A GaAs / GaN-based two-dimensional photonic crystal material and its preparation method

Abstract

A GaAs / GaN-based two-dimensional photonic crystal material and a preparation method thereof belong to the field of semiconductor optoelectronic technology. The preparation method of the present invention comprises preparing a photonic crystal lattice pattern on a photoresist using a double exposure method of a holographic exposure system, transferring the photonic crystal lattice pattern using a dry etching composite mask, and obtaining a two-dimensional photonic crystal material by dry etching based on a hard mask pattern. Also provided are GaAs / GaN-based two-dimensional photonic crystal materials obtained by the preparation method and their applications. Using the preparation method of the present invention, a two-dimensional photonic crystal structure with a high aspect ratio, steeper sidewalls, and good periodic morphology can be obtained on the substrate surface, avoiding the disadvantage of a sinusoidal morphology caused by the standing wave effect of the holographic exposure system, and having a positive effect on improving the performance of two-dimensional photonic crystals and their use for large-scale preparation.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor optoelectronic technology, and in particular relates to a GaAs / GaN-based two-dimensional photonic crystal material based on a holographic exposure system, a preparation method thereof, and an application thereof. Background Art

[0002] Photonic crystals possess the characteristic of a photonic bandgap, exhibiting dielectric constants within the passband frequency domain that are unattainable by existing homogeneous media. By introducing defect modes within the completely bandgap or mode-gap frequency domain, light can be guided to propagate at a 90-degree angle, effectively controlling electromagnetic wave propagation. Therefore, photonic crystal materials possess the characteristics of a "photonic bandgap" and "photon localization." Their unique properties and potential for numerous applications have sparked significant interest in the theoretical analysis and experimental research of photonic crystal materials. Two-dimensional photonic crystal materials hold great promise for application in optical communications and are attracting significant attention from scholars worldwide.

[0003] Due to the high dimensional precision required, traditional methods for fabricating photonic crystal materials often rely on electron beam lithography and nanoimprinting, which are very expensive and unfavorable for the preparation of large-area semiconductor nanostructure arrays and large-scale industrialization. However, the holographic exposure system, with its unique maskless exposure mechanism, greatly reduces production costs, making it possible to fabricate structure arrays on a large scale.

[0004] When exposing photonic crystal lattice patterns in holographic exposure systems, the system's structure often creates standing waves on the substrate surface, preventing the photoresist from forming steep sidewalls in the vertical direction, significantly increasing the process's complexity. Due to the standing wave effect, the thickness of the photoresist pattern perpendicular to the substrate is uneven in the traditional photoresist mask process. The photoresist lattice pattern acts as a mask for varying periods of time, resulting in varying depths during dry etching. Furthermore, due to the thin thickness of the photoresist, it cannot function as a mask for extended periods during particle bombardment during the dry etching process, preventing the formation of photonic crystals with high aspect ratios. To achieve a good masking effect and increase etching depth, a metal or SiO2 hard mask is typically used instead of the photoresist to act as a mask. First, deep etching requires the SiO2 mask to have a certain thickness, but thicker SiO2 cannot form steep sidewalls during dry etching due to the uneven thickness of the photoresist. Conventional metals such as Ni and Au only need a relatively thin thickness as a hard mask to achieve good etching resistance. At the same time, the uneven thickness of the photoresist will not cause any impact during the pattern transfer process. However, it is difficult to use dry etching for pattern transfer. Due to the side etching caused by wet corrosion, the transferred mask pattern is very easy to deform, resulting in extremely uneven photonic crystal lattice structure. Photonic crystals have extremely precise requirements for structural parameters, which greatly increases the difficulty of the manufacturing process. Metal Ti can be used as a hard mask for pattern transfer using dry etching, which can effectively produce a lattice structure with steep side walls. However, the etching gas of Ti will further etch the GaAs substrate, which undoubtedly increases the difficulty of the process. Summary of the Invention

[0005] In view of the defects existing in the above-mentioned prior art, the purpose of the present invention is to design and provide a GaAs / GaN-based two-dimensional photonic crystal material based on a holographic exposure system, and its preparation method and application.

[0006] The present invention prepares a photonic crystal lattice pattern through double exposure using a holographic exposure system, and uses a composite mask for pattern transfer. Photoresist is used as a mask for the metal film layer, and a thinner metal film layer is dry-etched. Through shallow etching for a relatively short time, the photoresist acts as a mask, eliminating the effects of uneven thickness of the photoresist lattice pattern. Furthermore, the metal Ti layer is used as a mask for the protective layer. Due to different etching gases, even thinner metals can have a good masking effect. The protective layer is dry-etched to transfer the pattern again. Finally, the protective layer is used as a mask for the substrate, and the photonic crystal lattice pattern of the mask is used to prepare a photonic crystal material with a high aspect ratio and steep sidewalls through dry etching. This solves a series of problems such as uneven thickness of the lattice pattern of the holographic exposure system and the inability to perform deep etching, greatly reducing the difficulty and cost of preparation.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing GaAs / GaN-based two-dimensional photonic crystal materials based on a holographic exposure system is characterized by comprising preparing a photonic crystal lattice pattern on a photoresist using a double exposure method of a holographic exposure system, transferring the photonic crystal lattice pattern using a dry etching composite mask, and obtaining the two-dimensional photonic crystal material by dry etching based on a hard mask pattern.

[0009] The method for preparing GaAs / GaN-based two-dimensional photonic crystal materials based on a holographic exposure system is characterized by comprising the following steps:

[0010] (1) Evaporate a protective layer on the surface of the GaAs or GaN substrate (the evaporated protective layer can be SiO2, SiN X and the like silicon compound material), and then sputtering and evaporating a metal Ti thin film layer on the surface of the protective layer by a magnetron sputtering method;

[0011] (2) After spin coating the photoresist, the first exposure is performed based on the holographic exposure system, the angle of the GaAs or GaN substrate is rotated, and the second exposure is performed based on the holographic exposure system, and a development method is performed to form a photonic crystal lattice pattern on the photoresist; the period of the photonic crystal period can be changed by the holographic exposure system, and its period is specifically related to the laser source wavelength and the system optical path of the holographic exposure system.

[0012] (3) dry etching the GaAs or GaN substrate processed in steps (1) to (2) above to form a metal Ti mask layer having a photonic crystal lattice pattern on the surface of the GaAs or GaN substrate;

[0013] (4) The GaAs or GaN substrate treated in the above steps (1) to (3) is subjected to a debonding treatment to remove the residual photoresist on the surface, and the protective layer on the surface of the GaAs or GaN substrate is dry-etched to form a composite mask layer with a photonic crystal lattice pattern on the surface of the GaAs or GaN substrate; since the gas used to dry-etch the protective layer will also etch the GaAs or GaN substrate, the protective layer here plays a role in protecting the GaAs or GaN substrate, and at the same time, when dry-etching the GaAs or GaN substrate, the protective layer will also act as an etching mask. The ratio of the dry-etching gas or mixed gas, the flow rate of each gas, and the etching time will all affect the etching depth of the photonic crystal. Multiple parameters need to be coordinated to obtain a photonic crystal with good sidewall morphology and a deep etching depth. For example, the flow rate of each gas, the ratio of the mixed gas, and the ICP power and RF power will all affect the etching sidewall morphology and etching rate.

[0014] (5) Dry etching the GaAs or GaN substrate processed in the above steps (1) to (4) to obtain a two-dimensional photonic crystal material.

[0015] The preparation method is characterized in that the material of the protective layer in step (1) includes SiO2, SiN X .

[0016] In the step (2), the light source for the first exposure is 325 nm and the exposure time is 200 seconds; the laser source wavelength for the second exposure is 325 nm and the exposure time is 200 seconds;

[0017] The two beams of light that interfere with each other in the holographic exposure system have equal incident angles on the substrate, and the angle range is 0° to 90°.

[0018] The preparation method is characterized in that the gas used in the dry etching process in step (3) includes a mixed gas of one or more of Cl2, ClB3, and Ar.

[0019] The preparation method is characterized in that the gas used in the dry etching process in step (4) includes a mixed gas of one or more of SF6 and CH4.

[0020] The preparation method is characterized in that the gas used in the dry etching process in step (5) includes a mixed gas of one or more of Cl2, ClB3, and Ar.

[0021] A GaAs / GaN-based two-dimensional photonic crystal material based on a holographic exposure system, characterized in that it is prepared by any of the above-mentioned preparation methods.

[0022] The GaAs / GaN-based two-dimensional photonic crystal material based on the holographic exposure system is characterized in that the GaAs / GaN-based two-dimensional photonic crystal material has a high aspect ratio and steep side walls.

[0023] The GaAs / GaN-based two-dimensional photonic crystal material is used as a photonic crystal material.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a GaAs / GaN-based two-dimensional photonic crystal preparation method based on a holographic exposure system, which can avoid the high production cost disadvantage of traditional methods, use a composite mask to realize the pattern transfer of photoresist, avoid the influence of the exposure stage process on the morphology of the two-dimensional photonic crystal, and solve the contradiction between the holographic exposure system and the preparation of two-dimensional photonic crystal materials.

[0026] In the GaAs / GaN-based two-dimensional photonic crystal preparation method of the present invention, a pattern is produced by double exposure using a holographic exposure system and three dry etchings are performed to prepare the two-dimensional photonic crystal material. The wavelength can be selected by changing structural parameters such as the photonic crystal period (the period of the photonic crystal can be changed by the holographic exposure system, and the period specifically requires the cooperation of two parameters, the laser source wavelength of the holographic exposure system and the system optical path, to obtain the desired period) and the etching depth, thereby improving the application potential in the field of semiconductor lasers. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a top-view electron microscope image of the periodic structure prepared by double exposure based on the holographic exposure system in Example 1;

[0028] Figure 2 Schematic cross-sectional view of the etching process of GaAs-based two-dimensional photonic crystal material based on the holographic exposure system in Example 1;

[0029] Figure 3 This is a flow chart of the preparation method of GaAs-based two-dimensional photonic crystal materials;

[0030] Figure 4 This is a top-view electron microscope image of the two-dimensional photonic crystal material obtained in Example 1;

[0031] Figure 5 This is a 45° side-view electron microscope image of the two-dimensional photonic crystal material obtained in Example 1;

[0032] Figure 6 This is an electron microscope image of the cross section of the two-dimensional photonic crystal material obtained in Example 1. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Example 1:

[0035] A method for preparing GaAs-based two-dimensional photonic crystal materials based on a holographic exposure system is characterized in that it includes: preparing a photonic crystal lattice pattern on a photoresist using a double exposure method of the holographic exposure system, dry etching a composite mask to transfer the pattern, and dry etching based on a hard mask pattern to prepare the two-dimensional photonic crystal material.

[0036] 1) First, a 150 nm thick SiO2 protective layer is deposited on the cleaned GaAs substrate by magnetron sputtering. The thickness of the film layer can be selected according to the specific process requirements.

[0037] 2) A 100 nm thick metal Ti thin film layer is sputter-deposited on the surface of the protective layer by magnetron sputtering technology. The thickness of the thin film layer can be selected according to specific process requirements.

[0038] 3) A positive photoresist diluted with a positive photoresist diluent is evenly spin-coated on the substrate surface. (Due to the weak light source energy of the holographic exposure system, conventional thickness positive photoresists cannot expose precise patterns. Therefore, a photoresist with a photoresist:positive photoresist diluent ratio of 10:8 is used.) The substrate is then exposed for the first time using the holographic exposure system, i.e., the substrate is exposed for 200 seconds using a 325 nm light source.

[0039] 4) Rotate the substrate by 90°, expose the substrate for a second time for 200 seconds using a holographic exposure system, and develop with a developer to form a photonic crystal lattice pattern on the photoresist.

[0040] 5) The substrate obtained in 4) was subjected to a dry etching process to form a metal Ti mask layer with a dot pattern on the substrate surface. Specifically, the film was hardened by heating on a hot plate at 120°C for 120 seconds. The pattern was then transferred by anisotropic etching of the metal film in an ICP process (using a mixture of Cl2, ClB3, and Ar2).

[0041] 6) The substrate obtained in 5) is subjected to a debonding treatment to remove any residual photoresist from the surface. The protective layer on the substrate surface is then etched by dry etching to form a composite mask layer having a dot pattern on the substrate surface. Specifically, the SiO2 is etched by ICP etching (using a mixture of SF6 and CH4) and the pattern is transferred again.

[0042] 7) The substrate obtained in 6) is again subjected to a dry etching process (using a mixed gas of Cl2, ClB3, and Ar2) to etch out a two-dimensional photonic crystal material with a high aspect ratio, steep sidewalls, and uniform structure.

[0043] The electron microscope image of the substrate after holographic exposure and double exposure is as follows: Figure 1 As shown, a single exposure is used to prepare a grating, and a double exposure is used to prepare a grating. Since the photoresist in different areas is exposed to different intensities, it reacts differently to the developer, forming a periodic structure of a lattice. Figure 2 This is a schematic cross-section of a substrate after the first etch, but before the resist is removed. The structure consists of a photoresist mask, a metal mask pattern, a protective layer, and the substrate. Pattern transfer via dry etching with a composite mask avoids uneven etching depths caused by uneven photoresist mask thickness. Furthermore, the mask facilitates the fabrication of two-dimensional photonic crystals with steep sidewalls and high aspect ratios in subsequent processes.

[0044] The process flow chart of the two-dimensional photonic crystal production based on the holographic exposure system of the present invention is as follows: Figure 3 shown.

[0045] Material property testing:

[0046] The two-dimensional photonic crystal material obtained in Example 1 was tested and the results were as follows:

[0047] like Figure 4 As shown, it can be seen that the etched pattern is uniform and clear, and the period is stable.

[0048] like Figure 5 As shown, it can be seen from the 45° side view of the material that the surface structure is evenly distributed and the finished product area is large.

[0049] like Figure 6 This is a cross-sectional view after etching. It can be seen that the etching depth is deep and uniform.

[0050] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims of the present invention.

Claims

1. A method for preparing GaAs / GaN-based two-dimensional photonic crystal materials based on a holographic exposure system, characterized in that The method comprises preparing a photonic crystal lattice pattern on a photoresist by a double exposure method using a holographic exposure system, transferring the photonic crystal lattice pattern by using a dry etching composite mask, and obtaining a two-dimensional photonic crystal material by dry etching based on a hard mask pattern; The composite mask includes a protective layer as a mask for a substrate, a metal film layer as a mask for the protective layer, and a photoresist as a mask for the metal film layer.

2. The method for preparing GaAs / GaN-based two-dimensional photonic crystal materials based on a holographic exposure system according to claim 1, characterized in that Specifically include: Step 1: depositing a protective layer on the surface of a GaAs or GaN substrate, and then sputtering and depositing a metal Ti thin film layer on the surface of the protective layer by a magnetron sputtering method; Step 2: After spin coating the photoresist, perform a first exposure using a holographic exposure system, rotate the angle of the GaAs or GaN substrate, perform a second exposure using the holographic exposure system, and perform a development method to form a photonic crystal lattice pattern on the photoresist; Step 3, dry etching the GaAs or GaN substrate processed in Steps 1 and 2 above to form a metal Ti mask layer having a photonic crystal lattice pattern on the surface of the GaAs or GaN substrate; Step 4: performing a desizing process on the GaAs or GaN substrate processed in Steps 1 to 3 to remove the residual photoresist on the surface, dry-etching the protective layer on the surface of the GaAs or GaN substrate, and forming a composite mask layer having a photonic crystal lattice pattern on the surface of the GaAs or GaN substrate; Step 5: dry-etching the GaAs or GaN substrate processed in steps 1 to 4 to obtain a two-dimensional photonic crystal material.

3. The preparation method according to claim 2, wherein The material of the protective layer in step 1 includes SiO2, SiN X ; In step 2, the light source for the first exposure is 325 nm and the time is 200 seconds; the laser source wavelength for the second exposure is 325 nm and the time is 200 seconds; The two beams of light that interfere with each other in the holographic exposure system have equal incident angles on the substrate, and the angle range is 0° to 90°.

4. The preparation method according to claim 2, wherein The gas used in the dry etching process in step 3 includes a mixed gas of one or more of Cl2, ClB3, and Ar.

5. The preparation method according to claim 2, wherein The gas used in the dry etching process in step 4 includes a mixed gas of one or more of SF6 and CH4.

6. The preparation method according to claim 2, wherein The gas used in the dry etching process in step 5 includes a mixed gas of one or more of Cl2, ClB3, and Ar.

7. A GaAs / GaN-based two-dimensional photonic crystal material based on a holographic exposure system, characterized in that It is prepared by the preparation method according to any one of claims 1 to 6.

8. The GaAs / GaN-based two-dimensional photonic crystal material based on the holographic exposure system according to claim 7, characterized in that The GaAs / GaN-based two-dimensional photonic crystal material has a high aspect ratio and steep side walls.

9. Use of the GaAs / GaN-based two-dimensional photonic crystal material as claimed in claim 7 as a photonic crystal material.

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