A method for manufacturing lithium niobate optical waveguide

Abstract

The invention relates to the field of optical communication technology, and specifically discloses a method for manufacturing a lithium niobate optical waveguide, comprising the following steps: S1: preparing a lithium niobate wafer, preparing each mask layer and coating a photoresist; S2: transferring an optical waveguide pattern on the mask layer to the photoresist through a photolithography process; S3: dry etching an oxide layer, performing etching cutoff detection, and removing the photoresist; S4: cleaning and removing excess polysilicon by wet etching; S5: etching a core layer of lithium niobate by a combination of wet and dry methods to obtain a lithium niobate optical waveguide; S6: removing the mask layer and the polysilicon layer on the lithium niobate optical waveguide, performing a high-temperature reflow treatment, and depositing an upper cladding layer. The method combines dry etching and wet etching to obtain a higher etching rate.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and specifically discloses a method for manufacturing a lithium niobate optical waveguide. Background Art

[0002] As one of the most promising material platforms in the field of integrated optoelectronics, lithium niobate has the advantages of strong electro-optical effect, large refractive index and excellent nonlinear optical properties. The miniaturization and integration of devices such as high-speed electro-optical modulators, optical frequency combs and nonlinear optical frequency converters based on lithium niobate thin films are currently the development focus of this field. As the basic structure of such integrated optoelectronic devices, the processing and manufacturing level of optical waveguides determines whether the overall optical performance of the device can give full play to the advantages of lithium niobate.

[0003] Since lithium niobate itself has stable chemical and physical properties, its etching process has always been a difficult point in this field. At present, there are various processing and manufacturing methods for lithium niobate optical waveguides, mainly wet etching and dry etching, supplemented by chemical mechanical polishing, diamond cutting, femtosecond laser direct writing, focused ion beam milling and strip load waveguide and other technologies. However, in fact, the lithium niobate optical waveguide etching process still cannot effectively solve the problems of solid product deposition, surface cleanliness and side wall roughness. Simple, efficient and low-cost processing and manufacturing methods are the core foundation for the continuous development and improvement of the lithium niobate material platform;

[0004] Although the existing technologies for processing and manufacturing lithium niobate optical waveguides have their own characteristics, there are still many problems that have not been completely solved in the etching process. For example, due to the stable chemical and physical properties of lithium niobate itself, its etching rate is low; the combination of fluorine-based gas and argon gas can effectively accelerate the etching rate, but at the same time it reduces the etching selectivity and generates lithium fluoride solid deposits, which hinder the etching process and cannot be effectively removed, resulting in an unclean optical waveguide surface; at the same time, the etching method using metal chromium as a barrier layer cannot be accurately controlled when removing the barrier layer, which may cause the oxide mask layer to be drilled before the core layer is etched; in addition, the roughness problem of the sidewall has always plagued the processing and manufacturing of lithium niobate optical waveguides. The inherent etching technology cannot prevent the sidewalls of the optical waveguide from becoming rough, and overly cumbersome auxiliary processes such as chemical mechanical polishing not only have little effect, but also increase production costs and redundant process links.

[0005] In the invention patent with patent number CN202210453489.2, a method for preparing a submicron linewidth ridge-type optical waveguide of lithium niobate film based on a chromium mask is given. This method uses inductively coupled plasma to etch the sample. The etching gas is argon and perfluorobutene. The flow rate is 20-25sccm, the RF power is 50-250W, and the etching rate of lithium niobate is 30-60nm / min. The side wall of the prepared optical waveguide has a high verticality, and the final integrated device is small in size and has good optical confinement conditions. Although the method in this invention successfully manufactured a lithium niobate optical waveguide, on the one hand, its etching rate is not high. On the other hand, when the chromium etching solution is used to clean the residual chromium mask and aluminum film on the sample, it may cause drilling of the mask layer and change the inclination angle of the optical waveguide side wall;

[0006] In the invention patent with patent number CN202111250081.7, a dry etching process combining fluorine-based gas and argon gas is used to provide a method for preparing a lithium niobate thin film electro-optical modulator. In this method, based on the structure of the traveling wave electrode, the lithium niobate film is directly etched to obtain the required waveguide structure. The etching process is ion beam etching, inductively coupled plasma etching and reactive ion etching, which reduces the etching area while also reducing the process difficulty and manufacturing cost. Similarly, this invention patent still does not provide a reasonable and reliable solution to the problems of optical waveguide surface cleanliness and side wall roughness in the etching of lithium niobate film. The quality of the lithium niobate optical waveguide finally obtained is still not high enough. In view of the defects of the prior art, the inventor proposes a new method for manufacturing lithium niobate optical waveguides. Summary of the invention

[0007] The object of the present invention is to provide a method for manufacturing a lithium niobate optical waveguide, which combines dry etching and wet etching, can obtain a higher etching rate, can effectively remove lithium fluoride solid deposits and ensure the surface cleanliness of the optical waveguide, can prevent the oxide mask layer from being etched, and can make the side wall inclination angle larger and the side wall smoother.

[0008] In order to achieve the above object, the present invention provides the following basic scheme:

[0009] A method for manufacturing a lithium niobate optical waveguide comprises the following steps:

[0010] S1: prepare lithium niobate wafer, prepare each mask layer and apply photoresist;

[0011] S2: transferring the optical waveguide pattern on the mask layer to the photoresist through a photolithography process;

[0012] S3: dry-etching the oxide layer, performing etching cutoff detection, and removing the photoresist;

[0013] S4: Clean and remove excess polysilicon by wet etching;

[0014] S5: Etch the core layer of lithium niobate by combining wet and dry methods to obtain lithium niobate optical waveguide;

[0015] S6: remove the mask layer and polysilicon layer on the lithium niobate optical waveguide, perform high-temperature reflow treatment, and then deposit an upper cladding layer.

[0016] The principles and effects of this basic solution are:

[0017] 1. Compared with the prior art, the advantage of the present invention is that a new method for manufacturing lithium niobate optical waveguides is proposed to solve the problems of low etching rate, unclean surface, mask drilling and rough sidewalls in the processing of lithium niobate optical waveguides. The method cleverly uses etching cutoff detection technology, a combination of dry etching and wet etching, and high-temperature reflow treatment to effectively solve various problems faced in the processing and manufacturing of lithium niobate optical waveguides. Through trial production verification, the results show that the method can be used to obtain lithium niobate optical waveguides with high optical performance and corresponding integrated optoelectronic devices.

[0018] Further, in step S1, the lithium niobate wafer includes a substrate silicon, a lower cladding silicon dioxide and a core layer of lithium niobate, the substrate silicon, the lower cladding silicon dioxide and the core layer of lithium niobate are arranged in sequence from bottom to top, and a mask layer is prepared on the upper surface of the lithium niobate wafer, and the mask layer includes a polysilicon layer, an oxide layer, an anti-reflective coating and a photoresist in sequence from bottom to top.

[0019] Furthermore, the thickness of the polysilicon layer is 10-50 nm, the thickness of the oxide layer is 200-300 nm, the thickness of the anti-reflective coating is 10-15 nm, and the thickness of the photoresist is 500-600 nm.

[0020] Furthermore, in step S2, the photolithography process includes exposure and development, and the optical waveguide pattern on the mask layer is transferred to the photoresist through the photolithography process of exposure and development to obtain a photoresist layer and an anti-reflective coating layer to which the pattern is transferred.

[0021] Further, in step S3, the oxide layer is etched by dry etching with fluorine-based gas, and when etching to the polysilicon layer, the detection unit of the etching equipment performs etching cutoff detection to effectively prevent the oxide mask layer from being drilled, remove the photoresist layer and the anti-reflective coating, and obtain the oxide layer.

[0022] Furthermore, the wet etching is potassium hydroxide (KOH) solution etching.

[0023] Furthermore, in step S5, the core layer of lithium niobate is etched by dry etching, and the lithium fluoride solid deposit is removed by wet etching to obtain a lithium niobate optical waveguide.

[0024] Further, in step S5, the dry etching is dominated by a mixture of fluorine-based gas and argon gas, and the wet etching is dominated by NH 3 , H 2 O 2 and H 2 O mixed solution, the volume ratio of the three is 2:2:1.

[0025] Furthermore, in step S5, dry etching and wet etching need to be performed repeatedly and alternately for multiple times until the lithium fluoride solid deposits are completely removed, and then the dry etching and wet etching can be stopped.

[0026] Further, in step S6, the lithium niobate optical waveguide is subjected to a high temperature reflow treatment process by placing it in a high temperature reflow treatment box at a temperature of 500°C-600°C and filling the box with O 2 , high temperature reflux time is 120-150min. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A step diagram of a method for manufacturing a lithium niobate optical waveguide proposed in an embodiment of the present application is shown;

[0029] Figure 2 A schematic diagram of a process for manufacturing a lithium niobate optical waveguide proposed in an embodiment of the present application is shown;

[0030] Figure 3 A schematic cross-sectional structure diagram of a method for manufacturing a lithium niobate optical waveguide proposed in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0032] The figure marks in the drawings of the specification include: substrate silicon 1, lower cladding silicon dioxide 2, core layer lithium niobate 3, polysilicon layer 4, oxide layer 5, anti-reflective coating 6, photoresist 7, photoresist layer 8, anti-reflective coating 9, oxide layer 10, polysilicon layer 11, lithium niobate optical waveguide 12.

[0033] Implementation example Figure 1 , Figure 2 and Figure 3 As shown:

[0034] A method for manufacturing a lithium niobate optical waveguide comprises the following steps:

[0035] S1: preparing a lithium niobate wafer, preparing each mask layer and coating a photoresist 7;

[0036] Specifically: lithium niobate thin film wafers are purchased in advance according to the required film thickness. The wafers are composed of substrate silicon 1, lower cladding silicon dioxide 2 and core lithium niobate 3. Polysilicon layer 4 (10-50nm), oxide layer 5 (200-300nm), anti-reflective coating 6 (10-15nm) and photoresist 7 (500-600nm) are prepared on the wafers;

[0037] In this embodiment, the thickness of the polysilicon layer 4 is 30 nm, the thickness of the oxide layer 5 is 250 nm, the thickness of the anti-reflective coating 6 is 12 nm, and the thickness of the photoresist 7 is 550 nm.

[0038] In step S1, in this step, lithium niobate wafers are mature products that can be purchased, but only the wafers cannot be processed. It is necessary to prepare various mask layers and photoresists 7 on the wafers according to the specific optical waveguide structure and process steps, which is equivalent to preparing for the subsequent steps.

[0039] After all preparations are completed, Figure 2 Same as part (a).

[0040] S2: transferring the optical waveguide pattern on the mask layer to the photoresist 7 through a photolithography process;

[0041] Specifically: the photolithography process includes exposure and development, and the optical waveguide pattern on the mask layer is transferred to the photoresist 7 through the exposure and development photolithography process to obtain the photoresist layer 8 and the anti-reflection coating 6 with the transferred pattern, just like Figure 2 Same as part (b).

[0042] In this embodiment, the purpose of S2 is as follows: This step is a basic step in the photolithography process, which is to transfer the optical waveguide structure defined on the layout to the photoresist 7 for etching the oxide layer 5 in the next step.

[0043] S3: dry-etching the oxide layer 5 and performing etching cutoff detection, and removing the photoresist 7;

[0044] Specifically: in step S3, the oxide layer 5 is etched by dry etching with fluorine-based gas, and when the etching reaches the polysilicon layer 4, the detection unit of the etching equipment performs etching cutoff detection to effectively prevent the oxide mask layer from being etched, remove the photoresist layer 8 and the anti-reflective coating 6, and obtain the oxide layer 5, just like Figure 2 Same as part (c).

[0045] In this embodiment, the purpose of S3 is to transfer the structure on the photoresist 7 to the oxide layer 5 and to perform a cutoff detection on the etching process according to different by-products when the polysilicon layer 4 is etched.

[0046] Reason for S3: Etching cutoff can effectively prevent the oxide mask layer from being etched, which is beneficial to ensure the accuracy of the optical waveguide structure when it continues to transfer downward.

[0047] S4: Clean and remove excess polysilicon by wet etching; Figure 2 The same as part (d), in this step, the wet etching is potassium hydroxide (KOH) solution etching.

[0048] In this embodiment, the purpose of S4 is to remove the redundant polysilicon layer 4 after the etching cut-off detection.

[0049] S5: etching the core layer lithium niobate 3 by combining wet and dry methods to obtain a lithium niobate optical waveguide 12;

[0050] Specifically, the core layer lithium niobate 3 is etched by dry etching (fluorine-based gas and argon gas), and the lithium fluoride solid deposit is removed by wet etching (NH3, H2O2, H2O, preferably in a volume ratio of 2:2:1). The two are repeated and repeated multiple times to effectively ensure the cleanliness of the optical waveguide surface, and the lithium niobate optical waveguide 12 is obtained. Figure 2 Part (e) is the same.

[0051] In this process, dry etching and wet etching need to be repeated and performed alternately many times until the lithium fluoride solid deposits are completely removed and then the dry etching and wet etching can be stopped.

[0052] In this embodiment, the purpose of S5 is to etch the core layer of lithium niobate to obtain an optical waveguide structure.

[0053] Reason for S5: This step uses a combination of dry and wet etching processes. On the one hand, the combination of dry etching can effectively increase the etching rate and remove lithium fluoride solid deposits; on the other hand, wet etching can better remove lithium fluoride deposits attached to the waveguide surface, so that the waveguide has a higher surface cleanliness.

[0054] S6: removing the mask layer and the polysilicon layer 4 on the lithium niobate optical waveguide 12, performing a high-temperature reflow treatment, and then depositing an upper cladding layer.

[0055] Specifically: remove the oxide layer 5 and the polysilicon layer 4, perform high-temperature reflow treatment on the lithium niobate optical waveguide 12, use hydrofluoric acid to clean and remove the oxide generated on the side wall, effectively ensure the smoothness of the side wall of the lithium niobate optical waveguide 12, and finally experiment with the PECVD process to deposit the upper cladding oxide at low temperature. In step S6, the lithium niobate optical waveguide 12 is subjected to high-temperature reflow treatment by placing it in a high-temperature reflow treatment box at a temperature of 500°C-600°C, filling the box with O2, and the high-temperature reflow time is 120-150min, as shown in FIG. Figure 2 Part (f) is the same.

[0056] Specific implementation process: according to Figure 2 and Figure 1 The lithium niobate optical waveguide 12 disclosed in this embodiment can be obtained by sequentially preparing the steps of Figure 3 FIG. 1 is a cross-sectional view of the prepared lithium niobate optical waveguide 12 .

[0057] In this embodiment, the purpose of S6 is to remove the redundant mask layers on the optical waveguide after etching and deposit the upper cladding layer. In addition, the high temperature reflow treatment is to solve the problem of roughness of the side wall of the optical waveguide.

[0058] Reason for S6: The high-temperature reflow process is used because the various peaks and protrusions on the side wall of the optical waveguide can be oxidized by treating them in an oxygen environment at a certain temperature for a period of time. Further cleaning with hydrofluoric acid can effectively remove these oxidized structures to obtain a smoother side wall of the optical waveguide.

[0059] The purpose of this method is to provide a method for manufacturing a lithium niobate optical waveguide 12, which combines dry etching and wet etching, can obtain a higher etching rate, can effectively remove lithium fluoride solid deposits and ensure the surface cleanliness of the optical waveguide, can prevent the oxide mask layer from being etched, and can make the side wall inclination angle larger and the side wall smoother.

[0060] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for manufacturing a lithium niobate optical waveguide, characterized in that: The following steps are involved: S1: prepare lithium niobate wafer, prepare each mask layer and apply photoresist; The lithium niobate wafer comprises a substrate silicon, a lower cladding silicon dioxide and a core lithium niobate, wherein the substrate silicon, the lower cladding silicon dioxide and the core lithium niobate are arranged in sequence from bottom to top, and a mask layer is prepared on the upper surface of the lithium niobate wafer, wherein the mask layer comprises a polysilicon layer, an oxide layer, an anti-reflective coating and a photoresist in sequence from bottom to top; S2: transferring the optical waveguide pattern on the mask layer to the photoresist through a photolithography process; S3: dry-etching the oxide layer, performing etching cutoff detection, and removing the photoresist; In step S3, the oxide layer is etched by dry etching with fluorine-based gas, and when etching reaches the polysilicon layer, an etching cutoff detection is performed by a detection unit of the etching equipment to effectively prevent the oxide mask layer from being etched, remove the photoresist layer and the anti-reflective coating, and obtain the oxide layer; S4: Clean and remove excess polysilicon by wet etching; S5: Etch the core layer of lithium niobate by combining wet and dry methods to obtain lithium niobate optical waveguide; S6: remove the mask layer and polysilicon layer on the lithium niobate optical waveguide, perform high-temperature reflow treatment, and then deposit an upper cladding layer.

2. The method for manufacturing a lithium niobate optical waveguide according to claim 1, characterized in that: The thickness of the polysilicon layer is 10-50 nm, the thickness of the oxide layer is 200-300 nm, the thickness of the anti-reflective coating is 10-15 nm, and the thickness of the photoresist is 500-600 nm.

3. The method for manufacturing a lithium niobate optical waveguide according to claim 2, characterized in that: In step S2, the photolithography process includes exposure and development, and the optical waveguide pattern on the mask layer is transferred to the photoresist through the photolithography process of exposure and development to obtain a photoresist layer with the transferred pattern and an anti-reflective coating.

4. The method for manufacturing a lithium niobate optical waveguide according to claim 1, characterized in that: In step S4 , the wet etching is etching with a potassium hydroxide (KOH) solution.

5. The method for manufacturing a lithium niobate optical waveguide according to claim 1, characterized in that: In step S5, the core layer of lithium niobate is etched by dry etching, and the lithium fluoride solid deposit is removed by wet etching to obtain a lithium niobate optical waveguide.

6. The method for manufacturing a lithium niobate optical waveguide according to claim 1, characterized in that: In step S5, the dry etching is dominated by a mixed gas of fluorine-based gas and argon gas, and the wet etching is a mixed solution of NH3, H2O2 and H2O, and the volume ratio of the three is 2:2:

1.

7. A method for manufacturing a lithium niobate optical waveguide according to claim 5 or 6, characterized in that: In step S5, dry etching and wet etching need to be performed repeatedly and alternately for multiple times until the lithium fluoride solid deposits are completely removed, and then the dry etching and wet etching can be stopped.

8. The method for manufacturing a lithium niobate optical waveguide according to claim 1, characterized in that: In step S6, the lithium niobate optical waveguide is subjected to a high temperature reflow treatment process by placing it in a high temperature reflow treatment box at a temperature of 500° C.-600° C., the box is filled with O2, and the high temperature reflow time is 120-150 minutes.

Images