structure gradually decreases to 0 along the direction away from the center of the electro-optic material layer.

[0024] The method for fabricating a heterogeneous integrated electro-optic modulation device provided by the present invention controls at least two sides of the electro-optic material layer exposed in the first groove to be located on the center line of the first groove. This allows the bonding dielectric layer to be prevented from being polished before the edge thickness of the electro-optic material layer is reduced to 0. This reduces the polishing time of the bonding dielectric layer, reduces the loss of the bonding dielectric layer, and protects the waveguide core from polishing damage. At the same time, it can shorten the polishing time and improve the process efficiency.

[0025] In one alternative embodiment, the step of forming a processing intermediate comprising a waveguide core and an electro-optic material layer includes:

[0026] An electro-optic material unit and a waveguide core wafer are provided; the electro-optic material unit includes a first substrate, a buried layer and an electro-optic material layer stacked together; the waveguide core wafer includes a second substrate, a lower cladding layer, a waveguide core and a bonding dielectric layer stacked together, the bonding dielectric layer covering the side surface of the waveguide core facing away from the second substrate and the side surface of the waveguide core;

[0027] At least one electro-optic material unit is bonded to the side surface of the bonding dielectric layer facing away from the waveguide core, and the first substrate is removed; the projection of the electro-optic material unit on the bonding dielectric layer partially overlaps with the projection of the waveguide core on the bonding dielectric layer.

[0028] Following the chemical mechanical polishing process on the sacrificial layer, the process also includes:

[0029] Remove the remaining sacrificial layer and form a second groove at the location of the first groove. The second groove penetrates the dielectric layer and exposes the slope structure corresponding to at least two sides of the electro-optic material layer and part of the bonding dielectric layer.

[0030] Multiple electrodes are formed on the side of the dielectric layer facing away from the electro-optic material layer, with the electrodes located at corresponding positions on both sides of the waveguide core.

[0031] In one alternative embodiment, the projection of the electro-optic material layer onto the bonding dielectric layer is rectangular;

[0032] The first groove penetrates the dielectric layer and the buried layer, and exposes at least one set of opposing edges of the electro-optic material layer; the projection of the waveguide core on the bonding dielectric layer intersects with the projection of the first groove on the bonding dielectric layer; the projection of the first groove on the bonding dielectric layer includes at least two parallel rectangles.

[0033] The second depression forms a slope structure in the edge region corresponding to at least one set of opposite sides of the electro-optic material layer;

[0034] The electrodes are located at least on the surface of the dielectric layer corresponding to the electro-optic material layers on both sides of the waveguide core.

[0035] The method for fabricating a heterogeneous integrated electro-optic modulator provided by the present invention controls at least a set of opposite edges of the electro-optic material layer to be exposed by the first groove; the projection of the waveguide core on the bonding dielectric layer intersects with the projection of the first groove on the bonding dielectric layer, so that the projection of the formed slope structure on the bonding dielectric layer intersects with the projection of the waveguide core on the bonding dielectric layer, thereby reducing the optical field transition loss between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of the heterogeneous integrated electro-optic modulator, and thus improving the performance of the heterogeneous integrated electro-optic modulator.

[0036] In one alternative embodiment, the first groove exposes the edge regions corresponding to the four sides of the electro-optic material layer; the projection of the first groove onto the bonding dielectric layer is a closed annular rectangle;

[0037] The second depression forms a slope structure in the edge region corresponding to the four sides of the electro-optic material layer;

[0038] The electrodes are located on both sides of the waveguide core, at least partially on the surface of the dielectric layer corresponding to the electro-optic material layer.

[0039] In one alternative implementation, after the step of removing the remaining sacrificial layer and before the step of forming multiple electrodes on the side of the dielectric layer opposite to the buried layer, the method further includes:

[0040] An upper cladding layer is formed on the surface of the dielectric layer facing away from the buried layer, and the upper cladding layer also fills a second groove;

[0041] In the step of forming multiple electrodes on the side of the dielectric layer facing away from the buried layer, the electrodes are located on the upper cladding surface corresponding to the electro-optic material layers on both sides of the waveguide core. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of the present invention, the drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a schematic flowchart of a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram illustrating the specific process of fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention.

[0045] Figure 3 This is a schematic diagram of the structure of an electro-optic material unit in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention.

[0046] Figure 4 This is a schematic diagram of the waveguide core wafer structure in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention.

[0047] Figure 5A and Figure 5B This is a schematic diagram of the bonding of electro-optic material units to waveguide core wafers in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 5B for Figure 5A Cross-sectional view of plane AA.

[0048] Figure 6A and Figure 6B This is a schematic diagram of the structure of a processing intermediate formed in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 6B for Figure 6A Cross-sectional view of plane AA.

[0049] Figure 7 In a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention, in Figure 6B A schematic diagram of the structure in which a dielectric layer is formed on the basis.

[0050] Figure 8A , Figure 8B and Figure 8C This is a schematic diagram of the structure forming the first groove in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 8C for Figure 8A or Figure 8B Cross-sectional view of plane AA.

[0051] Figure 9 In a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention, in Figure 8B A schematic diagram of the structure that forms the sacrificial layer on the basis.

[0052] Figure 10A , Figure 10B and Figure 10C This is a schematic diagram of the structure forming the first recess in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 10C for Figure 10A or Figure 10B Cross-sectional view of plane AA.

[0053] Figure 11A , Figure 11B and Figure 11C This is a schematic diagram of the structure forming the second recess in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 11C for Figure 11A or Figure 11B Cross-sectional view of plane AA.

[0054] Figure 12A , Figure 12B and Figure 12C This is a schematic diagram of the structure after removing the remaining sacrificial layer in a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 12C for Figure 12A or Figure 12B Cross-sectional view of plane AA.

[0055] Figure 13A and Figure 13B This is a schematic diagram of the electrode structure in Example 1 of a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 13B for Figure 13A Cross-sectional view of the BB side.

[0056] Figure 14A and Figure 14B This is a schematic diagram of the electrode structure in Example 2 of a method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 14B for Figure 14A Cross-sectional view of the BB side.

[0057] Figure 15A , Figure 15B and Figure 15C This is a schematic diagram of the structure forming the upper cladding in Example 1 of another method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 15B for Figure 15A Cross-sectional view of plane AA, Figure 15C for Figure 15A Cross-sectional view of the BB side.

[0058] Figure 16A and Figure 16B This is a schematic diagram of the electrode structure in Example 1 of another method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 16B for Figure 16A Cross-sectional view of the BB side.

[0059] Figure 17A , Figure 17B and Figure 17C This is a schematic diagram of the upper cladding structure in Example 2 of another method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 17B for Figure 17A Cross-sectional view of plane AA, Figure 17C for Figure 17A Cross-sectional view of the BB side.

[0060] Figure 18A and Figure 18B This is a schematic diagram of the electrode structure in Example 2 of another method for fabricating a heterogeneous integrated electro-optic modulation device according to an embodiment of the present invention. Figure 18B for Figure 18A Cross-sectional view of the BB side.

[0061] Figure label:

[0062] 10. First substrate; 11. Buried layer; 12. Electro-optic material layer; 20. Second substrate; 21. Lower cladding layer; 22. Waveguide core; 23. Bonding dielectric layer; 30. Dielectric layer; 40. Sacrificial layer; 50. Upper cladding layer; 60. Electrode; 91. First recess; 92. Second recess. Detailed Implementation

[0063] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention, not the entire structure.

[0064] In the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These drawings are not to scale, and some details are enlarged for clarity, and some details may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0065] like Figure 1 As shown, this embodiment provides a method for fabricating a heterogeneous integrated electro-optic modulation device, which includes, but is not limited to, steps S101 to S105.

[0066] Step S101: A processing intermediate comprising a waveguide core 22 and an electro-optic material layer 12 is formed. The processing intermediate includes a bonding dielectric layer 23, a waveguide core 22 on one side of the bonding dielectric layer 23, and an electro-optic material layer 12 on the other side of the bonding dielectric layer 23. The projection of the electro-optic material layer 12 onto the bonding dielectric layer 23 partially overlaps with the projection of the waveguide core 22 onto the bonding dielectric layer 23. The bonding dielectric layer 23 also covers the side surface of the waveguide core 22, such as... Figure 6A and Figure 6B As shown.

[0067] In step S102, a dielectric layer 30 is formed on the surface of the electro-optic material layer 12 facing away from the bonding dielectric layer 23. The dielectric layer 30 also covers the remaining surface of the bonding dielectric layer 23 not covered by the electro-optic material layer 12 and the side surface of the electro-optic material layer 12, such as... Figure 7 As shown.

[0068] In step S103, a first groove is formed on the side of the dielectric layer 30 facing away from the electro-optic material layer 12. The first groove penetrates the dielectric layer 30 and exposes the edge regions corresponding to at least two sides of the electro-optic material layer 12 and part of the bonding dielectric layer 23. The region of the dielectric layer 30 outside the first groove is the second region, such as... Figure 8A , Figure 8B and Figure 8C As shown.

[0069] Step S104: Fill the first groove with a sacrificial layer 40; the polishing removal rate of the sacrificial layer 40 is greater than the polishing removal rate of the dielectric layer 30, such as... Figure 9 As shown.

[0070] Step S105: Perform chemical mechanical polishing on the sacrificial layer 40 to remove part of the dielectric layer 30 in the second region, as well as part of the sacrificial layer 40 and part of the electro-optic material layer 12 in the first groove. A second recess 92 is formed in the sacrificial layer 40 and electro-optic material layer 12 in the first groove. The second recess 92 forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer 12. The depth of the second recess 92 gradually decreases from the center to the edge of the first groove. The second recess 92 exposes the bonding dielectric layer 23. The projection of the slope structure of the electro-optic material layer 12 onto the bonding dielectric layer 23 intersects with the projection of the waveguide core 22 onto the bonding dielectric layer 23. Figure 11A , Figure 11B and Figure 11C As shown.

[0071] During chemical mechanical polishing (CMP), when a polishing pad simultaneously contacts two materials, as CMP progresses, a depression gradually deepens from the edge to the center on the material with the faster removal rate between the materials with slower removal rates. This invention utilizes this characteristic of the CMP process to create depressions in the sacrificial layer with the faster removal rate between the dielectric layers with slower removal rates. Using this depressed sacrificial layer as a CMP mask for the electro-optic material layer, a slope structure with gradually decreasing thickness is formed in the edge regions corresponding to at least two sides of the electro-optic material layer 12.

[0072] In practice, a dielectric layer 30 with a slow removal rate is used to cover the center and peripheral areas of the electro-optic material layer 12, while a sacrificial layer 40 with a fast removal rate is used to cover the edge areas corresponding to at least two sides of the electro-optic material layer 12 and their vicinity. Then, centrifugal particle (CMP) is performed, forming a depression on the sacrificial layer 40 with the fast removal rate. As CMP progresses, the material thickness of both the dielectric layer 30 and the sacrificial layer 40 decreases, gradually exposing and polishing the electro-optic material layer 12. The thickness gradient on the sacrificial layer 40 (thicker material at the edge of the depression, thinner material in the middle) is transferred to the electro-optic material layer 12, forming a second depression 92. This creates a slope structure with gradually decreasing thickness in the edge areas corresponding to at least two sides of the electro-optic material layer 12. The slope structure facilitates a low-loss optical field transition between the silicon nitride waveguide and the silicon nitride-lithium niobate composite waveguide.

[0073] The method for fabricating a heterogeneous integrated electro-optic modulation device provided in this embodiment first forms a dielectric layer and a first groove on a processing intermediate containing a waveguide core and an electro-optic material layer. The first groove exposes the edge regions corresponding to at least two sides of the electro-optic material layer and part of the bonding layer. Next, a sacrificial layer is filled in the first groove as a polishing mask for the electro-optic material layer. The polishing removal rate of the sacrificial layer is greater than that of the dielectric layer. Finally, when two materials with different polishing removal rates are simultaneously subjected to chemical mechanical polishing, a phenomenon of gradually deepening depressions from the edge to the center will be formed on the material with the faster polishing removal rate between the materials with slower polishing removal rates. A second depression is formed in the sacrificial layer and the electro-optic material layer in the first groove. The second depression forms a slope structure in the edge regions corresponding to at least two sides of the electro-optic material layer. On the one hand, by using chemical mechanical polishing (CMP) to create a second depression based on the polishing characteristics of materials with different polishing removal rates, an electro-optic material layer with a slope structure on at least two sides is formed. This slope structure fabrication process is simple, efficient, and has high electro-optic material utilization. Furthermore, it eliminates the need for etching the electro-optic material layer, reducing process difficulty and simplifying the fabrication process. On the other hand, the slope structure fabrication method in this solution has lower alignment accuracy requirements and avoids absorption losses due to additional materials. The resulting slope structure has low surface roughness and a smooth surface. The projection of the slope structure onto the bonding dielectric layer intersects with the projection of the waveguide core onto the bonding dielectric layer, resulting in lower transition losses between the waveguide core of the electro-optic modulation device and the waveguide core-electro-optic material layer composite waveguide core. Therefore, the fabrication method for the electro-optic modulation device provided by this invention simplifies the process flow, reduces process difficulty, and improves process efficiency, effectively reducing the optical field transition loss of the electro-optic modulation device. This enables low-loss optical field transition between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of heterogeneous integrated electro-optic modulation devices.

[0074] In some alternative embodiments, during the step of filling the first groove with the sacrificial layer 40, the sacrificial layer 40 also covers the surface of the dielectric layer 30 in the second region;

[0075] The chemical mechanical polishing process for the sacrificial layer 40 also includes removing the sacrificial layer 40 and part of the dielectric layer 30 in the second region.

[0076] In some optional embodiments, the chemical mechanical polishing process includes a first polishing stage and a second polishing stage in sequence;

[0077] The first polishing stage includes: removing the sacrificial layer 40 and part of the dielectric layer 30 in the second region, as well as part of the sacrificial layer 40 in the first groove, forming a sacrificial layer depression on the surface of the sacrificial layer 40 in the first groove, the thickness of the sacrificial layer 40 gradually decreasing from the edge of the first groove to the center until the depth of the sacrificial layer depression no longer increases, forming the first depression 91; the first polishing removal rate of the sacrificial layer 40 is greater than the polishing removal rate of the dielectric layer 30.

[0078] The second polishing stage includes: removing a portion of the dielectric layer 30 in the second region, as well as a portion of the sacrificial layer 40 and a portion of the electro-optic material layer 12 within the first groove; the first depression 91 is transferred to the electro-optic material layer 12 to form a second depression 92; the second depression 92 exposes the bonding dielectric layer 23; the second depression 92 forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer 12; the thickness of the slope structure gradually decreases along the direction away from the center of the electro-optic material layer 12; the second polishing removal rate of the sacrificial layer 40 is equal to the polishing removal rate of the dielectric layer 30.

[0079] It should be noted that the second polishing removal rate of the sacrificial layer 40 in the second polishing stage is equal to the polishing removal rate of the dielectric layer 30. Here, the second polishing removal rate refers to the actual removal rate of the sacrificial layer 40. Under the condition of fixed CMP process parameters, the polishing removal rate of the sacrificial layer 40 is fixed. Since the depth of the sacrificial layer recess no longer increases after the formation of the first recess 91 in the first polishing stage, the depth of the first recess 91 is maintained in the second polishing stage and no longer increases. That is, the actual removal rates of the dielectric layer 30 and the sacrificial layer 40 in the first recess in the second region are the same. The surface heights of the dielectric layer 30 and the sacrificial layer 40 decrease synchronously, thereby gradually exposing the edge of the electro-optic material layer 12 and polishing it with the sacrificial layer recess and / or the bonding dielectric layer 23 (when it is exposed) as a mask. The thickness gradient of the sacrificial layer 40 is gradually transferred to the exposed electro-optic material layer 12, forming a slope structure with gradually decreasing thickness at the edge of the electro-optic material layer 12.

[0080] The method for fabricating a heterogeneous integrated electro-optic modulation device provided in this embodiment involves the following steps: In the first polishing stage, by controlling the first polishing removal rate of the sacrificial layer in the first groove to be greater than the polishing removal rate of the dielectric layer in the second region, a first depression is formed in the sacrificial layer of the first groove. In the second polishing stage, since the first depression has been saturated, the second polishing removal rate of the sacrificial layer is equal to the polishing removal rate of the dielectric layer. The first depression is transferred to the electro-optic material layer to form a second depression. The second depression forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer. The fabrication process of the slope structure is simple. It only requires controlling the polishing removal rates of the sacrificial layer and the dielectric layer in the two polishing stages to form an electro-optic material layer with a slope structure on at least two sides through chemical mechanical polishing. This simplifies the process flow, reduces the process difficulty, and improves the process efficiency, thereby effectively reducing the optical field transition loss of the electro-optic modulation device.

[0081] In some alternative embodiments, the ratio of the horizontal length of the slope structure formed by the edge of the electro-optic material layer 12 to the thickness of the electro-optic material layer 12 can be from 10:1 to 500:1. The ratio of the first polishing removal rate of the sacrificial layer 40 to the polishing removal rate of the dielectric layer 30 depends primarily on the polishing fluid composition and polishing process parameters (such as pressure, temperature, etc.). Considering a single variable, an increase in the ratio of the first polishing removal rate of the sacrificial layer 40 to the polishing removal rate of the dielectric layer 30, a decrease in the stiffness of the polishing pad, and an increase in the width of the first groove will lead to a deeper sacrificial layer depression. The smaller the width of the sacrificial layer depression (i.e., the width of the first groove) and the greater the depth, the steeper the surface slope of the sacrificial layer depression. For the already formed sacrificial layer depression, the surface slope is larger on the side closer to the dielectric layer 30 and smaller on the side closer to the center of the first groove. The edge of the electro-optic material layer 12 is formed into a slope structure using a sacrificial layer recess as a polished mask. Therefore, the slope gradient of the slope structure is related to the shape (depth and width) of the sacrificial layer recess and the position of the end of the electro-optic material layer 12 in the first groove: a narrow and deep sacrificial layer recess or an end of the electro-optic material layer 12 far from the center of the first groove will result in an increased slope gradient of the slope structure. In addition, the thickness of the sacrificial layer recess and the resulting slope structure of the electro-optic material layer 12 exhibits a non-linear variation.

[0082] In some alternative embodiments, during the first polishing stage, the first depression 91 is a saturated depression; the depth of the saturated depression is positively correlated with the ratio of the first polishing removal rate of the sacrificial layer 40 to the polishing removal rate of the dielectric layer 30.

[0083] In the second polishing stage, the polishing removal rate of the electro-optic material layer 12 is greater than or equal to the polishing removal rate of the dielectric layer 30; the polishing removal rate of the bonding dielectric layer 23 is not greater than the polishing removal rate of the dielectric layer 30; and the depth of the second recess 92 is greater than or equal to the depth of the first recess 91.

[0084] In specific implementation, during the first polishing stage, the saturation depth of the sacrificial layer depression (i.e., the first depression 91) is related to the sacrificial layer-dielectric layer removal rate ratio, CMP process conditions (such as temperature, pressure, rotation speed, etc.), the stiffness of the polishing pad, and the groove width. As the groove width increases, the sacrificial layer-dielectric layer polishing removal rate ratio increases, the polishing pad becomes softer, the CMP process pressure increases, and the temperature rises, the saturation depth of the sacrificial layer depression (i.e., the first depression 91) tends to increase. During the second polishing stage, the second polishing removal rate of the sacrificial layer 40 is equal to the polishing removal rate of the dielectric layer 30, and the polishing removal rate of the electro-optic material layer 12 is equal to the polishing removal rate of the dielectric layer 30. That is, the surfaces of the dielectric layer, sacrificial layer, and electro-optic material layer descend synchronously, propagating the first depression downwards until the bonding dielectric layer is exposed, forming the second depression. The polishing removal rate of the bonding dielectric layer 23 is not greater than the polishing removal rate of the dielectric layer 30, therefore it will not cause significant damage to the bonding dielectric layer, thus protecting the waveguide core 22.

[0085] The fabrication method of the heterogeneous integrated electro-optic modulator provided in this embodiment includes the following steps: In the first polishing stage, the first depression is a saturated depression. The depth of the saturated depression is positively correlated with the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer. Therefore, the depth of the first depression and the subsequent second depression can be controlled by controlling the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer, thereby controlling the slope of the slope structure. In the second polishing stage, the polishing removal rate of the electro-optic material layer is equal to the polishing removal rate of the dielectric layer. This allows the first depression to be completely transferred to the electro-optic material layer, making the depth of the second depression greater than or equal to the depth of the first depression. This allows for more precise control of the slope of the slope structure, further reducing the optical field transition loss between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of the heterogeneous integrated electro-optic modulator, and thus improving the performance of the heterogeneous integrated electro-optic modulator.

[0086] In some optional embodiments, during the second polishing stage, the polishing removal rate of the electro-optic material layer is similar to that of the dielectric layer, i.e., the first deviation between the polishing removal rate of the electro-optic material layer and the dielectric layer is less than 5%; the depth of the second depression is similar to the depth of the first depression, i.e., the second deviation between the depth of the second depression and the depth of the first depression is less than 5%. Here, the second deviation refers to the ratio of the difference in polishing removal rates between the electro-optic material layer and the dielectric layer to the polishing removal rate of the dielectric layer; the second deviation also refers to the ratio of the difference in depth between the second depression and the first depression to the depth of the first depression. At this point, the first depression is substantially homomorphically transferred downwards to form the second depression.

[0087] In some alternative embodiments, during the second polishing stage, the polishing removal rate of the electro-optic material layer is equal to that of the dielectric layer; the depth of the second depression is equal to the depth of the first depression. At this point, the first depression is completely isomorphically transferred downwards to form the second depression.

[0088] In some alternative embodiments, the dielectric layer 30 is made of silicon dioxide, the sacrificial layer 40 is made of copper, and the electro-optic material layer 12 is made of lithium niobate.

[0089] In the chemical mechanical polishing process, the polishing slurry includes copper polishing slurry and hydrogen peroxide oxidant. The mass fraction of hydrogen peroxide in the polishing slurry can be 0.1% to 10%, the polishing pressure is 3psi to 5psi, the rotation speed of the polishing head is 30r / min to 120r / min, the rotation speed of the polishing pad is 30r / min to 120r / min, and the flow rate of the polishing slurry is 50ml / min to 300ml / min.

[0090] In some alternative embodiments, the width of the edge region corresponding to each side of the electro-optic material layer 12 exposed by the first groove is less than or equal to half the width of the first groove; the thickness of the formed slope structure gradually decreases along the direction away from the center of the electro-optic material layer 12; and the polishing removal rate of the bonding dielectric layer 23 is not greater than the polishing removal rate of the dielectric layer 30.

[0091] Preferably, the thickness of the formed slope structure gradually decreases to 0 along the direction away from the center of the electro-optic material layer 12. A simple and effective method to achieve the reduction of the edge thickness of the electro-optic material layer 12 to 0 is to make the edge of the bonding dielectric layer 23 as close as possible to the center of the first groove, because the sacrificial layer is deepest at the center, and the bonding dielectric layer 23 or the electro-optic material layer 12 at this location is exposed and polished earlier. The closer the edge of the electro-optic material layer 12 is to the center of the first groove, the earlier the electro-optic material layer 12 is exposed and polished (while the bonding dielectric layer 23 has not yet been exposed), and the shorter the polishing time and the less wear of the bonding dielectric layer 23 before the edge thickness of the electro-optic material layer 12 decreases to 0 (even if the electro-optic material layer 12 is relatively thick). Conversely, the further the edge of the electro-optic material layer 12 is from the center of the first groove, the later the edge of the electro-optic material layer 12 is exposed and polished (the bonding dielectric layer 23 may have already been exposed and polished before the edge of the electro-optic material layer 12 is exposed). Therefore, the bonding dielectric layer 23 takes longer to polish and suffers more wear before the thickness of the edge of the electro-optic material layer 12 is reduced to 0 (even if the electro-optic material layer 12 is relatively thin). In addition, from the perspective of the geometric continuity of the material surface, the thickness of the edge of the electro-optic material layer 12 can only be reduced to 0 when the sacrificial layer 40 adjacent to the edge of the electro-optic material layer 12 is completely consumed. For this purpose, the bonding dielectric layer 23 needs to be exposed and subjected to a certain degree of polishing. Therefore, the bonding dielectric layer 23 should have a low removal rate to ensure that the bonding dielectric layer 23 is not completely consumed, thereby protecting the waveguide core 22 from polishing damage.

[0092] In some alternative embodiments, during the step of forming the first groove, at least two sides of the electro-optic material layer 12 exposed by the first groove are located on the center line of the first groove;

[0093] In the chemical mechanical polishing process of the sacrificial layer 40, the thickness of the resulting slope structure gradually decreases to 0 along the direction away from the center of the electro-optic material layer 12.

[0094] The method for fabricating a heterogeneous integrated electro-optic modulation device provided in this embodiment controls at least two edges of the electro-optic material layer 12 exposed in the first groove to be located on the center line of the first groove. This allows the bonding dielectric layer 23 to be prevented from being polished before the edge thickness of the electro-optic material layer 12 is reduced to 0. This reduces the polishing time of the bonding dielectric layer 23, lowers the loss of the bonding dielectric layer 23, and protects the waveguide core 22 from polishing damage. At the same time, it can shorten the polishing time and improve process efficiency.

[0095] In some alternative embodiments, the step of forming a processing intermediate comprising waveguide core 22 and electro-optic material layer 12 includes:

[0096] An electro-optic material unit and a waveguide core 22 wafer are provided; the electro-optic material unit includes a first substrate 10, a buried layer 11 and an electro-optic material layer 12 stacked together; the waveguide core 22 wafer includes a second substrate 20, a lower cladding layer 21, a waveguide core 22 and a bonding dielectric layer 23 stacked together, the bonding dielectric layer 23 covering the side surface of the waveguide core 22 facing away from the second substrate 20 and the side surface of the waveguide core 22;

[0097] At least one electro-optic material unit is bonded to the side surface of the bonding dielectric layer 23 facing away from the waveguide core 22, and the first substrate 10 is removed to form a processing intermediate containing the waveguide core 22 and the electro-optic material layer 12; the projection of the electro-optic material unit on the bonding dielectric layer 23 partially overlaps with the projection of the waveguide core 22 on the bonding dielectric layer 23.

[0098] Following the chemical mechanical polishing process on the sacrificial layer 40, the process also includes:

[0099] Remove the remaining sacrificial layer 40 and form a second groove at the location of the first groove. The second groove penetrates the dielectric layer 30 and exposes the slope structure corresponding to at least two sides of the electro-optic material layer 12 and part of the bonding dielectric layer 23.

[0100] Multiple electrodes 60 are formed on the side of the dielectric layer 30 facing away from the electro-optic material layer 12, and the electrodes 60 are located at corresponding positions on both sides of the waveguide core 22.

[0101] In some alternative embodiments, the projection of the electro-optic material layer 12 onto the bonding dielectric layer 23 is rectangular;

[0102] The first groove penetrates the dielectric layer 30 and the buried layer 11, and exposes at least one set of opposing edges of the electro-optic material layer 12; the projection of the waveguide core 22 on the bonding dielectric layer 23 intersects with the projection of the first groove on the bonding dielectric layer 23; the projection of the first groove on the bonding dielectric layer 23 includes at least two parallel rectangles.

[0103] The second depression 92 forms a slope structure in the edge region corresponding to at least one set of opposite sides of the electro-optic material layer 12;

[0104] Electrode 60 is located at least on the surface of dielectric layer 30 corresponding to electro-optic material layer 12 on both sides of waveguide core 22.

[0105] The method for fabricating a heterogeneous integrated electro-optic modulator provided in this embodiment controls the first groove to expose at least a set of opposite edges of the electro-optic material layer. The projection of the waveguide core on the bonding dielectric layer intersects with the projection of the first groove on the bonding dielectric layer. This allows the projection of the formed slope structure on the bonding dielectric layer to intersect with the projection of the waveguide core on the bonding dielectric layer, thereby reducing the optical field transition loss between the waveguide core and the waveguide core-electro-optic material layer composite waveguide core, reducing the insertion loss of the heterogeneous integrated electro-optic modulator, and thus improving the performance of the heterogeneous integrated electro-optic modulator.

[0106] In some alternative embodiments, the first groove exposes the edge regions corresponding to the four sides of the electro-optic material layer 12; the projection of the first groove onto the bonding dielectric layer 23 is a closed annular rectangle;

[0107] The second depression 92 forms a slope structure in the edge region corresponding to the four sides of the electro-optic material layer 12;

[0108] Electrodes 60 are located on both sides of waveguide core 22, at least partially on the surface of dielectric layer 30 corresponding to electro-optic material layer 12.

[0109] In some alternative embodiments, after the step of removing the remaining sacrificial layer 40 and before the step of forming a plurality of electrodes 60 on the side of the dielectric layer 30 opposite to the buried layer 11, the method further includes:

[0110] An upper cladding layer 50 is formed on the side surface of the dielectric layer 30 facing away from the buried layer 11, and the upper cladding layer 50 is also filled with a second groove;

[0111] In the step of forming a plurality of electrodes 60 on the side of the dielectric layer 30 facing away from the buried layer 11, the electrodes 60 are located on the surface of the upper cladding 50 corresponding to the electro-optic material layers 12 on both sides of the waveguide core 22.

[0112] like Figure 2 As shown, the present invention also provides a detailed flowchart of a method for fabricating a heterogeneous integrated electro-optic modulation device, including but not limited to steps S201 to S209.

[0113] Step S201: Provide an electro-optic material unit and a waveguide core 22 wafer; the electro-optic material unit includes a first substrate 10, a buried layer 11, and an electro-optic material layer 12 stacked together, such as... Figure 3 As shown; the waveguide core 22 wafer includes a stacked second substrate 20, a lower cladding layer 21, a waveguide core 22, and a bonding dielectric layer 23. The bonding dielectric layer 23 covers the side surface of the waveguide core 22 facing away from the second substrate 20 and the side surface of the waveguide core 22, as shown. Figure 4 As shown.

[0114] In specific implementation, the materials of the first substrate 10 and the second substrate 20 can be silicon, etc.; the material of the buried layer 11 can be silicon dioxide, etc., with a thickness of 0.1 μm to 5 μm; the electro-optic material layer 12 can be a thin film of a material with electro-optic effect, such as lithium niobate, lithium tantalate, barium titanate, etc., with a thickness of 100 nm to 500 nm and a length of 0.1 mm to 20 mm. The material of the lower cladding layer 21 can be silicon dioxide, etc., with a thickness of 2 μm to 20 μm; the material of the waveguide core 22 can be silicon nitride, silicon, etc.; the material of the bonding dielectric layer 23 can be a single layer or a stack of SiO2, Al2O3, etc., the bonding dielectric layer 23 has a flat surface, and the thickness of the bonding dielectric layer 23 located above the waveguide core 22 is 10 nm to 300 nm.

[0115] Step S202: At least one electro-optic material unit is bonded to the side surface of the bonding dielectric layer 23 facing away from the waveguide core 22, such as... Figure 5A and Figure 5B As shown; the first substrate 10 is removed to form a processing intermediate containing a waveguide core 22 and an electro-optic material layer 12, as shown. Figure 6A and Figure 6B As shown, the projection of the electro-optic material layer 12 onto the bonding dielectric layer 23 partially overlaps with the projection of the waveguide core 22 onto the bonding dielectric layer 23; the projection of the electro-optic material layer 12 onto the bonding dielectric layer 23 is rectangular.

[0116] In step S203, a dielectric layer 30 is formed on the surface of the electro-optic material layer 12 facing away from the bonding dielectric layer 23. The dielectric layer 30 also covers the remaining surface of the bonding dielectric layer 23 not covered by the electro-optic material layer 12 and the side surface of the electro-optic material layer 12, such as... Figure 7 As shown.

[0117] In practice, the deposited dielectric layer 30 covers the surface and sides of the electro-optic material layer 12 and the surface of the bonding dielectric layer 23. The dielectric layer 30 is subjected to CMP process to make the surface of the dielectric layer 30 flat. The material of the dielectric layer 30 can be SiO2, etc., and the thickness of the dielectric layer 30 above the buried layer 11 is 0.5μm to 2μm.

[0118] Step S204: A first groove is formed on the side of the dielectric layer 30 facing away from the electro-optic material layer 12. The first groove penetrates the dielectric layer 30 and the buried layer 11, exposing at least one set of opposite edge regions of the electro-optic material layer 12 and part of the bonding dielectric layer 23. The area of ​​the dielectric layer 30 outside the first groove is the second region. The projection of the waveguide core 22 onto the bonding dielectric layer 23 intersects with the projection of the first groove onto the bonding dielectric layer 23. The projection of the first groove onto the bonding dielectric layer 23 includes at least two parallel rectangles, such as... Figure 8A , Figure 8B and Figure 8C As shown.

[0119] In a specific implementation, the patterned dielectric layer 30 and the buried layer 11 form a first groove that exposes at least one pair of opposing edges of electro-optic material layers 12 along the length of the waveguide core 22, as well as the bonding dielectric layer 23 near the electro-optic material layers 12. The width of the first groove is 20 μm to 1000 μm; the width of the edge region corresponding to each edge of the electro-optic material layer 12 exposed by the first groove is less than or equal to half the width of the first groove, which can be 5 μm to 500 μm, and the width of the edges of each exposed electro-optic material layer 12 can be the same or different.

[0120] In Example 1, such as Figure 8A As shown, the first groove exposes the edge region corresponding to a set of opposite sides of the electro-optic material layer 12; the projection of the waveguide core 22 on the bonding dielectric layer 23 intersects with the projection of the first groove on the bonding dielectric layer 23; the projection of the first groove on the bonding dielectric layer 23 includes two parallel rectangles.

[0121] In Example 2, such as Figure 8B As shown, the first groove exposes the edge regions corresponding to the four sides of the electro-optic material layer 12; the projection of the first groove on the bonding dielectric layer 23 is a closed annular rectangle.

[0122] Step S205: A sacrificial layer 40 is filled into the first groove, and the sacrificial layer 40 also covers the surface of the dielectric layer 30 in the second region; the polishing removal rate of the sacrificial layer 40 is greater than the polishing removal rate of the dielectric layer 30, such as... Figure 9 As shown.

[0123] In practice, the lowest surface of the sacrificial layer 40 is higher than the surface of the dielectric layer 30. The material of the sacrificial layer 40 can be a metal, such as Cu or Al. The polishing removal rate of the sacrificial layer 40 is greater than that of the dielectric layer 30, for example, the ratio of the polishing removal rates of the sacrificial layer 40 to the dielectric layer 30 is 2 to 20.

[0124] Step S206 involves performing a first polishing stage of chemical mechanical polishing on the sacrificial layer 40 to remove the sacrificial layer 40 and part of the dielectric layer 30 in the second region, as well as part of the sacrificial layer 40 within the first groove. A sacrificial layer depression is formed on the surface of the sacrificial layer 40 within the first groove. The thickness of the sacrificial layer 40 gradually decreases from the edge of the first groove towards the center until the depth of the sacrificial layer depression no longer increases, forming a first depression 91. The first depression 91 is a saturated depression. The first polishing removal rate of the sacrificial layer 40 is greater than the polishing removal rate of the dielectric layer 30. Figure 10A , Figure 10B and Figure 10C As shown.

[0125] In practice, as the CMP of the sacrificial layer 40 is carried out, the sacrificial layer 40 above the dielectric layer 30 is first removed, exposing the dielectric layer 30. The dielectric layer 30 and the sacrificial layer 40 come into contact with the polishing pad at the same time. Since the polishing removal rate of the sacrificial layer 40 is faster than that of the dielectric layer 30, and the polishing pad has a certain degree of flexibility, the surface of the polishing pad in contact with the sacrificial layer 40 will deform under pressure, thereby maintaining contact with the sacrificial layer 40 and continuously removing the sacrificial layer 40, creating a depression on the surface of the sacrificial layer 40 (the dielectric layer 30 around the sacrificial layer 40 acts as a support) until the surface of the polishing pad in contact with the sacrificial layer 40 reaches the maximum deformation, and the depression on the surface of the sacrificial layer 40 (relative to the surface of the dielectric layer 30) will also reach the maximum depth (saturation depth), that is, forming the first depression 91.

[0126] In some embodiments, the dielectric layer 30 is made of silicon dioxide, the sacrificial layer 40 is made of copper, and the electro-optic material layer 12 is made of lithium niobate. In the chemical mechanical polishing process, the polishing slurry includes a copper polishing slurry and a hydrogen peroxide oxidant. The mass fraction of hydrogen peroxide in the copper polishing slurry can be 0.1% to 10%, the polishing pressure is 3 psi to 5 psi, the rotation speed of the polishing head is 30 r / min to 120 r / min, the rotation speed of the polishing pad is 30 r / min to 120 r / min, and the flow rate of the polishing slurry is 50 ml / min to 300 ml / min.

[0127] Step S207: The sacrificial layer 40 undergoes a second polishing stage of chemical mechanical polishing, removing a portion of the dielectric layer 30 in the second region, as well as a portion of the sacrificial layer 40 and a portion of the electro-optic material layer 12 within the first groove. The first depression 91 extends to the electro-optic material layer 12, forming a second depression 92. The depth of the second depression 92 gradually decreases from the center to the edge of the first groove. The second depression 92 exposes the bonding dielectric layer 23. The second depression 92 forms a slope structure in the edge region corresponding to at least one pair of opposite edges of the electro-optic material layer 12. The thickness of the slope structure... The slope gradually decreases in the direction away from the center of the electro-optic material layer 12; the projection of the slope structure of the electro-optic material layer 12 onto the bonding dielectric layer 23 intersects with the projection of the waveguide core 22 onto the bonding dielectric layer 23; the second polishing removal rate of the sacrificial layer 40 is equal to the polishing removal rate of the dielectric layer 30; the polishing removal rate of the electro-optic material layer 12 is greater than or equal to the polishing removal rate of the dielectric layer 30; the polishing removal rate of the bonding dielectric layer 23 is not greater than the polishing removal rate of the dielectric layer 30; the depth of the first recess 91 and the depth of the second recess 92 are similar, such as... Figure 11A , Figure 11B and Figure 11C As shown.

[0128] In practice, during the second polishing stage, the depth of the sacrificial layer recess will remain at its saturation depth and will not increase further. That is, the removal rates of the dielectric layer 30 in the second region and the sacrificial layer 40 in the first groove are the same, and their surface heights decrease synchronously. The edge of the electro-optic material layer 12 is gradually exposed and polished using the sacrificial layer recess and / or the bonding dielectric layer 23 (when exposed) as a mask. The thickness gradient of the sacrificial layer 40 gradually propagates to the exposed electro-optic material layer 12, forming a gradually thinning slope structure at the edge region of the electro-optic material layer 12. In some examples, the depth of the first recess 91 and the depth of the second recess 92 are equal.

[0129] In Example 1, such as Figure 11A As shown, the second recess 92 forms a slope structure in the edge region corresponding to a set of opposite sides of the electro-optic material layer 12. The projection of the slope structure on the bonding dielectric layer 23 intersects with the projection of the waveguide core 22 on the bonding dielectric layer 23.

[0130] In Example 2, such as Figure 11B As shown, the second depression 92 forms a slope structure in the edge regions corresponding to the four sides of the electro-optic material layer 12.

[0131] Step S208: Remove the remaining sacrificial layer 40, and form a second groove at the location of the first groove. The second groove penetrates the dielectric layer and exposes the slope structure corresponding to at least two sides of the electro-optic material layer and part of the bonding dielectric layer, such as... Figure 12A , Figure 12B and Figure 12C As shown.

[0132] In Example 1, such as Figure 12A As shown, the second groove exposes a set of opposite sides of the electro-optic material layer 12 corresponding to the slope structure; the projection of the waveguide core 22 on the bonding dielectric layer 23 intersects with the projection of the first groove on the bonding dielectric layer 23; the projection of the second groove on the bonding dielectric layer 23 includes two parallel rectangles.

[0133] In Example 2, such as Figure 12B As shown, the second groove exposes the slope structure corresponding to the four sides of the electro-optic material layer 12; the projection of the second groove on the bonding dielectric layer 23 is a closed annular rectangle.

[0134] In step S209, a plurality of electrodes 60 are formed on the side of the dielectric layer 30 facing away from the electro-optic material layer 12, and the electrodes 60 are located at corresponding positions on both sides of the waveguide core 22.

[0135] In specific implementations, the electrode 60 material can be Au, Cu, Al, etc., the thickness of the electrode 60 is 0.5μm to 2μm, the width of the electrode 60 is 10μm to 200μm, and the spacing between the electrodes 60 is 6μm to 10μm. Preferably, the length of the electrode 60 is entirely within the length range of the uniform thickness portion of the electro-optic material layer 12.

[0136] In Example 1, such as Figure 13A and Figure 13B As shown, the electrode 60 is located on the surface of the dielectric layer 30 corresponding to the electro-optic material layer 12 on both sides of the waveguide core 22.

[0137] In Example 2, such as Figure 14A and Figure 14B As shown, the electrodes 60 are located on both sides of the waveguide core 22, and at least partially on the surface of the dielectric layer 30 corresponding to the electro-optic material layer 12.

[0138] Furthermore, in another method for fabricating a heterogeneous integrated electro-optic modulation device, step S209 includes:

[0139] An upper cladding layer 50 is formed on the side surface of the dielectric layer 30 facing away from the buried layer 11, and the upper cladding layer 50 is also filled with a second groove;

[0140] Multiple electrodes 60 are formed on the side of the upper cladding 50 facing away from the electro-optic material layer 12, and the electrodes 60 are located at corresponding positions on both sides of the waveguide core 22.

[0141] In specific implementation, firstly, an upper cladding layer 50 is deposited, covering the surfaces of the dielectric layer 30, bonding dielectric layer 23, buried layer 11, and electro-optic material layer 12, as well as the sides of the dielectric layer 30, buried layer 11, and electro-optic material layer 12. The upper cladding layer 50 is then planarized. Next, electrodes 60 are formed on the upper cladding layer 50 on both sides of the waveguide core 22 and above the electro-optic material layer 12. The material of the electrodes 60 can be Au, Cu, Al, etc., with a thickness of 0.5 μm to 2 μm, a width of 10 μm to 200 μm, and a spacing of 6 μm to 10 μm. Preferably, the length of the electrodes 60 is entirely within the length of the equal-thickness portion of the electro-optic material layer 12; the material of the upper cladding layer 50 is SiO2, and the thickness of the upper cladding layer 50 above the dielectric layer 30 is 0.1 μm to 2 μm.

[0142] In Example 1, after step S208, the upper cladding layer 50 is first formed, as follows: Figure 15A , Figure 15B and Figure 15C As shown, the upper cladding 50 fills two parallel second grooves and covers the surface of the dielectric layer 30; then, electrodes 60 are formed on the upper cladding 50. The projections of the electrodes 60 onto the bonding dielectric layer 23 are located on both sides of the length direction of the projection of the waveguide core 22 onto the bonding dielectric layer 23, as shown. Figure 16A and Figure 16B As shown.

[0143] In Example 2, the upper cladding layer 50 is first formed, as follows: Figure 17A , Figure 17B and Figure 17CAs shown, the upper cladding 50 fills the second groove with four interconnected sides and covers the surface of the dielectric layer 30; then, an electrode 60 is formed on the upper cladding 50. The projection of the electrode 60 onto the bonding dielectric layer 23 is located on both sides of the length direction of the projection of the waveguide core 22 onto the bonding dielectric layer 23, as shown. Figure 18A and Figure 18B As shown.

[0144] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0145] The above description does not provide detailed explanations of the technical aspects of each layer's patterning, etching, etc. However, those skilled in the art should understand that various technical means can be used to form layers and regions of the desired shape. Furthermore, to form the same structure, those skilled in the art can also design methods that are not entirely identical to those described above. Additionally, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination.

[0146] The above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of protection of the present invention is determined by the scope of the appended claims.

Claims

1. A method for fabricating a heterogeneous integrated electro-optic modulation device, characterized in that, include: A processing intermediate comprising a waveguide core and an electro-optic material layer is formed. The processing intermediate includes a bonding dielectric layer, a waveguide core on one side of the bonding dielectric layer, and an electro-optic material layer on the other side of the bonding dielectric layer. The projection of the electro-optic material layer onto the bonding dielectric layer partially overlaps with the projection of the waveguide core onto the bonding dielectric layer; the bonding dielectric layer also covers the side surface of the waveguide core; A dielectric layer is formed on the side surface of the electro-optic material layer opposite to the bonding dielectric layer, and the dielectric layer also covers the remaining surface of the bonding dielectric layer not covered by the electro-optic material layer and the side surface of the electro-optic material layer; A first groove is formed on the side of the dielectric layer opposite to the electro-optic material layer. The first groove penetrates the dielectric layer and exposes the edge regions corresponding to at least two sides of the electro-optic material layer and a portion of the bonding dielectric layer. The area outside the first groove where the dielectric layer is located is the second region; A sacrificial layer is filled in the first groove; the polishing removal rate of the sacrificial layer is greater than the polishing removal rate of the dielectric layer. The sacrificial layer is subjected to a chemical mechanical polishing process to remove part of the dielectric layer in the second region, as well as part of the sacrificial layer and part of the electro-optic material layer in the first groove. A second depression is formed in the sacrificial layer and electro-optic material layer in the first groove. The second depression forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer. The depth of the second depression gradually decreases from the center to the edge of the first groove. The second depression exposes the bonding dielectric layer. The projection of the slope structure of the electro-optic material layer on the bonding dielectric layer intersects with the projection of the waveguide core on the bonding dielectric layer.

2. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 1, characterized in that, In the step of filling the first groove with a sacrificial layer, the sacrificial layer also covers the surface of the dielectric layer in the second region; The step of performing chemical mechanical polishing on the sacrificial layer further includes: removing the sacrificial layer and part of the dielectric layer in the second region.

3. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 2, characterized in that, The chemical mechanical polishing process includes a first polishing stage and a second polishing stage in sequence. The first polishing stage includes: removing the sacrificial layer and part of the dielectric layer in the second region, as well as part of the sacrificial layer in the first groove, forming a sacrificial layer depression on the surface of the sacrificial layer in the first groove, the thickness of the sacrificial layer gradually decreasing from the edge of the first groove to the center until the depth of the sacrificial layer depression no longer increases, thus forming the first depression; the first polishing removal rate of the sacrificial layer is greater than the polishing removal rate of the dielectric layer. The second polishing stage includes: removing a portion of the dielectric layer in the second region, as well as a portion of the sacrificial layer and a portion of the electro-optic material layer within the first recess, wherein the first recess extends to the electro-optic material layer to form a second recess; the second recess exposes the bonding dielectric layer, and the second recess forms a slope structure in the edge region corresponding to at least two sides of the electro-optic material layer, wherein the thickness of the slope structure gradually decreases along a direction away from the center of the electro-optic material layer; the second polishing removal rate of the sacrificial layer is equal to the polishing removal rate of the dielectric layer.

4. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 3, characterized in that, In the first polishing stage, the first depression is a saturated depression; the depth of the saturated depression is positively correlated with the ratio of the first polishing removal rate of the sacrificial layer to the polishing removal rate of the dielectric layer. In the second polishing stage, the polishing removal rate of the electro-optic material layer is greater than or equal to the polishing removal rate of the dielectric layer; The polishing removal rate of the bonding medium layer is not greater than the polishing removal rate of the medium layer. The depth of the second depression is greater than or equal to the depth of the first depression.

5. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 3, characterized in that, The dielectric layer is made of silicon dioxide, the sacrificial layer is made of copper, and the electro-optic material layer is made of lithium niobate.

6. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 1, characterized in that, In the step of forming the first groove, at least two sides of the electro-optic material layer exposed by the first groove are located on the center line of the first groove; In the step of performing chemical mechanical polishing on the sacrificial layer, the thickness of the resulting slope structure gradually decreases to 0 along the direction away from the center of the electro-optic material layer.

7. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 1, characterized in that, The step of forming a processing intermediate comprising a waveguide core and an electro-optic material layer includes: An electro-optic material unit and a waveguide core wafer are provided; the electro-optic material unit includes a first substrate, a buried layer and an electro-optic material layer stacked together; the waveguide core wafer includes a second substrate, a lower cladding layer, a waveguide core and a bonding dielectric layer stacked together, the bonding dielectric layer covering the side surface of the waveguide core facing away from the second substrate and the side surface of the waveguide core; At least one of the electro-optic material units is bonded to the bonding dielectric layer on the side facing away from the waveguide core, and the first substrate is removed; the projection of the electro-optic material unit on the bonding dielectric layer partially overlaps with the projection of the waveguide core on the bonding dielectric layer; Following the step of performing a chemical mechanical polishing process on the sacrificial layer, the method further includes: Remove the remaining sacrificial layer and form a second groove at the location of the first groove. The second groove penetrates the dielectric layer and exposes the slope structure corresponding to at least two sides of the electro-optic material layer and part of the bonding dielectric layer. Multiple electrodes are formed on the side of the dielectric layer opposite to the electro-optic material layer, and the electrodes are located at corresponding positions on both sides of the waveguide core.

8. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 7, characterized in that, The projection of the electro-optic material layer onto the bonding dielectric layer is rectangular; The first groove penetrates the dielectric layer and the buried layer, and exposes at least one set of opposite edge regions of the electro-optic material layer; the projection of the waveguide core on the bonding dielectric layer intersects with the projection of the first groove on the bonding dielectric layer; the projection of the first groove on the bonding dielectric layer includes at least two parallel rectangles. The second recess forms a slope structure in the edge region corresponding to at least one set of opposite sides of the electro-optic material layer; The electrodes are located at least on the surface of the dielectric layer corresponding to the electro-optic material layers on both sides of the waveguide core.

9. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 8, characterized in that, The first groove exposes the edge regions corresponding to the four sides of the electro-optic material layer; the projection of the first groove onto the bonding dielectric layer is a closed annular rectangle; The second recess forms a slope structure in the edge regions corresponding to the four sides of the electro-optic material layer; The electrodes are located on both sides of the waveguide core, and at least partially on the surface of the dielectric layer corresponding to the electro-optic material layer.

10. The method for fabricating a heterogeneous integrated electro-optic modulation device according to claim 7, characterized in that, After the step of removing the remaining sacrificial layer and before the step of forming multiple electrodes, the following steps are also included: An upper cladding layer is formed on the side surface of the dielectric layer opposite to the buried layer, and the upper cladding layer also fills the second groove; In the step of forming multiple electrodes, the electrodes are located on the upper cladding surfaces corresponding to the electro-optic material layers on both sides of the waveguide core.

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