Preparation Method and Structure of Lithium Niobate Device

Abstract

The present invention provides a preparation method and structure of a lithium niobate device. The preparation method first defines a complete unit area and an incomplete unit area. Then, when etching the lithium niobate film, the lithium niobate film below the complete unit area and the incomplete unit area is etched separately. In this way, when etching the lithium niobate film below each unit area, a hard mask layer is used as a mask, and other areas are protected by a photoresist layer. In this way, different etching conditions can be used for etching the lithium niobate film in each unit area to optimize the process, avoiding the problems of low etching flatness at the edge of the wafer, roughness of the wafer edge, and large thickness variation of the lithium niobate sheet caused by the existing two-step mask etching technology. In addition, because lithium niobate wafers are expensive, the preparation method of this embodiment can effectively reduce the development cost of the lithium niobate etching process.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a preparation method and structure of a lithium niobate device. Background Art

[0002] Lithium niobate (LiNbO3, LN) single crystal material, due to its unique optoelectronic, piezoelectric, and ferroelectric properties, has found widespread application in surface acoustic wave devices, electro-optic modulators, piezoelectric sensors, and ferroelectric memories. Electro-optic modulators (EOMs) are tools used to convert electrical signals into optical signals and play a vital role in optical communication networks. For decades, LNO has been used as a platform for commercial EO modulators due to its transparency in the communication band and its strong second-order nonlinear effects. Directly bonding LNO layers to silicon, combining the advantages of both in electro-optical performance and manufacturing processes, has become a hot topic in LNO modulator research.

[0003] However, direct etching of lithium niobate often produces rough etched sidewalls. For example, in standard fluorine-based etching processes, the etched product, lithium fluoride, will deposit on the lithium niobate surface, which not only affects the etching rate but also hinders the continued etching process, resulting in low-quality etched sidewalls. Therefore, a two-step mask etching technology for lithium niobate was proposed. The LN waveguide etched sidewalls produced using this method are comparable to devices manufactured using electron beam lithography. However, a problem with this process is that the etching flatness at the wafer edge needs to be improved. The process results in roughness at the wafer edge and large variations in the thickness of the LN sheet, resulting in the 8mm range around the edge of a 4-inch wafer being considered invalid. In addition, compared with the limits of LN material performance and the uniformity achieved on SOI wafers, the optical loss and film uniformity of the LN waveguides produced by this method still have room for improvement. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a method for preparing a lithium niobate device and its structure, which are used to solve the problems of the two-step mask etching technology for lithium niobate in the prior art, such as low etching flatness at the edge of the wafer, roughness of the wafer edge caused by the process, and large variations in the thickness of the lithium niobate sheet.

[0005] To achieve the above-mentioned and other related objectives, the present invention provides a method for preparing a lithium niobate device, the method comprising:

[0006] Providing a substrate, wherein a lithium niobate thin film is bonded to the substrate to form a stacked structure, and the area of the lithium niobate thin film is smaller than that of the substrate;

[0007] depositing a hard mask layer on the stacked structure;

[0008] forming a photoresist layer on the hard mask layer, and patterning the photoresist layer using a photolithography process to form a photolithography window, wherein the photolithography window is formed in the area where the lithium niobate film is located, and the photolithography window reveals a partially complete unit area and a partially incomplete unit area;

[0009] Etching the hard mask layer based on the photolithography window, etching away the hard mask layer of the partially complete cell area and the partially incomplete cell area to form an etching window;

[0010] Partial exposure is performed to reveal a single complete unit area or the incomplete unit area, and the corresponding lithium niobate film is etched; this step is repeated until the lithium niobate films corresponding to all the complete unit areas or the incomplete unit areas are etched.

[0011] Optionally, the substrate is a high-resistance silicon substrate; and a silicon dioxide layer is formed between the high-resistance silicon substrate and the lithium niobate thin film.

[0012] Optionally, the size of the high-resistance silicon substrate is 8 inches, and the size of the lithium niobate film is 4 inches or 6 inches.

[0013] Furthermore, the thickness of the silicon dioxide layer is 3 μm, and the thickness of the lithium niobate film is 500 nm.

[0014] Optionally, the lithium niobate film is an X-cut lithium niobate film.

[0015] Optionally, the hard mask layer is deposited by a PECVD process, and the material of the hard mask layer is one of silicon dioxide, silicon nitride and amorphous silicon.

[0016] The present invention also provides a lithium niobate device structure, which is prepared by using any of the above-mentioned preparation methods for the lithium niobate device.

[0017] As described above, the preparation method and structure of the lithium niobate device of the present invention first define the complete unit area and the incomplete unit area, and then, when etching the lithium niobate film, the lithium niobate film underneath is etched separately based on the complete unit area and the incomplete unit area. In this way, when etching the lithium niobate film underneath each unit area, the hard mask layer is used as a mask, and other areas are protected by the photoresist layer. In this way, different etching conditions can be used for etching the lithium niobate film in each unit area to optimize the process, thereby avoiding the problems of low etching flatness at the edge of the wafer, roughness of the wafer edge, and large variations in the thickness of the lithium niobate sheet caused by the existing two-step mask etching technology. In addition, because lithium niobate wafers are expensive, the preparation method of this embodiment can effectively reduce the development cost of the lithium niobate etching process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figures 1 to 8 Shown are schematic cross-sectional structures of various steps in the existing two-step mask etching technology for lithium niobate.

[0019] Figure 9 Shown is a schematic flow chart of the method for preparing the lithium niobate device of the present invention.

[0020] Figures 10 to 18 Shown is a schematic structural diagram of each step of the method for preparing a lithium niobate device of the present invention; wherein Figure 11 for Figure 10 A top view of Figure 11 Only the relative position relationship between the substrate and the lithium niobate film is shown; Figure 14 for Figure 15 A top view of the area where the lithium niobate film is located, and Figure 14 The figure shows the relative position relationship between the lithium niobate film and the complete unit area and the incomplete unit area. Figure 15 For the Figure 14 Sectional view along the AA section line.

[0021] Component number description

[0022] 10. Laminated structure

[0023] 11 substrate

[0024] 12 Lithium niobate film

[0025] 13 Silicon dioxide layer

[0026] 14 Hard Mask

[0027] 15 Photoresist layer

[0028] 16 Lithography Window

[0029] 17 Etching Window

[0030] 18 complete unit areas

[0031] 19 Incomplete unit area

[0032] 20 silicon wafers

[0033] 21 Lithium niobate film

[0034] 22 Hard Mask

[0035] 23 Anti-reflective coating

[0036] 24 DUV photoresist layers

[0037] 25 cladding

[0038] Steps S1 to S5 DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] See also Figures 1 to 18 It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components relevant to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed according to actual needs, and the component layout may also be more complex.

[0041] As described in the background technology, lithium niobate waveguides are currently prepared using a two-step mask etching technique. The specific preparation process is as follows: Figures 1 to 8 As shown,

[0042] like Figure 1 and Figure 2 As shown, first, a hard mask layer 22 (eg, SiO2 layer) is deposited on top of a lithium niobate film 21 on a silicon wafer 20 by PECVD, and then an anti-reflective coating 23 and a DUV photoresist layer 24 are sequentially spin-coated; Figure 3 As shown, the DUV photoresist layer 24 is then patterned; Figure 4 As shown, the anti-reflective coating 23 is then etched based on the patterned DUV photoresist layer 24; Figure 5 As shown, the hard mask layer 22 is then etched based on the patterned DUV photoresist layer 24; Figure 6 and Figure 7 As shown, 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 layer of lithium niobate, and the DUV photoresist layer 24, the anti-reflective coating 23 and the hard mask layer 22 are removed; Figure 8 As shown, finally a cladding layer 25 (eg, SiO 2 layer) is deposited by PECVD.

[0043] The etched sidewalls of lithium niobate waveguides produced using this method are comparable to those produced using electron-beam lithography. However, this process has the disadvantage of requiring improved etch flatness at the wafer edge. This process results in roughness at the wafer edge and significant variation in LN sheet thickness, rendering the process ineffective within an 8mm radius around the edge of a 4-inch wafer. Furthermore, compared to the limits of LN material performance and the uniformity achieved on SOI wafers, the optical loss and film uniformity of LN waveguides produced using this method still require improvement.

[0044] Based on the above problems, the inventors proposed a new method for preparing lithium niobate devices, such as Figure 9 As shown, the preparation method comprises the following steps:

[0045] Providing a substrate, on which a lithium niobate film is bonded to form a stacked structure, wherein the area of the lithium niobate film is smaller than that of the substrate;

[0046] depositing a hard mask layer on the stacked structure;

[0047] forming a photoresist layer on the hard mask layer, and patterning the photoresist layer using a photolithography process to form a photolithography window, wherein the photolithography window is formed in the area where the lithium niobate film is located, and the photolithography window reveals a partially complete unit area and a partially incomplete unit area;

[0048] Etching the hard mask layer based on the photolithography window, etching away the hard mask layer of the partially complete cell area and the partially incomplete cell area to form an etching window;

[0049] Partial exposure is performed to reveal a single complete unit area or the incomplete unit area, and the corresponding lithium niobate film is etched; this step is repeated until the lithium niobate films corresponding to all the complete unit areas or the incomplete unit areas are etched.

[0050] By adopting the preparation method of the present embodiment, the complete unit area and the incomplete unit area are first defined. Then, when etching the lithium niobate film, the lithium niobate film underneath is etched separately based on the complete unit area and the incomplete unit area. In this way, when etching the lithium niobate film underneath each unit area, the hard mask layer is used as a mask, and other areas are protected by the photoresist layer. In this way, different etching conditions can be used for etching the lithium niobate film in each unit area to optimize the process, thereby avoiding the problems of low etching flatness at the edge of the wafer, roughness of the wafer edge, and large variations in the thickness of the lithium niobate sheet caused by the existing two-step mask etching technology. In addition, because lithium niobate wafers are expensive, the preparation method of the present embodiment can effectively reduce the development cost of the lithium niobate etching process.

[0051] The following describes a method for preparing a lithium niobate device according to the present invention using a specific example. This example uses a high-resistance silicon substrate and includes forming a silicon dioxide layer on the high-resistance silicon substrate before bonding the lithium niobate thin film to the substrate. The method includes the following steps:

[0052] like Figures 9 to 11 As shown, step S1 is first performed to provide a substrate 11 and bond a lithium niobate film 12 on the substrate 11 to form a stacked structure 10 . The area of the lithium niobate film 12 is smaller than that of the substrate 11 .

[0053] As an example, the size of the substrate 11 is selected to be 8 inches, and the size of the lithium niobate film 12 is selected to be 4 inches or 6 inches. The lithium niobate film 12 is selected to be an X-cut lithium niobate film.

[0054] As an example, the silicon dioxide layer 13 between the substrate 11 and the lithium niobate film 12 is formed by a thermal oxidation process. Preferably, the thickness of the silicon dioxide layer 13 is 3 μm, and the thickness of the lithium niobate film 12 is 500 nm.

[0055] like Figure 9 and Figure 12 As shown, step S2 is then performed to deposit a hard mask layer 14 on the stacked structure 10 .

[0056] As an example, a PECVD process may be used to deposit the hard mask layer 14. The material of the hard mask layer 14 may be selected from silicon dioxide (SiO2), silicon nitride (SiN), or amorphous silicon (a-Si).

[0057] like Figure 9 and Figures 13 to 15 As shown, step S3 is then performed to form a photoresist layer 15 (such as Figure 13 As shown), the photoresist layer 15 is patterned by a photolithography process to form a photolithography window 16 (as shown Figure 15 As shown), the photolithography window 16 is formed in the area where the lithium niobate film 12 is located, and the photolithography window 16 reveals a partially complete unit area 18 and a partially incomplete unit area 19.

[0058] like Figure 9 、 Figure 16 and Figure 17 As shown, step S4 is then performed to etch the hard mask layer 14 based on the photolithography window 16 , and the hard mask layer 14 of the partially complete cell region 18 and the partially incomplete cell region 19 are etched away to form an etching window 17 .

[0059] It should be noted here that after the etching window 17 is formed, the patterned photoresist layer 15 is removed.

[0060] like Figure 9 and Figure 18 As shown, step S5 is finally performed to perform partial exposure so that a single complete unit area 18 or the incomplete unit area 19 is exposed, and the corresponding lithium niobate film 12 is etched; this step is repeated until the lithium niobate film 12 corresponding to all the complete unit areas 18 or the incomplete unit areas 19 is etched.

[0061] Specifically, the partial exposure exposes a single complete unit region 18 or an incomplete unit region 19, and the etching process of the corresponding lithium niobate film 12 is as follows: first, a photoresist layer 15 is spin-coated on the entire structure surface, and then photolithography is performed to form a patterned photoresist layer 15 (such as Figure 18 As shown), the patterned photoresist layer 15 exposes the lithium niobate film 12 under the unit area to be etched, and other places are covered by the photoresist layer 15. Then, the lithium niobate film 12 is etched using the hard mask layer 14 on the unit area as a mask, and finally the photoresist layer 15 is removed.

[0062] Based on the above preparation method, this embodiment further provides a lithium niobate device structure, which is prepared using the above preparation method.

[0063] In summary, the present invention provides a method for preparing a lithium niobate device and its structure. Using the preparation method of the present invention, complete and incomplete cell regions are first defined. Then, when etching the lithium niobate film, the lithium niobate film beneath each complete and incomplete cell region is etched separately based on the complete and incomplete cell regions. Thus, when etching the lithium niobate film beneath each cell region, a hard mask layer is used as a mask, while other regions are protected by a photoresist layer. This allows for different etching conditions to be used for etching the lithium niobate film in each cell region, leading to process optimization and avoiding the problems of low wafer edge flatness, roughness at the wafer edge, and large variations in lithium niobate film thickness caused by existing two-step mask etching techniques. Furthermore, because lithium niobate wafers are expensive, the preparation method of this embodiment can effectively reduce the development cost of the lithium niobate etching process. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A method for preparing a lithium niobate device, characterized in that: The preparation method comprises: Providing a substrate, on which a lithium niobate film is bonded to form a stacked structure, wherein the area of the lithium niobate film is smaller than that of the substrate; depositing a hard mask layer on the stacked structure; forming a photoresist layer on the hard mask layer, and patterning the photoresist layer using a photolithography process to form a photolithography window, wherein the photolithography window is formed in the area where the lithium niobate film is located, and the photolithography window reveals a partially complete unit area and a partially incomplete unit area; Etching the hard mask layer based on the photolithography window, etching away the hard mask layer of the partially complete cell area and the partially incomplete cell area to form an etching window; Partial exposure is performed to reveal a single complete unit area or an incomplete unit area, and the corresponding lithium niobate film is etched; this step is repeated until the lithium niobate films corresponding to all the complete unit areas or the incomplete unit areas are etched. During this process, when etching the lithium niobate film under each unit area to be etched, the hard mask layer is used as a mask, and other unit areas are protected by a photoresist layer. Different etching conditions are used for etching the lithium niobate film under each unit area to be etched.

2. The method for preparing a lithium niobate device according to claim 1, wherein: The substrate is a high-resistance silicon substrate; a silicon dioxide layer is formed between the high-resistance silicon substrate and the lithium niobate film.

3. The method for preparing a lithium niobate device according to claim 2, wherein: The size of the high-resistance silicon substrate is 8 inches, and the size of the lithium niobate film is 4 inches or 6 inches.

4. The method for preparing a lithium niobate device according to claim 2, wherein: The thickness of the silicon dioxide layer is 3 μm, and the thickness of the lithium niobate film is 500 nm.

5. The method for preparing a lithium niobate device according to claim 1, wherein: The lithium niobate film is an X-cut lithium niobate film.

6. The method for preparing a lithium niobate device according to claim 1, wherein: The hard mask layer is deposited by a PECVD process, and the material of the hard mask layer is one of silicon dioxide, silicon nitride and amorphous silicon.

7. A lithium niobate device structure, characterized in that: The lithium niobate device structure is prepared by using the preparation method of the lithium niobate device according to any one of claims 1 to 6.

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