Method for manufacturing optical element having air gap

Abstract

This method for manufacturing an optical element having an air gap includes the steps of: (a) forming a sacrificial film between a plurality of structures on a substrate, on which the plurality of structures are formed; (b) forming a sealing film on each of the structures and the sacrificial film; and (c) removing the sacrificial film by heating the sacrificial film and permeating the heated sacrificial film through the sealing film.

Description

Method for manufacturing optical element with air gap

[0001] The present disclosure relates to a method for manufacturing an optical element with an air gap.

[0002] Patent Document 1 discloses an optical element with an air gap.

[0003] U.S. Patent Application Publication No. 2022 / 0299677 Specification

[0004] The present disclosure provides a technique for forming a highly accurate air gap in an optical element.

[0005] According to the present disclosure, there is provided a method for manufacturing an optical element with an air gap, comprising: a) a step of forming a sacrificial film between a plurality of the structures on a substrate on which the plurality of structures are formed; b) a step of forming a sealing film on top of each of the structures and the sacrificial film; and c) a step of heating the sacrificial film to remove the sacrificial film by allowing it to permeate through the sealing film.

[0006] The present disclosure provides a technique for forming a highly accurate air gap in an optical element.

[0007] FIG. 1 is a diagram schematically illustrating an optical element with an air gap according to the present embodiment. FIG. 2 is a flowchart illustrating steps of a method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 3 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 4 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 5 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 6 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 7 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 8 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment. FIG. 9 is a cross-sectional view for explaining steps of the method for manufacturing an optical element with an air gap according to the present embodiment.

[0008] The embodiments will be described below with reference to the attached drawings. However, this disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope of the claims as indicated by the claims.

[0009] In addition, regarding the descriptions and drawings of each embodiment, redundant explanations may be omitted by assigning the same or corresponding reference numerals to components having substantially the same or corresponding functional configurations. Furthermore, for ease of understanding, the scale of each part in the drawings may differ from that of the actual parts.

[0010] A method for manufacturing an optical element having an air gap according to this embodiment will now be described. The method for manufacturing an optical element having an air gap according to this embodiment includes a) a step of forming a sacrificial film between the multiple structures on a substrate on which multiple structures are formed. The method for manufacturing an optical element having an air gap according to this embodiment also includes b) a step of forming a sealing film on top of the structures and the sacrificial film, respectively, and c) a step of heating the sacrificial film to remove the sacrificial film by allowing the sealing film to pass through.

[0011] First, we will describe an optical element with an air gap. Figure 1 is a schematic diagram of an optical element 1, which is an example of an optical element with an air gap according to this embodiment.

[0012] The optical element 1 is a so-called metalens. The optical element 1 comprises a substrate 10, a plurality of columnar structures 11, and a sealing member 20.

[0013] The substrate 10 is formed from a transparent material. For example, the substrate 10 is made of glass. When we say "transparent," we are not limited to being transparent to visible light, but may also mean being transparent to infrared light or ultraviolet light, for example. The substrate 10 may be made of amorphous silicon, for example.

[0014] The columnar structure 11 is formed from a transparent material. The columnar structure 11 is provided protruding from the surface 10S of the substrate 10. The columnar structure 11 is formed from, for example, a high refractive index material. The high refractive index material forming the columnar structure 11 is composed of, for example, amorphous silicon, silicon nitride, titanium oxide, etc., and has a refractive index of 1.65 or higher.

[0015] The columnar structure 11 has a columnar shape. The columnar structure 11 is, for example, a cylinder, an elliptical column, or a rectangular prism. If the columnar structure 11 is a rectangular prism, the number of corners is not particularly limited. The height of the columnar structure 11 is, for example, 50 nanometers or more and 2000 nanometers or less. The width of the columnar structure 11 is, for example, 10 nanometers or more and 1000 nanometers or less. The width of the columnar structure 11 may differ at the tip and the base. Also, the columnar structure 11 may protrude diagonally from the substrate 10.

[0016] The columnar structures 11 are arranged based on the optical properties required for the optical element 1. The spacing between the multiple columnar structures 11 may be appropriately determined, for example, within the range of 30 nanometers to 100 nanometers. Furthermore, the spacing between the multiple columnar structures 11 may vary depending on the location.

[0017] An air gap AG is provided between the columnar structures 11. The optical properties of the optical element 1 are determined by the difference in refractive index between the columnar structures 11 and the air gap AG.

[0018] The columnar structure 11 is formed, for example, by etching a layer uniformly formed on the surface 10S of the substrate 10.

[0019] The sealing member 20 protects the substrate 10 and the columnar structures 11. The sealing member 20 also protects the air gap AG from entering with dust and other debris. The sealing member 20 is made of a transparent material. For example, the sealing member 20 is made of silicon dioxide. The sealing member 20 is provided to cover the substrate 10 and the multiple columnar structures 11.

[0020] Next, a method for manufacturing an optical element having an air gap according to this embodiment will be described. Figure 2 is a flowchart showing the steps of the method for manufacturing an optical element having an air gap according to this embodiment. Figures 3 to 9 are cross-sectional views illustrating the steps of the method for manufacturing an optical element having an air gap according to this embodiment. Using Figures 3 to 9, the steps for manufacturing an optical element 1, which is an example of an optical element having an air gap according to this embodiment, will be explained. Figures 3 to 9 are cross-sectional views of the peripheral portion of the optical element 1 or an intermediate optical element before the optical element is completed.

[0021] (Step S10) First, a columnar structure is formed on the substrate. Figure 3 is a cross-sectional view showing an intermediate optical element 1a with a columnar structure 11 formed on the substrate 10. The columnar structure 11 is formed on the surface 10S of the substrate 10. The columnar structure 11 has a cylindrical shape, for example, with height H and diameter D. The columnar structures 11 are arranged in a line, for example, with spacing L. For example, the height H is 520 nanometers, the diameter D is 35 nanometers, and the spacing L is 60 nanometers.

[0022] (Step S20) Next, a sacrificial film is formed on the substrate on which the columnar structure is formed. Figure 4 is a cross-sectional view showing an intermediate optical element 1b on which a sacrificial film 31 is formed on the substrate 10 on which the columnar structure 11 is formed. Multiple monomers that will be used as raw materials for the sacrificial film are deposited on the substrate 10 on which the columnar structure 11 is formed and polymerized to generate a polymer. The sacrificial film 31 is formed by generating the polymer.

[0023] Monomers are deposited so as to fill the spaces between multiple columnar structures 11. For example, by using liquid monomers, multiple monomers can be used to fill the spaces between multiple columnar structures 11. Furthermore, by polymerizing the multiple monomers to form a sacrificial film 31, the columnar structures 11 can be stably held while maintaining their shape by the sacrificial film 31. In addition, the sacrificial film 31 makes it easier to stably form the sealing film 32 described later.

[0024] The sacrificial film 31 is formed, for example, by carrying out a vapor deposition polymerization reaction using isocyanate and amine as raw material monomers to form a polymer of polyurea.

[0025] (Step S30) Next, the substrate on which the sacrificial film is formed is annealed. Figure 5 is a cross-sectional view showing an intermediate optical element 1c obtained by annealing the substrate 10 on which the sacrificial film 31 is formed. When the sacrificial film 31 is formed, voids may be formed in the sacrificial film 31. Therefore, in step S30, the sacrificial film 31 is annealed to become a sacrificial film 31a, thereby suppressing the generation of voids in the sacrificial film 31a.

[0026] For example, if there are voids in the sacrificial film 31, abnormalities may occur in the shape of the air gap AG, the columnar structure 11 may collapse, or the columnar structure 11 may become distorted. In the method for manufacturing an optical element with an air gap according to this embodiment, by annealing the sacrificial film, voids in the sacrificial film can be removed, thereby suppressing abnormalities in the shape of the air gap and columnar structure caused by voids.

[0027] When the sacrificial film 31 is annealed, the thickness of the sacrificial film 31a decreases. Therefore, when annealing the sacrificial film 31, the temperature and time of the annealing process are adjusted.

[0028] (Step S40) Next, a portion of the sacrificial film is removed. Figure 6 is a cross-sectional view showing the intermediate optical element 1d with a portion of the sacrificial film 31a removed. The sacrificial film 31a is removed, for example, by etching. The sacrificial film 31a in the peripheral part of the substrate 10 and the sacrificial film 31a on the upper part of the columnar structure 11 are removed, leaving the sacrificial film 31b between the columnar structures 11. For example, the sacrificial film 31b is removed so that it is about the same length as the upper end of the columnar structure 11, or in a range of 70 nanometers or less, below the upper end of the columnar structure 11. For example, it is preferable that the sacrificial film 31b is 30 to 50 nanometers, particularly about 40 nanometers, below the upper end of the columnar structure 11.

[0029] If a portion of the sacrificial film 31a is not removed, for example, the sealing film 32, described later, may float above the columnar structure 11 and the sacrificial film 31b, or the columnar structure 11 may bend. In the method for manufacturing an optical element with an air gap according to this embodiment, abnormalities such as the floating of the sealing film and the bending of the columnar structure can be suppressed by removing a portion of the upper part of the sacrificial film.

[0030] (Step S50) Next, a sealing film is formed. Figure 7 is a cross-sectional view showing the intermediate optical element 1e on which the sealing film 32 has been formed. The sealing film 32 is formed on the peripheral portion of the substrate 10, the columnar structure 11 and the sacrificial film 31b. The sealing film 32 is, for example, silicon dioxide. The thickness of the sealing film 32 is, for example, 1 nanometer or more and 5 nanometers or less. The thickness of the sealing film 32 is, for example, 2 nanometers.

[0031] The sealing film 32 may be, for example, a low-temperature oxide film, more specifically, a low-temperature oxide film composed of silicon dioxide. By making the sealing film 32 a low-temperature oxide film composed of silicon dioxide, a relatively rough film can be made. By making the sealing film 32 a rough film, the depolymerized sacrificial film can be easily permeated when removing the sacrificial film, which will be described later.

[0032] (Step S60) Next, the sacrificial film is removed. Figure 8 is a cross-sectional view showing the intermediate optical element 1f after the sacrificial film 31b has been removed. The sacrificial film 31b is removed by heating the intermediate optical element 1e. When the sacrificial film 31b is heated, the polymer depolymerizes into raw material monomers, and the depolymerized monomers permeate the sealing film 32 and are removed.

[0033] (Step S70) Next, the sealing member 20 is formed. Figure 8 is a cross-sectional view showing the optical element 1 with the sealing member 20 formed. The sealing member 20 is formed, for example, by depositing the same material as the sealing film 32.

[0034] By following the steps described above, an optical element 1, which is an example of an optical element having an air gap according to this embodiment, is manufactured.

[0035] According to the method for manufacturing an optical element with an air gap in this embodiment, a highly accurate air gap can be formed by suppressing shape abnormalities in the columnar structure.

[0036] Metalenses are formed by nanoimprinting or photolithography. The structure forming the metalens is formed, for example, from a high refractive index material. To protect the structure forming the metalens, it is desirable to seal it with a low refractive index material. As the low refractive index material, it is desirable to seal it with air, which has the lowest refractive index, by forming an air gap.

[0037] In this embodiment, the manufacturing method for an optical element having an air gap can form a highly accurate air gap by using a sacrificial film.

[0038] The method for manufacturing an optical element having an air gap according to the present embodiment disclosed herein should be considered in all respects as illustrative and not restrictive. The above embodiments can be modified and improved in various ways without departing from the scope and spirit of the appended claims. The matters described in the above embodiments can be otherwise configured and combined in a non-consistent manner.

[0039] This application claims priority to Basic Patent Application No. 2025-069008, filed with the Japan Patent Office on April 18, 2025, the entire contents of which are incorporated herein by reference.

[0040] 1 Optical elements 1a, 1b, 1c, 1d, 1e, 1f Intermediate optical elements 10 Substrate 10S Surface 11 Columnar structure 20 Sealing members 31, 31a, 31b Sacrificial film 32 Sealing film AG Air gap

Claims

1. A method for manufacturing an optical element having an air gap, comprising: a) forming a sacrificial film between a plurality of structures on a substrate on which a plurality of structures are formed; b) forming a sealing film on top of each of the structures and the sacrificial film; and c) heating the sacrificial film to remove the sacrificial film by allowing the sealing film to pass through.

2. The method for manufacturing an optical element according to claim 1, wherein the sacrificial film is formed by polymerizing a plurality of monomers.

3. The method for producing an optical element according to claim 2, wherein in step c) above, a polymer obtained by polymerizing a plurality of monomers is depolymerized.

4. The method for producing an optical element according to claim 3, wherein the polymer is polyurea.

5. The method for manufacturing an optical element according to any one of claims 1 to 4, wherein the structure is formed of a high refractive index material with a refractive index of 1.65 or higher.

6. The method for manufacturing an optical element according to claim 5, wherein the high refractive index material is amorphous silicon, silicon nitride, and titanium oxide.

7. A method for manufacturing an optical element according to any one of claims 1 to 4, further comprising a step of annealing the sacrificial film after step a) above.

8. A method for manufacturing an optical element according to any one of claims 1 to 4, further comprising the step of removing a portion of the sacrificial film after step a) above.

9. A method for manufacturing an optical element according to any one of claims 1 to 4, further comprising the step of forming a plurality of the structures on the substrate before step a) above.

10. A method for manufacturing an optical element according to any one of claims 1 to 4, further comprising the step of forming a sealing member after step c) above.

11. The method for manufacturing an optical element according to any one of claims 1 to 4, wherein the sealing film is a low-temperature oxide film.

12. The method for manufacturing an optical element according to claim 11, wherein the sealing film is formed of silicon dioxide.

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