CN101726769A - Long laminated sub-wave reflection-reducing structure and preparation method thereof - Google Patents

Abstract

The present invention discloses a laminated sub-wavelength anti-reflection structure, including a sub-wavelength pattern formed by etching on the surface of a high-refractive index material that requires anti-reflection, and a dielectric layer deposited and grown on the surface of the aforementioned sub-wavelength pattern. Together constitute the laminated sub-wavelength structure, and its structural pattern is calculated according to the refractive index distribution of the materials used and the wavelength and angle range of the incident light to be anti-reflection. The sub-wavelength anti-reflection structure of the present invention is applied to active optoelectronic devices on the surface of high refractive index, and can truly and effectively realize the wide-spectrum wide-angle transmission effect. Compared with the prior art, the present invention can effectively passivate the sub-wavelength anti-reflection structure, reduce non-radiative recombination centers, suppress non-radiative recombination loss, and effectively increase the performance of corresponding optoelectronic devices; and, in view of the refraction of air, dielectric materials and substrate materials The rate changes sequentially, so the use of a laminated sub-wavelength anti-reflection structure can also reduce the difficulty of preparation, or obtain better anti-reflection performance under the same preparation conditions.

Description

Laminated sub-wavelength anti-reflection structure and preparation method thereof

technical field

The invention relates to a nanostructure, in particular to a sub-wavelength anti-reflection structure suitable for solar cell systems, light display surface emitting devices, etc. that require wide-spectrum and wide-angle light in and out, and a preparation method thereof, belonging to the field of micro-nano photonics.

Background technique

The interface reflectivity between substances with different refractive index is an important parameter that affects the performance of receiving light, emitting light, and transmitting optical devices and equipment. Extremely low interface reflectivity is the pursuit of light display, broadband light source, solar cells, lenses and other fields. Important indicators. Usually, vapor-deposited optical anti-reflection film is used to reduce optical interface reflection. In order to reduce the interface reflectance as far as possible in a wide-angle and wide-spectrum range, it is usually necessary to design an optical film with multiple layers of vapor deposition, and the optical film material is not unique. The complex film structure not only increases the process requirements of the coating itself, but also reduces the success rate; it is also inevitably subjected to temperature, humidity changes and even mechanical shocks during use. The difference in thermal expansion coefficient, humidity coefficient and elastic modulus between different materials will inevitably cause changes in the refractive index and thickness of the film layer material, and even cause part of the optical film to fall off badly. Any kind of change will lead to coherence-based The decrease or even complete destruction of the optical film transmittance of the principle will greatly affect the performance of the corresponding devices and equipment.

The subwavelength grating structure is a surface relief grating structure whose period is smaller than the wavelength of the incident light (as shown in Figure 1a and Figure 1b). The refractive indices of the two media and the corresponding subwavelength grating structure are n ₁ , n ₂ , and n ₃ , respectively. The period is Λ, the grating vector $G=\frac{2\mathrm{\π}}{\mathrm{\Λ}},$ The incident angle of the incident light and the wave vector of the light wave in vacuum are θ ₁ and k respectively, and the conditions for the occurrence of zero-order diffraction can be expressed as follows:

|n ₁ ksinθ ₁ +mG|＞n _i k, i=1, 2, 3and m=±1,±2,±3,...(1),

It can be seen from this formula that the conditions for zero-order diffraction of incident light of a specific wavelength depend not only on the incident angle of the incident light, but also on the refractive index of the material and the period of the grating. When the period of the grating is small enough, the vector value of the grating is large enough, so that the above inequality no longer depends on the wave vector of the incident light and the size of the incident angle, that is, the zero-order diffraction can be obtained in a wide spectrum and a large angle range, A very high anti-reflection effect can be obtained, and it becomes an extremely effective way to reduce the interface reflectivity in a wide-angle and wide-spectrum range.

However, in terms of production, there are still limitations in using sub-wavelength structures to achieve anti-reflection effects in a wide-angle and wide-spectrum range. On the one hand, if the method of interface material etching is directly used, according to the principle of subwavelength zero-order diffraction, it is undoubtedly possible to obtain extremely low reflectivity in a wide-angle and wide-spectrum range, but the etched surface will produce many defects, especially for nanometer structure, the specific surface area increases, and the non-radiative recombination brought about by surface defects. The existence of these non-radiative recombination centers will cause great losses to the optoelectronic devices, especially active optoelectronic devices. Optical interface, the fatal factor to improve the performance of corresponding devices. Another subwavelength structure is to grow subwavelength nanostructures with graded refractive index on the surface of the original material. This method will undoubtedly not cause non-radiative recombination of the surface and bring additional photoelectric loss. However, for substrate materials with a high refractive index (such as Si, GaAs, InP and other semiconductor materials), it is almost impossible to find a dielectric film material with a matching refractive index. Therefore, the interface between the high refractive index material and the dielectric material is undoubtedly still There is a large reflection loss, which becomes a physical limitation to achieve extremely low reflectivity with this method.

Contents of the invention

The purpose of the present invention is to propose a novel sub-wavelength anti-reflection structure and a preparation method thereof, so as to solve the limitation of the existing sub-wavelength structure in improving the overall performance of the device. While reducing the interface reflection loss in a wide spectrum and a large angle range, it does not increase the non-radiative recombination loss of the surface, and reduces the difficulty of preparing sub-wavelength structures.

The technical solution that realizes first object of the present invention is:

The laminated sub-wavelength anti-reflection structure, whose structural pattern is calculated according to the refractive index distribution of the material used and the wavelength and angle range of the incident light to be anti-reflected, is characterized in that: the laminated sub-wavelength anti-reflection structure includes two parts: One part is the sub-wavelength pattern formed by etching on the surface of the high-refractive index material that needs anti-reflection; the other part is the dielectric layer deposited and grown on the surface of the aforementioned sub-wavelength pattern, and the two are integrated to form a laminated sub-wavelength anti-reflection structure.

Further, the dielectric layer is a uniform single-layer dielectric film, a multi-layer dielectric film, or a dielectric film with a graded refractive index, or a dielectric nanostructure with a graded refractive index, and the material of the dielectric layer depends on the required anti-reflection material to determine the refractive index.

Further, the sub-wavelength pattern is a pattern that can constitute a graded refractive index.

Another object of the present invention will be achieved through the following technical solutions:

A method for preparing a laminated subwavelength antireflection structure, the characteristic steps of which include:

I. Calculate and design the laminated sub-wavelength structure according to the wavelength and angle range of the incident light to be anti-reflection, including the sub-wavelength pattern etched on the high refractive index material for anti-reflection and the sub-wavelength pattern of the dielectric layer formed by deposition;

II. Forming a sub-wavelength structural pattern mask on the required anti-reflection high-refractive index material, and forming a sub-wavelength pattern with a corresponding aspect ratio on the substrate by etching;

III, removing the mask and cleaning the high refractive index substrate material with sub-wavelength patterns;

IV. Growing a dielectric layer on the subwavelength pattern of the substrate, and the material and shape of the dielectric film are calculated according to step I.

Further, in the aforementioned method for preparing a laminated subwavelength antireflection structure, the substrate material in step II has a refractive index n higher than the highest refractive index of the natural medium material, such as the refractive index of TiO _2.6 ; and in step II The method for forming the pattern mask includes electron beam exposure, coherent photolithography and self-assembly, and the etching method includes reactive ion etching, inductively coupled plasma etching, electron cyclotron resonance etching and wet etching.

Further, in the aforementioned method for preparing the subwavelength antireflection structure, the method of covering the dielectric film in step IV includes magnetron sputtering, pulsed laser deposition, thermal evaporation, electron beam evaporation, atomic layer deposition, and plasma chemical vapor phase deposition.

The substantive features and remarkable advantages of the subwavelength antireflection structure and its preparation method of the present invention are mainly reflected in:

The sub-wavelength anti-reflection structure in the form of a laminate is used to replace the original single-layer sub-wavelength structure. Radiation recombination loss makes the sub-wavelength anti-reflection structure truly become the interface of active optoelectronic devices, effectively increasing the performance of corresponding optoelectronic devices; The wavelength antireflection structure can also reduce the difficulty of preparation, or obtain better antireflection performance under the same preparation conditions.

Description of drawings

Figure 1 is a schematic diagram of the first part of the laminated sub-wavelength structure obtained by etching on a material with a high refractive index that requires an anti-reflection effect, wherein Figure 1a is a pyramid-shaped structure, and Figure 1b is a wedge-shaped structure;

Fig. 2 is a laminated subwavelength antireflection structure further prepared by growing dielectric materials on the subwavelength antireflection structure of the optical interface material in the present invention, wherein

Figure 2 is a schematic diagram of a complete laminated subwavelength anti-reflection structure; including: (2a) the first part is etched to form a pyramid, and the second part is to deposit a uniform dielectric film, still forming a pyramid; (2b) the first part is etched to form a wedge structure, the second part uniformly deposits the dielectric film, still forming a wedge-shaped structure; (2c) the first part is etching to form a wedge-shaped structure, the second part uniformly deposits the dielectric film, and finally forms a pyramid-shaped laminated sub-wavelength structure; (2d) the first part For the wedge-shaped structure formed by etching, the second part is to deposit a thicker dielectric film with a graded refractive index to form a pyramid-shaped laminated sub-wavelength anti-reflection structure

Fig. 3 is a schematic diagram of the influence of different refractive index media on the reflectivity performance of the subwavelength anti-reflection structure;

Figure 4a is a schematic diagram of the change in reflectivity of a laminated sub-wavelength structure with a medium refractive index n=1.63 under different incident angles;

Fig. 4b is a schematic diagram of the change of the reflectivity of the laminated sub-wavelength structure with the medium refractive index n=1 under different incident angles.

Detailed ways

In order to break through the limitations of the existing subwavelength structure in improving the overall performance of the device, the present invention discloses a laminated subwavelength antireflection structure. The shape of the subwavelength antireflection structure is calculated according to the wavelength and angle range of the incident light to be antireflection Obtained, characterized in that: the laminated sub-wavelength anti-reflection structure includes two parts: the first part is to form a sub-wavelength pattern by etching on the surface of the high refractive index material that needs anti-reflection; the second part is the sub-wavelength pattern in the first part The dielectric layer grown on the surface is re-deposited, and the two are integrated to form a laminated sub-wavelength anti-reflection structure.

The sub-wavelength anti-reflection structure can be prepared through the following technical solutions:

Firstly, select the substrate material that needs sub-wavelength anti-reflection structure. This material refers to the interface material that needs a wide spectrum and wide angle range of incident light, especially the interface material whose refractive index is higher than that of ordinary natural media (n≥2.6).

Then calculate and design the corresponding sub-wavelength structure according to the wavelength and angle range of the incident light to be anti-reflection, including the sub-wavelength anti-reflection structure etched on the substrate and the sub-wavelength anti-reflection dielectric layer to be grown;

Then adopt an appropriate method to form a subwavelength structure pattern mask on the substrate material, and form a subwavelength structure with a certain aspect ratio on the original substrate by etching under the pattern mask;

Then, etch the substrate material with sub-wavelength structure on the surface after etching to remove the mask material on the substrate, and clean the substrate with water or organic solvent;

Finally, a corresponding sub-wavelength structure dielectric layer is prepared on the sub-wavelength structure pattern substrate by deposition or other methods, and the sub-wavelength anti-reflection structure of the laminated structure is completed.

The options for each step of the above preparation method and points to be noted include:

1. The refractive index of the selected dielectric film is between the substrate material and air. Figure 3 shows the reflection of the laminated sub-wavelength anti-reflection structure with the same geometric structure but different refractive index media simulated by the rigorous coupled wave analysis method Schematic diagram of the impact on rate performance. It can be seen that for optical interface materials with high refractive index, increasing the refractive index of the dielectric layer can effectively reduce the interface reflectance in a wide spectral range. Especially for the high refractive index region with steep dispersion relation, the effect is more obvious.

2. When designing subwavelength structures, it is also necessary to consider comprehensive factors such as high refractive index materials, dielectric film materials to be deposited, and air;

3. The formation of the sub-wavelength structure mask can be realized by electron beam exposure, coherent lithography or various self-assembly methods;

4. In the etching method described therein, whether it is to form a sub-wavelength structure on the substrate or remove the mask, depending on the mask material, conventional techniques such as wet etching or dry etching can be used To achieve this, as long as the mask material can be completely and completely removed after the sub-wavelength structure is formed on the high-refractive index material, the high-refractive index material that does not damage the sub-wavelength structure shall prevail;

5. Regarding the dielectric layer, it can be a dielectric film, or a dielectric nanocolumn or nanotube according to the design requirements, as long as it can passivate the subwavelength nanostructure of the substrate well, and at the same time ensure that its refractive index meets the subwavelength design The refractive index used in the process is sufficient. According to actual needs, its preparation method can be various equipment such as magnetron sputtering, pulsed laser deposition, thermal evaporation, electron beam evaporation, atomic layer deposition, plasma chemical vapor deposition, and other growth preparation methods of nanocolumns and nanotubes.

The stacked sub-wavelength anti-reflection structure shown in Figure 2a to Figure 2b, wherein the stacked sub-wavelength anti-reflection structure shown in Figure 2a includes: a pyramid-shaped sub-wavelength anti-reflection structure formed by etching a high refractive index substrate material and a uniformly deposited dielectric film on the structure; the stacked subwavelength antireflection structure shown in Figure 2b includes: a wedge-shaped subwavelength antireflective structure formed by etching a high refractive index substrate material and a uniformly deposited dielectric film on the structure , still forming a wedge-shaped stacked subwavelength anti-reflection structure; the stacked sub-wavelength anti-reflection structure shown in Figure 2c includes: a wedge-shaped sub-wavelength anti-reflection structure formed by etching a high-refractive index substrate material and a thicker layer deposited on the structure The dielectric film finally forms a pyramid-shaped stacked subwavelength anti-reflection structure; the stacked sub-wavelength anti-reflection structure shown in Figure 2d includes: a wedge-shaped sub-wavelength anti-reflection structure formed by etching a high-refractive index substrate material and deposited Thick graded-index dielectric film finally forms a pyramid-shaped laminated subwavelength anti-reflection structure

It can be seen from the change curves of reflectivity shown in Fig. 4a and Fig. 4b that for subwavelength structures with the same geometric structure, the stacked subwavelength structure with higher refractive index can obtain lower reflectance in wide angle and wide spectrum range. Reflectivity. For Figures 4a and 4b, the geometry of the sub-wavelength anti-reflection structure is a hexagonal close-packed conical shape, wherein the diameter of the cone base is 100nm, the cone arrangement period is 200nm, and the cone height is 500nm. When the dielectric layer is air, it is quite Because it is only a single-layer sub-wavelength anti-reflection structure; its reflectivity curve in wide-angle and wide-spectrum range is as shown in Figure 4b; when the refractive index of the medium layer is n=1.63, its reflection in wide-angle and wide-spectrum range The rate curve is shown in Figure 4a. It can be seen that under the same preparation conditions, the laminated subwavelength anti-reflection structure can indeed reduce the interface reflectance more effectively in a wide-angle and wide-spectrum range.

The sub-wavelength anti-reflection structure and its manufacturing method of the present invention have the advantages of effectively passivating the sub-wavelength anti-reflection structure, reducing non-radiative recombination centers, suppressing non-radiative recombination losses, and effectively increasing the performance of corresponding optoelectronic devices; The refractive index of air, dielectric material, and substrate material changes sequentially, so the use of a laminated subwavelength anti-reflection structure will undoubtedly reduce the difficulty of preparation, or obtain better anti-reflection performance under the same preparation conditions.

Claims (6)

1. The laminated sub-wavelength anti-reflection structure, whose structural pattern is calculated according to the refractive index distribution of the material used and the wavelength and angle range of the incident light to be anti-reflected, is characterized in that: the laminated sub-wavelength anti-reflection structure includes two parts : Part of it is a sub-wavelength pattern formed by etching on the surface of the high-refractive index material that needs anti-reflection; the other part is a dielectric layer deposited and grown on the surface of the aforementioned sub-wavelength pattern, and the two are integrated to form a laminated sub-wavelength anti-reflection structure . 2. The laminated sub-wavelength anti-reflection structure according to claim 1, wherein the dielectric layer is a uniform single-layer dielectric film, a multi-layer dielectric film, or a dielectric film with a graded refractive index, or a dielectric material In the nanostructure, the material of the medium layer is determined according to the refractive index of the antireflection material required. 3. The laminated sub-wavelength anti-reflection structure according to claim 1, wherein the sub-wavelength pattern is a pattern capable of forming a gradient of refractive index. 4. The preparation method of the laminated sub-wavelength anti-reflection structure according to claim 1, wherein the characteristic steps include: I. Calculate and design the laminated sub-wavelength structure according to the wavelength and angle range of the incident light to be anti-reflection, including the sub-wavelength pattern etched on the high refractive index material for anti-reflection and the sub-wavelength pattern of the dielectric layer formed by deposition; II. Forming a sub-wavelength structural pattern mask on the required anti-reflection high-refractive index material, and forming a sub-wavelength pattern with a corresponding aspect ratio on the substrate by etching; III, removing the mask and cleaning the high refractive index substrate material with sub-wavelength patterns; IV. Growing a dielectric layer on the subwavelength pattern of the substrate, and the material and shape of the dielectric film are calculated according to step I. 5. The method for preparing a laminated sub-wavelength antireflection structure according to claim 4, wherein the method for forming a graphic mask described in step II includes electron beam exposure, coherent lithography and self-assembly, and wherein Etching methods include reactive ion etching, inductively coupled plasma etching, electron cyclotron resonance etching, and wet etching. 6. The method for preparing a laminated sub-wavelength anti-reflection structure according to claim 4, wherein the method for growing the dielectric film in step IV includes magnetron sputtering, pulsed laser deposition, thermal evaporation, and electron beam evaporation , atomic layer deposition, and plasma chemical vapor deposition and self-assembly.

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