CN115993682A - Manufacturing method of lithium niobate optical waveguide - Google Patents
Manufacturing method of lithium niobate optical waveguide Download PDFInfo
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- CN115993682A CN115993682A CN202211652496.1A CN202211652496A CN115993682A CN 115993682 A CN115993682 A CN 115993682A CN 202211652496 A CN202211652496 A CN 202211652496A CN 115993682 A CN115993682 A CN 115993682A
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Abstract
The invention relates to the technical field of optical communication, and particularly discloses a manufacturing method of a lithium niobate optical waveguide, which comprises the following steps: s1: preparing a lithium niobate wafer, preparing each mask layer and coating photoresist; s2: transferring the optical waveguide pattern on the mask layer to photoresist through a photoetching process; s3: etching the oxide layer by a dry method, detecting etching cut-off and removing photoresist; s4: wet etching is used for cleaning and removing redundant polysilicon; s5: etching the core layer lithium niobate by combining a wet method and a dry method to obtain a lithium niobate optical waveguide; s6: the mask layer and the polysilicon layer on the lithium niobate optical waveguide are removed, and the upper cladding layer is deposited after high-temperature reflux treatment.
Description
Technical Field
The application relates to the technical field of optical communication, and particularly discloses a manufacturing method of a lithium niobate optical waveguide.
Background
Lithium niobate is one of the most potential material platforms in the field of integrated photoelectricity at present, and has the advantages of strong electrooptical effect, larger refractive index, excellent nonlinear optical property and the like. 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 focus of development in this field. The optical waveguide is used as a basic structure of the integrated photoelectric device, and the processing and manufacturing level of the optical waveguide determines whether the overall optical performance of the device can fully play the advantages of lithium niobate.
Since lithium niobate itself has stable chemical and physical properties, its etching process has been a difficulty in this field. At present, the processing and manufacturing methods of lithium niobate optical waveguides are various, mainly comprising wet etching and dry etching, and assisted by chemical mechanical polishing, diamond cutting, femtosecond laser direct writing, focused ion beam milling, bar-shaped load waveguide and other technologies. However, in practice, the problems of solid product deposition, surface cleanliness, side wall roughness and the like still cannot be effectively solved in the etching process of the lithium niobate optical waveguide, and a simple, efficient and low-cost processing and manufacturing method is a core foundation for continuous development and perfection of a lithium niobate material platform;
various existing techniques for processing and manufacturing lithium niobate optical waveguides have characteristics, but a plurality of problems still remain unsolved in the etching process. For example, lithium niobate has a low etching rate due to its stable chemical and physical properties; the combination of fluorine-based gas and argon can effectively accelerate the etching rate, but simultaneously reduces the etching selectivity, and can generate lithium fluoride solid sediment, so that the lithium fluoride solid sediment cannot be effectively removed while the etching process is blocked, and the surface of the optical waveguide is unclean; meanwhile, the etching method using metal chromium and the like as the barrier layer cannot be controlled accurately when the barrier layer is removed, and the oxide mask layer may be underetched before the core layer is etched; in addition, the problem of roughness of the side wall is always plagued by processing and manufacturing of the lithium niobate optical waveguide, the inherent etching technology cannot avoid roughening of the side wall of the optical waveguide, and excessively complicated auxiliary processes like chemical mechanical polishing and the like have a very small effect, and the production cost and redundant process links are increased.
In the invention patent with the patent number of CN202210453489.2, a preparation method of a submicron linewidth ridge type optical waveguide of a lithium niobate film based on a chromium mask is provided. The method utilizes inductively coupled plasma to etch the sample, the etching gas is argon and perfluorobutene, the flow rate is 20-25sccm, the radio frequency power is 50-250W, the etching rate of lithium niobate is 30-60nm/min, the prepared optical waveguide side wall has higher verticality, and the final integrated device has small volume and good light constraint condition. Although the lithium niobate optical waveguide is successfully manufactured by the method, on one hand, the etching rate is not high, and on the other hand, when the chromium etching solution is adopted to clean a chromium mask and an aluminum film remained on a sample, the residual chromium mask and the residual aluminum film can cause the under etching of a mask layer and the inclination angle of the side wall of the optical waveguide to be changed;
in the invention patent with the patent number of CN202111250081.7, a preparation method of a lithium niobate thin film electro-optical modulator is provided by utilizing a dry etching process combining fluorine-based gas and argon. In the method, based on the structure of the traveling wave electrode, the lithium niobate thin film is directly etched to obtain a required waveguide structure, and the etching process comprises ion beam etching, inductive coupling plasma etching and reactive ion etching, so that the etching area is reduced, and meanwhile, the process difficulty and the manufacturing cost are also reduced. Likewise, the problems of surface cleanliness, side wall roughness and the like of the optical waveguide in the etching of the lithium niobate film in the patent of the invention still do not give a reasonable and reliable solution, and the quality of the finally obtained lithium niobate optical waveguide is still not high enough, so that the inventor provides a novel manufacturing method of the lithium niobate optical waveguide in view of the defects of the prior art.
Disclosure of Invention
The invention aims to provide a manufacturing method of a lithium niobate optical waveguide, which combines dry etching and wet etching, can obtain higher etching rate, can effectively remove lithium fluoride solid sediment, ensures the surface cleanliness of the optical waveguide, can prevent an oxide mask layer from being underetched, and can enable the inclination angle of a side wall to be larger and the side wall to be smooth.
In order to achieve the above object, the present invention provides the following basic scheme:
a method of manufacturing a lithium niobate optical waveguide comprising the steps of:
s1: preparing a lithium niobate wafer, preparing each mask layer and coating photoresist;
s2: transferring the optical waveguide pattern on the mask layer to photoresist through a photoetching process;
s3: etching the oxide layer by a dry method, detecting etching cut-off and removing photoresist;
s4: wet etching is used for cleaning and removing redundant polysilicon;
s5: etching the core layer lithium niobate by combining a wet method and a dry method to obtain a lithium niobate optical waveguide;
s6: removing the mask layer and the polysilicon layer on the lithium niobate optical waveguide, and carrying out high-temperature reflux treatment and depositing an upper cladding layer.
The principle and effect of this basic scheme lie in:
1. compared with the prior art, the invention has the advantages that a novel manufacturing method of the lithium niobate optical waveguide is provided for solving the problems of low etching rate, unclean surface, mask undercut, rough side wall and the like in the processing process of the lithium niobate optical waveguide. The method skillfully uses the combination process of etching cut-off detection technology, dry etching and wet etching and high-temperature reflux treatment, and can effectively solve various difficulties in processing and manufacturing lithium niobate optical waveguides. Proved by test production, the result shows that the lithium niobate optical waveguide with high-level optical performance and the corresponding integrated photoelectric device can be obtained by applying the method.
Further, in step S1, the lithium niobate wafer includes a substrate silicon, a lower cladding silicon dioxide, and a core layer lithium niobate, which are sequentially arranged 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-reflection coating, and a photoresist sequentially from bottom to top.
Further, the thickness of the polysilicon layer is 10-50nm, the thickness of the oxide layer is 200-300nm, the thickness of the anti-reflection coating is 10-15nm, and the thickness of the photoresist is 500-600nm.
Further, in step S2, the photolithography process includes exposure and development, and the optical waveguide pattern on the mask layer is transferred onto the photoresist through the photolithography process of exposure and development, so as to obtain the photoresist layer and the anti-reflection coating layer, in which the layout is transferred.
Further, in step S3, the oxide layer is etched by dry etching with fluorine-based gas, and when the polysilicon layer is etched, the detection unit of the etching device performs etching cut-off detection, so that the oxide mask layer is effectively prevented from being under etched, and the photoresist layer and the anti-reflection coating are removed, thereby obtaining the oxide layer.
Further, the wet etching is potassium hydroxide (KOH) solution etching.
Further, in step S5, the core layer lithium niobate is etched by dry etching, and simultaneously, the lithium fluoride solid deposit is removed in combination with wet etching, thereby obtaining the lithium niobate optical waveguide.
Further, in step S5, the dry etching is a mixture gas of fluorine-based gas and argon gas as a main material, and the wet etching is NH 3 、H 2 O 2 And H 2 And the volume ratio of the mixed solution of O to the mixed solution of O is 2:2:1.
Further, in step S5, the dry etching and the wet etching need to be repeated and alternated a plurality of times, until the solid deposit of lithium fluoride is completely removed, and the dry etching and the wet etching can be stopped.
Further, in step S6, the high temperature reflow processing technology is that the lithium niobate optical waveguide is placed in a high temperature reflow processing box, the temperature is 500 ℃ to 600 ℃, and O is filled in the box 2 The high temperature reflux time is 120-150min.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a step diagram showing a method for manufacturing a lithium niobate optical waveguide according to an embodiment of the present application;
FIG. 2 is a schematic flow chart of a method for manufacturing a lithium niobate optical waveguide according to an embodiment of the present application;
fig. 3 shows a schematic cross-sectional structure of a method for manufacturing a lithium niobate optical waveguide according to an embodiment of the present application.
Detailed Description
In order to further describe the technical means and effects adopted by the present invention for achieving the intended purpose, the following detailed description will refer to the specific implementation, structure, characteristics and effects according to the present invention with reference to the accompanying drawings and preferred embodiments.
Reference numerals in the drawings of the specification include: substrate silicon 1, lower cladding silicon dioxide 2, core layer lithium niobate 3, polycrystalline silicon layer 4, oxide layer 5, anti-reflection coating 6, photoresist 7, photoresist layer 8, anti-reflection coating 9, oxide layer 10, polycrystalline silicon layer 11, lithium niobate optical waveguide 12.
Examples are shown in fig. 1, 2 and 3:
a method of manufacturing a lithium niobate optical waveguide comprising the steps of:
s1: preparing a lithium niobate wafer, preparing each mask layer and coating photoresist 7;
specific: a lithium niobate thin film wafer is purchased in advance according to the required thin film thickness, the wafer is composed of a substrate silicon 1, a lower cladding silicon dioxide 2 and a core layer lithium niobate 3, and a polycrystalline silicon layer 4 (10-50 nm), an oxide layer 5 (200-300 nm), an anti-reflection coating 6 (10-15 nm) and a photoresist 7 (500-600 nm) are prepared on the wafer;
in this embodiment, the thickness of the polysilicon layer 4 is 30nm, the thickness of the oxide layer 5 is 250nm, the thickness of the anti-reflection coating 6 is 12nm, and the thickness of the photoresist 7 is 550nm.
In step S1, a mature product of the lithium niobate wafer is available, but only the wafer cannot be processed, and each mask layer, photoresist 7 and the like need to be prepared on the wafer according to specific optical waveguide structures and process links, which is equivalent to preparing for each subsequent step.
After all preparation, the process is the same as part (a) in FIG. 2.
S2: transferring the optical waveguide pattern on the mask layer to the photoresist 7 through a photoetching process;
specific: the photolithography process includes exposure and development, and the optical waveguide pattern on the mask layer is transferred onto the photoresist 7 by the photolithography process of exposure and development, resulting in the photoresist layer 8 and the anti-reflection coating layer 6 to which the layout is transferred, as in the part (b) of fig. 2.
In the present embodiment, the purpose of S2 is: this step is the basic step of the photolithography process in order to transfer the layout-defined optical waveguide structure onto the photoresist 7 for the etching of the oxide layer 5 in the next step.
S3: etching the oxide layer 5 by a dry method, performing etching cut-off detection, and removing the photoresist 7;
specific: in step S3, the oxide layer 5 is etched by dry etching using fluorine-based gas, and when the polysilicon layer 4 is etched, the detection unit of the etching apparatus performs etching stop detection, so that the oxide mask layer is effectively prevented from being under etched, and the photoresist layer 8 and the anti-reflection coating layer 6 are removed, thereby obtaining the oxide layer 5, as in the portion (c) in fig. 2.
In the present embodiment, the purpose of S3: this step is to transfer the structure on the photoresist 7 to the oxide layer 5 and to check the etching process according to the different byproducts of the etching of the polysilicon layer 4.
The reason for S3: the etching stop can effectively prevent the oxide mask layer from being underetched, and is beneficial to ensuring the precision of the optical waveguide structure when the optical waveguide structure is continuously transferred downwards.
S4: wet etching is used for cleaning and removing redundant polysilicon; as in part (d) of fig. 2, in this step, the wet etching is potassium hydroxide (KOH) solution etching.
In the present embodiment, the purpose of S4: this step is to remove the excess polysilicon layer 4 after the etch stop test.
S5: etching the core layer lithium niobate 3 by combining a wet method and a dry method to obtain a lithium niobate optical waveguide 12;
specific: the lithium niobate 3 in the core layer is etched by dry etching (fluorine-based gas and argon), and simultaneously, the lithium fluoride solid sediment is removed by combining wet etching (NH 3, H2O2 and H2O, and the preferred volume ratio is 2:2:1), and the dry etching, the H2O and the H2O are repeatedly and alternately performed for a plurality of times, so that the cleanliness of the surface of the optical waveguide is effectively ensured, and the lithium niobate optical waveguide 12 is obtained, as in part (e) in fig. 2.
In the process, the dry etching and the wet etching need to be repeated and alternated repeatedly until the lithium fluoride solid sediment is completely removed, and the dry etching and the wet etching can be stopped.
In the present embodiment, the purpose of S5: this step is to etch the core layer lithium niobate to obtain an optical waveguide structure.
The reason for S5: this step uses an etching process combining a dry process and a wet process. On one hand, the dry etching is combined, so that the etching rate can be effectively improved, and lithium fluoride solid sediment can be removed; on the other hand, by adopting wet etching, lithium fluoride deposition spots adhered to the surface of the waveguide can be removed well, so that the waveguide has higher surface cleanliness.
S6: the mask layer, polysilicon layer 4, and high temperature reflow process on lithium niobate optical waveguide 12 are removed and the upper cladding layer is deposited.
Specific: the oxide layer 5 and the polysilicon layer 4 are removed, the lithium niobate optical waveguide 12 is subjected to high-temperature reflow treatment, the oxide generated on the side wall is cleaned and removed by hydrofluoric acid, the smoothness of the side wall of the lithium niobate optical waveguide 12 is effectively ensured, and finally, the upper cladding oxide is deposited at low temperature by the experimental PECVD process, in the step S6, the lithium niobate optical waveguide 12 is subjected to high-temperature reflow treatment in a high-temperature reflow treatment box at 500-600 ℃ for filling O2 in the box for 120-150min, and the high-temperature reflow time is the same as that of the part (f) in the figure.
The specific implementation process comprises the following steps: the lithium niobate optical waveguide 12 disclosed in this example was obtained by performing sequential preparation according to the steps of fig. 2 and 1, and fig. 3 is a sectional view of the prepared lithium niobate optical waveguide 12.
In the present embodiment, the purpose of S6: the step is to remove the redundant mask layers on the optical waveguide after etching and deposit the upper cladding, and in addition, the high-temperature reflow treatment is to solve the problem of the roughness of the side wall of the optical waveguide.
The reason for S6: the high-temperature reflow process is adopted because various peaks and bulges on the side wall of the optical waveguide can be oxidized by treating the optical waveguide in an oxygen environment for a period of time at a certain temperature, and the oxidized structures can be effectively removed by further cleaning with hydrofluoric acid, so that the side wall of the optical waveguide with higher smoothness is obtained.
The method aims to provide a manufacturing method of a lithium niobate optical waveguide 12, which combines dry etching and wet etching, can obtain higher etching rate, can effectively remove lithium fluoride solid sediment, can ensure the surface cleanliness of the optical waveguide, can prevent an oxide mask layer from being underetched, and can enable the inclination angle of a side wall to be larger and the side wall to be smooth.
The present invention is not limited to the above embodiments, but is capable of modification and variation in detail, and other modifications and variations can be made by those skilled in the art without departing from the scope of the present invention.
Claims (10)
1. A method of manufacturing a lithium niobate optical waveguide, characterized by: the method comprises the following steps:
s1: preparing a lithium niobate wafer, preparing each mask layer and coating photoresist;
s2: transferring the optical waveguide pattern on the mask layer to photoresist through a photoetching process;
s3: etching the oxide layer by a dry method, detecting etching cut-off and removing photoresist;
s4: wet etching is used for cleaning and removing redundant polysilicon;
s5: etching the core layer lithium niobate by combining a wet method and a dry method to obtain a lithium niobate optical waveguide;
s6: removing the mask layer and the polysilicon layer on the lithium niobate optical waveguide, and carrying out high-temperature reflux treatment and depositing an upper cladding layer.
2. The method of manufacturing a lithium niobate optical waveguide according to claim 1, wherein in step S1, the lithium niobate wafer comprises a substrate silicon, a lower cladding silicon oxide, and a core layer lithium niobate, the substrate silicon, the lower cladding silicon oxide, and the core layer lithium niobate are arranged in this order from bottom to top, and a mask layer is prepared on the upper surface of the lithium niobate wafer, the mask layer comprising a polysilicon layer, an oxide layer, an anti-reflection coating, and a photoresist in this order from bottom to top.
3. The method of manufacturing a lithium niobate optical waveguide according to claim 2, wherein the thickness of the polysilicon layer is 10 to 50nm, the thickness of the oxide layer is 200 to 300nm, the thickness of the anti-reflection coating layer is 10 to 15nm, and the thickness of the photoresist is 500 to 600nm.
4. The method according to claim 2, wherein in step S2, the photolithography process includes exposure and development, and the pattern of the optical waveguide on the mask layer is transferred onto the photoresist by the photolithography process of exposure and development, so as to obtain the photoresist layer and the anti-reflection coating layer to which the layout is transferred.
5. The method of manufacturing a lithium niobate optical waveguide according to claim 4, wherein in step S3, the oxide layer is etched by dry etching using fluorine-based gas, and when the polysilicon layer is etched, the etching stop detection is performed by a detection unit of the etching apparatus, so that the oxide mask layer is effectively prevented from being underetched, and the photoresist layer and the anti-reflection coating are removed, thereby obtaining the oxide layer.
6. The method of manufacturing a lithium niobate optical waveguide according to claim 1, wherein in step S4, the wet etching is potassium hydroxide (KOH) solution etching.
7. The method of manufacturing a lithium niobate optical waveguide according to claim 2, wherein in step S5, the core layer lithium niobate is etched by dry etching, and the lithium fluoride solid deposit is removed in combination with wet etching, to obtain the lithium niobate optical waveguide.
8. The method for manufacturing a lithium niobate optical waveguide according to claim 7, wherein in step S5, the dry method is performedEtching is mainly performed by using mixed gas of fluorine-based gas and argon gas, and wet etching is NH 3 、H 2 O 2 And H 2 And the volume ratio of the mixed solution of O to the mixed solution of O is 2:2:1.
9. A method of manufacturing a lithium niobate optical waveguide according to any of claims 7 or 8, wherein in step S5, the dry etching and the wet etching are repeated and alternately performed a plurality of times until the solid deposit of lithium fluoride is completely removed, and the dry etching and the wet etching are stopped.
10. The method for manufacturing a lithium niobate optical waveguide according to claim 1, wherein in step S6, the high-temperature reflow treatment process is performed on the lithium niobate optical waveguide in a high-temperature reflow treatment tank at 500 ℃ to 600 ℃ and O is filled in the tank 2 The high temperature reflux time is 120-150min.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202211652496.1A CN115993682A (en) | 2022-12-22 | 2022-12-22 | Manufacturing method of lithium niobate optical waveguide |
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| CN202211652496.1A CN115993682A (en) | 2022-12-22 | 2022-12-22 | Manufacturing method of lithium niobate optical waveguide |
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