A GaAs / GaN-based two-dimensional hole photonic crystal material based on a holographic exposure system, a preparation method and application thereof

Abstract

The application relates to the field of semiconductor optoelectronic technology, in particular to a GaAs / GaN-based two-dimensional hole-type photonic crystal material based on a holographic exposure system and a preparation method and application thereof. The material adopts a holographic exposure system double-exposure method to prepare a photonic crystal grid pattern on photoresist, adopts a dry etching composite mask to perform photonic crystal grid pattern transfer, and obtains a two-dimensional hole-type photonic crystal material based on hard mask pattern dry etching. The material solves a series of problems such as different photoresist pattern thicknesses obtained by the holographic exposure system and inability to deep etch, and greatly reduces the preparation difficulty and preparation cost.

Description

Technical Field

[0001] This application relates to the field of semiconductor optoelectronic technology, and more specifically, to a GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system, its preparation method, and its application. Background Technology

[0002] The theory of photonic crystals began to develop in the last century. Photonic crystals are formed by the periodic combination of materials with different dielectric constants, and there are two types: aperture photonic crystals and columnar photonic crystals. By adjusting parameters such as lattice constant and lattice type, both types of photonic crystals can generate photonic band gaps. However, the generated photonic band gaps are different. Columnar photonic crystals tend to generate TM polarized band gaps, while aperture photonic crystals tend to generate TE polarized band gaps. The photonic localization effects brought about by lattice defects also differ. Therefore, both types of photonic crystals have wide applications in various fields. In recent years, due to the combination of photonic crystals with semiconductor lasers and their application in optical communication technology, the theoretical analysis and experimental research of photonic crystal materials have received high attention from scholars around the world.

[0003] The properties of photonic crystals are highly sensitive to changes in their structural parameters, thus requiring high dimensional accuracy in fabrication. Currently, commonly used photonic crystal manufacturing methods include electron beam lithography and nanoimprint lithography. While these methods produce photonic crystals with good morphology, they are costly and inefficient, hindering the fabrication of large-area semiconductor nanostructure arrays and large-scale industrialization. Holographic exposure systems, however, significantly reduce production costs due to their unique maskless exposure mechanism. Through proper optical path design, large-area exposure can be achieved, making large-scale fabrication of structural arrays possible.

[0004] Holographic exposure systems use bright and dark fringes generated by the interference of two coherent beams to expose photoresist. Due to the interference, the two beams form standing waves on the surface of the photoresist. After development, the photoresist cannot form a steep sidewall structure in the vertical direction.

[0005] In particular, for fabricating aperture-type photonic crystals using holographic exposure technology, obtaining the required periodic grid pattern on the photoresist through development after exposure is also a problem. A single exposure using a holographic exposure system can form a grating pattern on the photoresist. A second exposure by rotating the substrate superimposes the two grating patterns to form a periodic grid pattern. While there are techniques for obtaining masks for fabricating columnar photonic crystals through development, a technique for obtaining the photoresist mask required for fabricating aperture-type photonic crystals through development has not yet emerged. Summary of the Invention

[0006] This disclosure provides a GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system, its preparation method, and its application. It solves a series of problems such as inconsistent photoresist pattern thickness and inability to deeply etch the holographic exposure system, and greatly reduces the preparation difficulty and cost.

[0007] In a first aspect, this disclosure provides a GaAs / GaN-based two-dimensional aperture photonic crystal material based on a holographic exposure system. The material is prepared by using a double exposure method of the holographic exposure system to prepare a photonic crystal grid pattern on a photoresist, transferring the photonic crystal grid pattern using a dry etching composite mask, and obtaining the two-dimensional aperture photonic crystal material by dry etching based on the hard mask pattern.

[0008] Secondly, this disclosure provides a method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system, comprising the following steps:

[0009] (1) A protective layer is deposited on the surface of a GaAs or GaN substrate by vapor deposition, and then a metal Ti thin film layer is deposited on the surface of the protective layer by magnetron sputtering.

[0010] (2) After spin-coating photoresist, perform the first exposure based on the holographic exposure system, rotate the angle of the GaAs or GaN substrate, and perform the second exposure based on the holographic exposure system;

[0011] (3) Different areas have different exposure times. A developer solution diluted according to the ratio is used for development. By strictly controlling the development time, a periodic grid pattern is formed on the photoresist.

[0012] (4) Dry etching is performed on the GaAs or GaN substrate after the treatment in steps (1)-(3) to form a metal Ti mask layer with a periodic grid pattern of photonic crystal on the surface of the GaAs or GaN substrate.

[0013] (5) Remove the photoresist residue from the GaAs or GaN substrate after the treatment of steps (1)-(4), perform dry etching on the protective layer on the surface of the GaAs or GaN substrate, and form a composite mask layer with a periodic grid pattern of photonic crystal on the surface of the GaAs or GaN substrate.

[0014] (6) Dry etching is performed on the GaAs or GaN substrate after the treatment in steps (1)-(5) to obtain a two-dimensional porous photonic crystal material.

[0015] Preferably, in step (1), the material of the protective layer includes SiO2 and SiN. X .

[0016] Preferably, in step (3), the gas used in the dry etching process includes one or more of Cl2, ClB3, and Ar.

[0017] Preferably, in step (3), the developing solution used in the developing process is diluted with deionized water at a ratio of 0.4-0.6, and the developing time is strictly controlled.

[0018] Preferably, in step (4), the gas used in the dry etching process includes one or more of SF6 and CH4 mixed gases.

[0019] Preferably, in step (5), the gas used in the dry etching process includes one or more of Cl2, ClB3, and Ar.

[0020] Secondly, this disclosure provides an application of a GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system, wherein the GaAs / GaN-based two-dimensional porous photonic crystal material is applied in photonic crystal materials.

[0021] In summary, this application has the following beneficial effects:

[0022] 1. In the case of the periodic grid-shaped photoresist mask required for fabricating the aperture photonic crystal in this application, during the development process, while the developing solution completely removes the photoresist in the region with an exposure time of 2Xs, ​​it also carries away a portion of the photoresist in the region with an exposure time of Xs. Therefore, the thickness of the final photoresist mask layer in the vertical direction is not completely uniform. This results in the photoresist grid pattern acting as a mask for varying durations after exposure and development, leading to inconsistent structural depths obtained by dry etching using only photoresist as a mask. At the same time, the photoresist used for holographic lithography is relatively thin and cannot act as a mask for a long time during particle bombardment in the dry etching process, thus preventing the etching of deeper structures.

[0023] 2. In this application, to achieve a good masking effect and increase etching depth, metal or SiO2 is typically used as a hard mask to replace photoresist. Deep etching with SiO2 requires a relatively thick SiO2 mask, but a thick SiO2 mask cannot form steep sidewalls in dry etching processes due to inconsistent photoresist thickness. Conventional metals such as Ni and Au, as hard masks, only require a thinner thickness to achieve good etching resistance. In pattern transfer processes, inconsistent photoresist thickness does not cause problems, but it is difficult to use dry etching for pattern transfer. Ti, as a hard mask, can be used for pattern transfer using dry etching, effectively fabricating hole structures with steep sidewalls. However, the etching gas from Ti further etches the GaAs substrate. Both methods produce extremely non-uniform hole-shaped photonic crystal structures, and photonic crystals have extremely precise requirements for structural parameters, which greatly limits their application.

[0024] 3. This application obtains a periodic grid photoresist mask pattern by strictly controlling the development time after two exposures using a holographic exposure system, and then uses a composite mask for pattern transfer. The photoresist acts as a mask for the metal thin film layer. Dry etching of a thin metal thin film layer, through shallow etching in a short time, allows the photoresist to function as a mask, eliminating the influence of inconsistent thickness in the periodic grid pattern of the photoresist.

[0025] 4. In this application, the metal Ti layer is used as a mask for the protective layer. Due to the different etching gases, even a relatively thin metal can play a good masking role. The protective layer is then patterned again by dry etching. Finally, the protective layer is used as a mask for the substrate. The periodic grid pattern of the mask is used to prepare a hole-type photonic crystal material with a high aspect ratio and steep sidewalls by dry etching. This solves a series of problems such as the inconsistent thickness of the photoresist pattern obtained by the holographic exposure system and the inability to deeply etch the photoresist, and greatly reduces the preparation difficulty and preparation cost.

[0026] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit the scope of protection of this disclosure. Attached Figure Description

[0027] 1. Figure 1 This is a schematic diagram illustrating the principle of forming a periodic grid pattern through two exposures using a holographic exposure system, as described in this application.

[0028] 2. Figure 2 This is an electron microscope image of the periodic grid photoresist mask obtained by double exposure and development using a holographic exposure system, as described in this application.

[0029] 3. Figure 3 This is a schematic diagram of the etching process of GaAs-based two-dimensional aperture photonic crystal material based on a holographic exposure system, as described in this application.

[0030] 4. Figure 4 This is a flowchart of the method for preparing GaAs-based two-dimensional porous photonic crystal materials according to this application;

[0031] 5. Figure 5 This is a top-view electron microscope image of the two-dimensional aperture photonic crystal obtained by three etching processes in this application;

[0032] 6. Figure 6 This is a 45° side view electron microscope image of the two-dimensional aperture photonic crystal obtained by three etching processes in this application;

[0033] 7. Figure 7 This is an electron microscope image of a cross-section of a two-dimensional aperture photonic crystal obtained through three etching processes in this application;

[0034] 8. Figure 8 This is a top-view electron microscope image of a two-dimensional aperture photonic crystal obtained by rotating it 60° and etching it three times during the second exposure of Embodiment 2 of this application;

[0035] 9. Figure 9 This is a top-view electron microscope image of the two-dimensional aperture photonic crystal obtained by three etching processes in Comparative Example 1 of this application. Detailed Implementation

[0036] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0037] Example

[0038] Example 1

[0039] A method for preparing GaAs-based two-dimensional aperture photonic crystal material based on a holographic exposure system is characterized by comprising: performing two exposures using a holographic exposure system, preparing a periodic grid pattern on a photoresist by controlling the concentration of the developer and the development time, transferring the pattern by dry etching a composite mask, and preparing the two-dimensional aperture photonic crystal material by dry etching based on the hard mask pattern.

[0040] 1) A protective layer is deposited on the substrate surface by vapor deposition. The thickness of the thin film layer can be selected according to specific process requirements.

[0041] 2) A thin metal Ti film layer is sputtered and deposited on the surface of the protective layer using magnetron sputtering technology. The thickness of the film layer can be selected according to specific process requirements.

[0042] 3) Spin-coat photoresist onto the substrate surface and perform the first exposure operation on the substrate based on the holographic exposure system.

[0043] 4) Rotate the substrate angle and perform a second exposure operation on the substrate based on the holographic exposure system.

[0044] 5) Control the concentration of the developer and the development time to perform a development process on the substrate, forming a periodic grid pattern on the photoresist to form a photoresist mask layer.

[0045] 6) Perform a dry etching process on the substrate obtained in 5) to form a metal Ti mask layer with a periodic grid pattern on the substrate surface.

[0046] 7) The substrate obtained in 6) is subjected to a photoresist removal process to remove the residual photoresist on the surface. The protective layer on the surface of the substrate is then etched using a dry etching process to form a composite mask layer with a periodic grid pattern on the surface of the substrate.

[0047] 8) The substrate obtained in 7) is subjected to dry etching to obtain a two-dimensional aperture photonic crystal material.

[0048] Electron micrograph of the substrate after holographic double exposure development is shown below. Figure 2 As shown, a grating is prepared by single exposure, while double exposure results in different reactions of the photoresist to the developer due to the different exposure intensities in different areas, forming a periodic grid structure. Figure 3 This is a cross-sectional view of the substrate after the second etching process without photoresist removal. The structure consists of a photoresist mask, a metal mask pattern, a protective layer, and the substrate. Pattern transfer is achieved by dry etching the composite mask, which avoids problems such as uneven etching depth caused by uneven photoresist mask thickness. At the same time, the mask provides conditions for fabricating two-dimensional aperture photonic crystal materials with steep sidewalls and high aspect ratio in subsequent processes.

[0049] The flowchart of the fabrication process of the two-dimensional aperture photonic crystal based on the holographic exposure system of this invention is as follows: Figure 3As shown, specifically, a 150nm thick SiO2 protective layer is first deposited on the cleaned GaAs substrate using magnetron sputtering, followed by the evaporation of a 100nm thick metallic Ti layer. Then, a positive resist diluted with a positive resist diluent is uniformly spin-coated (because the light source energy of the holographic exposure system is relatively weak, a conventional thickness of positive resist cannot expose a precise pattern, so a photoresist is used: the positive resist diluent is a 10:8 photoresist). After that, the substrate is exposed for 180 seconds using a holographic exposure system with a light source of 325nm, rotated 90°, and exposed again for 180 seconds. After exposure, a diluted developer (developer:deionized water = 5:2) is used for development for 5 seconds, forming a periodic grid pattern on the photoresist. The film is then hardened by heating at 120°C for 120 seconds. Subsequently, pattern transfer is achieved by anisotropic etching of the metal thin film in ICP (a mixed gas of Cl2, ClB3, and Ar2 is used in this example). After cleaning the substrate, residual photoresist is removed by a coating machine. Then, SiO2 is etched again by ICP for pattern transfer (a mixed gas of SF6 and CH4 is used in this example). Finally, a dry etching process is used to etch a columnar two-dimensional photonic crystal with a high aspect ratio, steep sidewalls, and uniform structure (a mixed gas of Cl2, ClB3, and Ar2 is used in this example).

[0050] The two-dimensional photonic crystal material obtained in Example 1 was used for experimental testing, and the results are as follows:

[0051] like Figure 5 As shown, the etched pattern is uniform and clear, the cycle is stable, and the finished product area is large.

[0052] like Figure 6 As shown, the 45° side view of the material reveals a good surface structure and a very round pore shape.

[0053] like Figure 7 The image shows a cross-section after etching, revealing a deep and uniform etching depth.

[0054] Example 2

[0055] The two-dimensional aperture photonic crystal of the holographic exposure system prepared according to the method of Example 1 was processed. The difference was that only the top view was examined using an electron microscope; other conditions remained unchanged. Previously, the second exposure involved a 90° rotation, but in this example, it was only rotated by 60°, thus altering the lattice shape. Figure 8 As shown, the square lattice was changed to a rhombic lattice.

[0056] Comparative Example

[0057] Comparative Example 1

[0058] The two-dimensional aperture photonic crystal of the holographic exposure system prepared according to the method of Example 1 was processed, except that only one layer of photoresist was used as a mask on the substrate, while other conditions were the same.

[0059] like Figure 9 As shown, due to the uneven thickness of the photoresist mask obtained after development, different locations can withstand different etching times. After the same etching time, some locations of the photoresist have been completely etched away, failing to function as a mask and thus preventing the formation of a large-area, uniform aperture photonic crystal.

[0060] The above description is merely an exemplary embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system, characterized in that, Includes the following steps: (1) A protective layer is deposited on the surface of a GaAs or GaN substrate by vapor deposition, and then a metal Ti thin film layer is deposited on the surface of the protective layer by magnetron sputtering. (2) After spin-coating photoresist, perform the first exposure based on the holographic exposure system, rotate the angle of the GaAs or GaN substrate, and perform the second exposure based on the holographic exposure system; (3) Different areas have different exposure times. A developer solution diluted according to the ratio is used for development. By strictly controlling the development time, a periodic grid pattern is formed on the photoresist. (4) Dry etching is performed on the GaAs or GaN substrate after the treatment in steps (1)-(3) to form a metal Ti mask layer with a periodic grid pattern of photonic crystal on the surface of the GaAs or GaN substrate. (5) Remove the photoresist residue from the GaAs or GaN substrate after the treatment of steps (1)-(4), perform dry etching on the protective layer on the surface of the GaAs or GaN substrate, and form a composite mask layer with a periodic grid pattern of photonic crystal on the surface of the GaAs or GaN substrate. (6) Dry etching is performed on the GaAs or GaN substrate after the treatment in steps (1)-(5) to obtain a two-dimensional porous photonic crystal material.

2. The method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system according to claim 1, characterized in that, In step (1), the material of the protective layer includes SiO2 and SiN. X .

3. The method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system according to claim 1, characterized in that, In step (4), the gas used in the dry etching process includes one or more of Cl2, ClB3, and Ar2 mixed gases.

4. The method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system according to claim 1, characterized in that, In step (3), the developing solution used in the developing process is diluted with deionized water at a ratio of 0.4-0.6, and the developing time is strictly controlled.

5. The method for preparing GaAs / GaN-based two-dimensional porous photonic crystal materials based on a holographic exposure system according to claim 1, characterized in that, In step (5), the gas used in the dry etching process includes one or more of SF6 and CH4 mixed gases.

6. The method for preparing GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system according to claim 1, characterized in that, In step (6), the gas used in the dry etching process includes one or more of Cl2, ClB3, and Ar mixed gases.

7. A GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system, wherein the material is prepared by the preparation method of GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system as described in any one of claims 1 to 6, characterized in that, The material is prepared by using a holographic exposure system with a double exposure method to create a photonic crystal grid pattern on a photoresist, and then using a dry etching composite mask to transfer the photonic crystal grid pattern. The two-dimensional aperture photonic crystal material is obtained by dry etching based on the hard mask pattern.

8. The application of the GaAs / GaN-based two-dimensional porous photonic crystal material based on a holographic exposure system according to claim 7, characterized in that, The GaAs / GaN-based two-dimensional porous photonic crystal material is used in photonic crystal materials.

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