CN115774302A - Preparation method and structure of lithium niobate device - Google Patents
Preparation method and structure of lithium niobate device Download PDFInfo
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- CN115774302A CN115774302A CN202111045217.0A CN202111045217A CN115774302A CN 115774302 A CN115774302 A CN 115774302A CN 202111045217 A CN202111045217 A CN 202111045217A CN 115774302 A CN115774302 A CN 115774302A
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Abstract
The invention provides a preparation method and structure of a lithium niobate device, the preparation method defines the complete unit area and incomplete unit area at first, then when etching the lithium niobate film, the lithium niobate film below the complete unit area and incomplete unit area is etched separately based on the complete unit area and incomplete unit area, thus when etching the lithium niobate film below each unit area, the hard mask layer is used as the mask, other areas are protected by the photoresist layer, thus different etching conditions can be adopted for etching the lithium niobate film of each unit area, process optimization is carried out, and the problems of lower etching flatness at the edge of a wafer, roughness at the edge of the wafer and large thickness change of the lithium niobate sheet caused by the existing two-step mask etching technology are avoided; in addition, because the lithium niobate wafer is expensive, the preparation method of the embodiment can effectively reduce the development cost of the lithium niobate etching process.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a preparation method and a structure of a lithium niobate device.
Background
Lithium niobate (LiNbO) 3 LN) single crystal material has unique characteristics of photoelectricity, piezoelectricity, ferroelectricity and the like, and is widely applied to the fields of surface acoustic wave devices, electrooptical modulators, piezoelectric sensors, ferroelectric memories and the like. Electro-optical modulators are used as a means of converting electrical signals to optical signals and playing an important role in optical communication networks, while lithium niobate has been used for decadesIt has been used as a platform for commercial electro-optic modulators because of its transparency in the communications band and strong second-order nonlinear effects. The lithium niobate layer is directly bonded on the silicon, and the advantages of the lithium niobate layer and the silicon in the electro-optical performance and the manufacturing process are combined, so that the silicon-based optical modulator becomes a hot research of the lithium niobate modulator.
However, when lithium niobate is directly etched, a rough etched sidewall is often generated, for example, in an etching process based on standard fluorine, an etching product lithium fluoride is deposited on the surface of lithium niobate, which not only affects the etching speed, but also hinders the continuation of etching, resulting in a low quality of the etched sidewall. Thus, a two-step mask etching technique for lithium niobate is proposed. The LN waveguide etched side wall manufactured by the method can be compared with a device manufactured by electron beam lithography, but the process has the problems that the etching flatness at the edge of the wafer needs to be improved, the process causes the roughness of the edge of the wafer and the large thickness change of an LN thin plate, and the process causes the ineffectiveness within the range of 8mm at the edge of the 4-inch wafer. In addition, there is room for improvement in the optical loss and film uniformity of LN waveguides fabricated by this method, as compared to the limits of LN material performance, and the uniformity achieved on SOI wafers.
Disclosure of Invention
In view of the above disadvantages of the prior art, an object of the present invention is to provide a method for manufacturing a lithium niobate device and a structure thereof, which are used to solve the problems in the prior art that the etching flatness at the edge of a wafer is low, the process causes roughness at the edge of the wafer, and the thickness of a lithium niobate thin plate changes greatly.
In order to achieve the above objects and other related objects, the present invention provides a method for preparing a lithium niobate device, the method comprising:
providing a substrate, wherein a lithium niobate thin film is bonded on the substrate to form a laminated structure, and the area of the lithium niobate thin film is smaller than that of the substrate;
depositing a hard mask layer on the laminated structure;
forming a photoresist layer on the hard mask layer, and patterning the photoresist layer by adopting a photoetching process to form a photoetching window, wherein the photoetching window is formed in the region where the lithium niobate thin film is located, and the photoetching window exposes a part of complete unit region and a part of incomplete unit region;
etching the hard mask layer based on the photoetching window, and etching off the hard mask layer of the partially complete unit region and the partially incomplete unit region to form an etching window;
carrying out partial exposure to expose a single complete unit area or the incomplete unit area, and etching the corresponding lithium niobate thin film; repeating the steps until all the complete unit areas or the lithium niobate thin films corresponding to the incomplete unit areas are etched.
Optionally, the substrate is a high-resistance silicon substrate; and a silicon dioxide layer is also formed between the high-resistance silicon substrate and the lithium niobate thin film.
Optionally, the size of the high-resistance silicon substrate is 8 inches, and the size of the lithium niobate thin film is 4 inches or 6 inches.
Further, the thickness of the silicon dioxide layer is 3 μm, and the thickness of the lithium niobate thin film is 500nm.
Optionally, the lithium niobate thin film is an X-cut lithium niobate thin film.
Optionally, the hard mask layer is deposited by a PECVD process, and the hard mask layer is made of one of silicon dioxide, silicon nitride and amorphous silicon.
The invention also provides a lithium niobate device structure, which is prepared by adopting any preparation method of the lithium niobate device.
As described above, according to the preparation method and the structure of the lithium niobate device, firstly, the complete unit area and the incomplete unit area are defined, then, when the lithium niobate thin film is etched, the lithium niobate thin film below the complete unit area and the incomplete unit area is independently etched based on the complete unit area and the incomplete unit area, so that when the lithium niobate thin film below each unit area is etched, the hard mask layer is used as a mask, and other areas are protected by the photoresist layer, so that different etching conditions can be adopted for etching the lithium niobate thin film of each unit area, process optimization is carried out, and the problems of low etching flatness at the edge of a wafer, roughness at the edge of the wafer and large thickness change of the lithium niobate thin film caused by the existing two-step mask etching technology are solved; in addition, because the lithium niobate wafer is expensive, the preparation method of the embodiment can effectively reduce the development cost of the lithium niobate etching process.
Drawings
Fig. 1 to 8 are schematic cross-sectional structural diagrams of steps in a conventional two-step mask etching technique for lithium niobate.
Fig. 9 is a flow chart showing a method for manufacturing a lithium niobate device according to the present invention.
Fig. 10 to 18 are schematic structural views presented for respective steps of a method of manufacturing a lithium niobate device of the present invention; wherein fig. 11 is a top view of fig. 10, and fig. 11 shows only the relative positional relationship of the substrate and the lithium niobate thin film; fig. 14 is a plan view of the area where the lithium niobate thin film is located in fig. 15, and fig. 14 shows the relative positional relationship of the lithium niobate thin film with the complete cell area and the incomplete cell area, and fig. 15 is a cross-sectional view taken along the section line AA in fig. 14.
Description of the element reference
10. Laminated structure
11. Substrate and method of manufacturing the same
12. Lithium niobate thin film
13. Silicon dioxide layer
14. Hard mask
15. Photoresist layer
16. Photoetching window
17. Etching window
18. Complete unit area
19. Incomplete unit area
20. Silicon wafer
21. Lithium niobate film
22. Hard mask
23. Anti-reflective coating
24 DUV photoresist layer
25. Cladding layer
S1 to S5
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 18. It should be noted that the drawings provided in the present embodiment are only for schematically illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than being drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of each component in actual implementation can be changed according to actual needs, and the layout of the components may be more complicated.
As described in the background art, the conventional two-step mask etching technique for lithium niobate is used to prepare a lithium niobate waveguide, and the specific preparation process is shown in fig. 1 to 8 and includes:
as shown in fig. 1 and 2, a hard mask layer 22 (e.g., si 0) is first PECVD deposited on top of a lithium niobate film 21 on a silicon wafer 20 2 Layer) and then spin-coating an anti-reflective coating 23 and a DUV photoresist layer 24 in that order; as shown in fig. 3, the DUV photoresist layer 24 is then imaged; as shown in fig. 4, the anti-reflective coating 23 is then etched based on the patterned DUV photoresist layer 24; as shown in fig. 5, the hard mask layer 22 is then etched based on the patterned DUV photoresist layer 24; as shown in fig. 6 and 7, the lithium niobate film 21 is then etched based on the patterned DUV photoresist layer 24 and the hard mask layer 22, leaving a thin lithium niobate layer, and the DUV photoresist layer 24, the anti-reflective coating 23 and the hard mask layer 22 are removed; as shown in FIG. 8, a final PECVD deposition of a cladding layer 25 (e.g., si 0) 2 Layers).
The lithium niobate waveguide etching side wall prepared by the method can be compared with a device manufactured by electron beam lithography, but the process has the problems that the etching flatness at the edge of the wafer needs to be improved, the process causes the roughness of the edge of the wafer and the large thickness change of an LN thin plate, and the process causes the ineffectiveness within the range of 8mm at the edge of the 4-inch wafer. In addition, there is room for improvement in optical loss and film uniformity of LN waveguides prepared by this method, as compared to the limits of LN material performance, and uniformity achieved on SOI wafers.
The inventors have proposed a new method for manufacturing a lithium niobate device based on the above problems, as shown in fig. 9, the method comprising the steps of:
providing a substrate, wherein a lithium niobate thin film is bonded on the substrate to form a laminated structure, and the area of the lithium niobate thin film is smaller than that of the substrate;
depositing a hard mask layer on the laminated structure;
forming a photoresist layer on the hard mask layer, and patterning the photoresist layer by adopting a photoetching process to form a photoetching window, wherein the photoetching window is formed in the region where the lithium niobate thin film is located, and the photoetching window exposes a part of complete unit region and a part of incomplete unit region;
etching the hard mask layer based on the photoetching window, and etching off the hard mask layer of the partially complete unit region and the partially incomplete unit region to form an etching window;
carrying out partial exposure to expose a single complete unit area or the incomplete unit area, and etching the corresponding lithium niobate thin film; repeating the step until all the complete unit areas or the lithium niobate thin films corresponding to the incomplete unit areas are etched.
By adopting the preparation method of the embodiment, firstly, a complete unit area and an incomplete unit area are defined, and then when the lithium niobate thin film is etched, the lithium niobate thin film below the complete unit area and the incomplete unit area is independently etched based on the complete unit area and the incomplete unit area, so that when the lithium niobate thin film below each unit area is etched, the hard mask layer is used as a mask, and other areas are protected by the photoresist layer, therefore, different etching conditions can be adopted for etching the lithium niobate thin film of each unit area, the process optimization is carried out, and the problems of low etching flatness at the edge of a wafer, roughness at the edge of the wafer and large thickness change of the lithium niobate thin film caused by the existing two-step mask etching technology are solved; in addition, because the lithium niobate wafer is expensive, the preparation method of the embodiment can effectively reduce the development cost of the lithium niobate etching process.
The following describes a method for manufacturing a lithium niobate device according to a specific example, where the substrate used in the example is a high-resistance silicon substrate, and a step of forming a silicon dioxide layer on the high-resistance silicon substrate is further included before the lithium niobate thin film is bonded on the high-resistance silicon substrate. The preparation method comprises the following steps:
as shown in fig. 9 to 11, first, step S1 is performed to provide a substrate 11, and a lithium niobate thin film 12 is bonded to the substrate 11 to form a stacked structure 10, where the area of the lithium niobate thin film 12 is smaller than that of the substrate 11.
As an example, the size of the substrate 11 is selected to be 8 inches, and the size of the lithium niobate thin film 12 is selected to be 4 inches or 6 inches. The lithium niobate thin film 12 is selected as an X-cut lithium niobate thin film.
As an example, the silicon oxide layer 13 interposed between the substrate 11 and the lithium niobate thin film 12 is formed using a thermal oxidation process. Preferably, the thickness of the silicon dioxide layer 13 is 3 μm, and the thickness of the lithium niobate thin film 12 is 500nm.
As shown in fig. 9 and 12, a step S2 is performed to deposit a hard mask layer 14 on the stacked structure 10.
As an example, the hard mask layer 14 may be deposited using a PECVD process. The material of the hard mask layer 14 may be selected to be silicon dioxide (SiO) 2 ) Silicon nitride (SiN), or amorphous silicon (a-Si).
As shown in fig. 9 and 13 to 15, step S3 is performed to form a photoresist layer 15 on the hard mask layer 14 (as shown in fig. 13), and a photolithography etching process is used to pattern the photoresist layer 15 to form a photolithography window 16 (as shown in fig. 15), where the photolithography window 16 is formed in the area where the lithium niobate thin film 12 is located, and the photolithography window 16 exposes a partially complete cell region 18 and a partially incomplete cell region 19.
As shown in fig. 9, 16 and 17, step S4 is performed to etch the hard mask layer 14 based on the lithography window 16, and etch away the hard mask layer 14 of the partially complete cell region 18 and the partially incomplete cell region 19, so as to form an etching window 17.
It should be noted that after the etching window 17 is formed, the patterned photoresist layer 15 is removed.
As shown in fig. 9 and 18, step S5 is finally performed to perform partial exposure so as to expose a single complete unit area 18 or the incomplete unit area 19, and etch the corresponding lithium niobate thin film 12; this step is repeated until all of the lithium niobate thin films 12 corresponding to the complete unit areas 18 or the incomplete unit areas 19 are etched.
Specifically, the above partial exposure exposes a single complete unit area 18 or incomplete unit area 19, and the process of etching the lithium niobate thin film 12 corresponding to the partial exposure is as follows: firstly, spin-coating a photoresist layer 15 on the surface of the whole structure, then performing photolithography etching to form a patterned photoresist layer 15 (as shown in fig. 18), wherein the patterned photoresist layer 15 exposes the lithium niobate thin film 12 under the unit region to be etched, and the other places are covered by the photoresist layer 15, then etching the lithium niobate thin film 12 by using the hard mask layer 14 on the unit region as a mask, and finally removing the photoresist layer 15.
Based on the above preparation method, this embodiment also provides a lithium niobate device structure, which is prepared by the preparation method described above.
In summary, the invention provides a preparation method of a lithium niobate device and a structure thereof, and the preparation method comprises the steps of firstly defining a complete unit area and an incomplete unit area, and then etching the lithium niobate thin film below the complete unit area and the incomplete unit area based on the complete unit area and the incomplete unit area when etching the lithium niobate thin film, so that a hard mask layer is used as a mask when etching the lithium niobate thin film below each unit area, and other areas are protected by a photoresist layer, thus different etching conditions can be adopted for etching the lithium niobate thin film of each unit area, process optimization is carried out, and the problems of low etching flatness at the edge of a wafer, roughness at the edge of the wafer and large thickness change of the lithium niobate thin film caused by the existing two-step mask etching technology are avoided; in addition, because the lithium niobate wafer is expensive, the preparation method of the embodiment can effectively reduce the development cost of the lithium niobate etching process. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (7)
1. A preparation method of a lithium niobate device is characterized by comprising the following steps:
providing a substrate, wherein a lithium niobate thin film is bonded on the substrate to form a laminated structure, and the area of the lithium niobate thin film is smaller than that of the substrate;
depositing a hard mask layer on the laminated structure;
forming a photoresist layer on the hard mask layer, and patterning the photoresist layer by adopting a photoetching process to form a photoetching window, wherein the photoetching window is formed in the region where the lithium niobate thin film is located, and the photoetching window exposes a partial complete unit region and a partial incomplete unit region;
etching the hard mask layer based on the photoetching window, and etching off the hard mask layer of the partially complete unit region and the partially incomplete unit region to form an etching window;
carrying out partial exposure to expose a single complete unit area or the incomplete unit area, and etching the corresponding lithium niobate thin film; repeating the steps until all the complete unit areas or the lithium niobate thin films corresponding to the incomplete unit areas are etched.
2. The method for producing a lithium niobate device according to claim 1, characterized in that: the substrate is a high-resistance silicon substrate; and a silicon dioxide layer is also formed between the high-resistance silicon substrate and the lithium niobate thin film.
3. The method for producing a lithium niobate device according to claim 2, characterized in that: the size of the high-resistance silicon substrate is 8 inches, and the size of the lithium niobate thin film is 4 inches or 6 inches.
4. The method for producing a lithium niobate device according to claim 2, characterized in that: the thickness of the silicon dioxide layer is 3 mu m, and the thickness of the lithium niobate thin film is 500nm.
5. The method for producing a lithium niobate device according to claim 1, characterized in that: the lithium niobate thin film is an X-cut lithium niobate thin film.
6. The method for producing a lithium niobate device according to claim 1, characterized in that: and depositing the hard mask layer by adopting a PECVD (plasma enhanced chemical vapor deposition) process, wherein the hard mask layer is made of one of silicon dioxide, silicon nitride and amorphous silicon.
7. A lithium niobate device structure characterized by being produced by the production method of a lithium niobate device according to any one of claims 1 to 6.
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| CN202111045217.0A CN115774302A (en) | 2021-09-07 | 2021-09-07 | Preparation method and structure of lithium niobate device |
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| CN202111045217.0A CN115774302A (en) | 2021-09-07 | 2021-09-07 | Preparation method and structure of lithium niobate device |
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| CN115774302A true CN115774302A (en) | 2023-03-10 |
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