Preparation Method of Photonic Crystal at the Hundred-Nanometer Scale

Abstract

The present invention relates to the field of preparation of photonic crystals, and particularly to a method for preparing photonic crystals on the order of hundreds of nanometers, comprising: S1. preparing a hard mask on a substrate wafer, uniformly coating a positive photoresist on the hard mask, wherein the thickness of the hard mask is less than or equal to the thickness of the positive photoresist; S2. using an ultraviolet Talbot lithography machine in cooperation with a one-dimensional grating mask to perform multiple under-exposures on the positive photoresist, and then performing post-baking and development on the positively photoresist after multiple under-exposures. Through the superposition of multiple under-exposures, the pattern of the one-dimensional grating mask is changed into the expected pattern of the positive photoresist; S3. etching the hard mask to transfer the expected pattern of the positive photoresist onto the hard mask, thereby obtaining a photonic crystal with an expected lattice shape. This method changes the traditional single exposure into multiple Talbot under-exposures, and adjusts the angle of the mask for each under-exposure, realizing a one-to-many relationship between the mask pattern and the photonic crystal pattern, thereby improving the flexibility of the pattern and reducing the preparation and research and development costs.

Description

Technical Field

[0001] The invention belongs to the technical field of photonic crystal preparation, and in particular relates to a method for preparing a hundred-nanometer-level photonic crystal. Background Art

[0002] At present, the main method for preparing photonic crystals is electron beam lithography. This lithography technology uses a single-point direct writing method, which requires a long time to accumulate high-energy electrons for depth exposure. For the preparation of large-area photonic crystals, a lot of lithography time is required, the preparation efficiency is low, and it also has the inherent disadvantage of high cost. In addition, when preparing large-area photonic crystals, a splicing process is required, which will lead to some inevitable splicing errors, which will seriously affect the performance and yield of the device. It is not suitable for large-scale and large-area production, thus restricting the competitiveness of large-area photonic crystals in the market and seriously hindering their progress from the experimental stage to the market stage.

[0003] In addition, the current main research direction of the relatively low-cost Talbot lithography technology is to improve the photomask structure, but the preparation of photomasks at the hundred-nanometer level is also very expensive. Especially in the process of device development, a large number of different photonic crystal structures are required for experimental demonstration, which requires the purchase of a large number of expensive hundred-nanometer photomasks. Therefore, this one-to-one technology of photomask patterns and photonic crystal structures increases research costs and also wastes social resources invisibly. Summary of the invention

[0004] In view of this, the present invention aims to provide a method for preparing hundred-nanometer photonic crystals to solve the problems of high cost, slow speed, poor flexibility in preparing hundred-nanometer photonic crystals, and the splicing error caused by the single-point direct writing method of electron beam exposure affecting the stability and yield of the device.

[0005] To achieve the above object, the technical solution created by the present invention is implemented as follows:

[0006] A method for preparing a hundred-nanometer photonic crystal comprises the following steps:

[0007] S1. Preparing a hard mask on a substrate sheet, and uniformly coating a positive photoresist on the hard mask; wherein the thickness of the hard mask is less than or equal to the thickness of the positive photoresist;

[0008] S2. Use a UV Taber lithography machine with a one-dimensional grating mask to under-expose the positive photoresist N times, then post-bake and develop the positive photoresist after the N times of underexposure, and transform the pattern of the one-dimensional grating mask into the expected pattern of the positive photoresist by superposition of the N times of underexposure; wherein N≥2;

[0009] S3. Etch the hard mask to transfer the expected pattern of the positive photoresist onto the hard mask, obtaining a photonic crystal with an expected lattice shape.

[0010] Further, during each under-exposure, the one-dimensional grating mask rotates by a preset angle.

[0011] Further, when N = 2, the preset angle is 90° or 60°; when N = 3, the preset angle is 60°.

[0012] Further, when N = 2 and the preset angle is 90°, the expected lattice shape of the photonic crystal is a square; when N = 2 and the preset angle is 60°, the expected lattice shape of the photonic crystal is a rhombus; when N = 3 and the preset angle is 60°, the expected lattice shape of the photonic crystal is a regular hexagon.

[0013] Further, after uniformly coating the positive photoresist on the hard mask and before under-exposure, pre-bake the positive photoresist to make the thickness of the positive photoresist less than 300 nm.

[0014] Further, the positive photoresist is ULTRA-123 photoresist, RZJ-5322 photoresist or PR2000 photoresist.

[0015] Further, the post-bake temperature is 120 °C, the post-bake time is 70 s, and the development time is 60 s.

[0016] Further, the hard mask is a silicon dioxide hard mask, and the silicon dioxide hard mask is prepared on the substrate wafer by plasma-enhanced chemical vapor deposition process.

[0017] Further, use inductively coupled plasma etching process to etch the hard mask.

[0018] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0019] 1. The preparation method provided by the present invention changes the traditional single exposure to multiple Talbot exposures, which improves the preparation accuracy and efficiency of sub-100-nm photonic crystals while reducing the preparation cost.

[0020] 2. Multiple Talbot exposures are all under-exposures, which change the simple one-dimensional grating pattern of the mask into a complex photonic crystal pattern (such as square, rhombus, hexagonal lattice, etc.) through two or more superpositions, expanding the grating from one dimension into the shape of a two-dimensional photonic crystal, achieving the purpose that one mask corresponds to multiple photonic crystal shapes, that is, the mask pattern and the photonic crystal structure achieve one-to-many, greatly improving the flexibility of the photonic crystal pattern and reducing the preparation and R & D costs.

[0021] 3. The present invention can fabricate photonic crystals on the order of hundreds of nanometers using a relatively inexpensive ultraviolet light source, avoiding the problems of slow speed, high cost, and easy occurrence of stitching errors caused by the single-point direct writing method of electron beam lithography. This effectively improves the yield and fabrication efficiency of photonic crystals on the order of hundreds of nanometers, increasing their competitiveness in the market. At the same time, the ultraviolet light source can also be a deep ultraviolet light source or an extreme ultraviolet light source to achieve a higher level of lithography accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not unduly limit the present invention. In the drawings:

[0023] Figure 1 is a schematic diagram of the basic principle of the Talbot lithography technology of the embodiment of the present invention;

[0024] Figure 2 is a schematic flow chart of the method for fabricating photonic crystals on the order of hundreds of nanometers of the embodiment of the present invention;

[0025] Figure 3 is a schematic diagram of fabricating two-dimensional photonic crystals using a one-dimensional grating mask through multiple under-exposures in the embodiment of the present invention;

[0026] Figure 4 is a schematic flow chart of fabricating square lattice photonic crystals using a one-dimensional grating mask through two under-exposures in the embodiment of the present invention;

[0027] Figure 5 is a scanning electron microscope (SEM) image of square lattice photonic crystals after two under-exposures and development in the embodiment of the present invention;

[0028] Figure 6 is a scanning electron microscope (SEM) image of transferring the photoresist pattern to the hard mask after inductively coupled plasma (ICP) etching in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the present invention.

[0030] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention may be combined with each other.

[0031] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0032] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific circumstances.

[0033] To solve the problems of high preparation cost, slow speed, and poor flexibility in the preparation of sub-100-nm photonic crystals, as well as the problem that the stitching error caused by the single-point direct writing method of electron beam lithography affects the stability and yield of devices, the present invention first adopts Talbot lithography technology. This ultraviolet exposure method can avoid the problems of slow speed and high cost caused by the single-point direct writing method of electron beam lithography while achieving the preparation of high-precision photonic crystal structures. Secondly, the Talbot lithography technology adopted is the under-exposure technology of positive photoresist for two or more times. Positive photoresist has the characteristics of being soluble after exposure, having the same pattern as the mask pattern, high resolution, and wide manufacturing applications. By superimposing the one-dimensional grating pattern of the mask plate two or more times to form the expected pattern of the photonic crystal, this multi-time under-exposure method can achieve the purpose of making multiple patterns with one mask plate by adjusting the angle between different exposures, that is, one mask pattern corresponds to multiple photonic crystal structures, greatly improving the flexibility of photonic crystal patterns and reducing the preparation and research costs.

[0034] The basic principle of the method using Talbot lithography is as Figure 1 shown: When the plane wave emitted by the ultraviolet light source passes through the periodic mask plate, the plane wave will propagate along the propagation direction of the light field at At a distance with a period of (where N is a positive integer, P is the period constant of the mask, and λ is the incident wavelength), self-imaging of the periodic object is generated, and at the same time, self-imaging with a π phase shift is generated at a distance with a period of These self-images react with the photoresist through the movement of the substrate along the z-axis. Therefore, the stripe period obtained by exposure will be half of the mask.

[0035] Next, the present invention will be described in detail with reference to Figures 2 - 6 and in combination with embodiments.

[0036] As Figures 2 - 6 shown, an embodiment of the present invention provides a method for preparing a nanometer-scale photonic crystal, including the following steps:

[0037] S1. Prepare a hard mask on the substrate, and uniformly coat a positive photoresist on the hard mask; wherein, the thickness of the hard mask is less than or equal to the thickness of the positive photoresist.

[0038] In the present invention, the hard mask is a silica hard mask, which is prepared on the substrate by using a plasma enhanced chemical vapor deposition (PECVD) process.

[0039] S2. Use an ultraviolet Talbot lithography machine in cooperation with a one-dimensional grating mask to perform N times of under-exposure on the positive photoresist, and then perform post-baking and development on the positive photoresist after N times of under-exposure. Through the superposition of N times of under-exposure, the pattern of the one-dimensional grating mask is changed into the expected pattern of the positive photoresist; wherein, N≥2.

[0040] Innovatively, the present invention adopts the technique of two or more times of under-exposure to superimpose the one-dimensional grating pattern of the mask two or more times into the expected graphic structure (the positive photoresist has positive photoresist properties, and it is easy to be dissolved by the developer in the area where the exposure dose is reached, and it is not easy to be dissolved by the developer in the area where the exposure dose is not reached. Therefore, only the position where multiple under-exposures overlap reaches the exposure dose and is dissolved). As Figure 3 shown, perform the first under-exposure on the one-dimensional grating, and then perform the second exposure after rotating 90°, and a photonic crystal structure with a square lattice can be obtained; or perform the second exposure after rotating 60° after the first under-exposure, and the obtained photonic crystal structure becomes a rhombic lattice; in addition, the two under-exposures can be extended to three under-exposures. After the first under-exposure, rotate 60° to perform the second under-exposure, and then rotate 60° to perform the third under-exposure, and the obtained photonic crystal structure becomes a regular hexagonal lattice. This multiple under-exposure method can achieve the purpose of making multiple photonic crystal patterns with one mask by adjusting the angle of the one-dimensional grating mask between different under-exposures.

[0041] The exposure amount for each underexposure is the same, which is 1 / N of the normal required exposure dose, where N is the expected number of underexposures.

[0042] After uniformly coating a positive photoresist on the silicon dioxide hard mask and before performing underexposure, pre-bake the positive photoresist to make the thickness of the positive photoresist less than 300 nm, so as to obtain a lithography accuracy close to the diffraction limit.

[0043] The quality of the photoresist directly affects the manufacturing accuracy of the semiconductor laser. It is necessary to ensure that the photoresist meets the technical indicators of high resolution, high sensitivity, and high contrast to achieve the accuracy of the expected graphic structure. Therefore, the positive photoresist uses ULTRA-123 photoresist, RZJ-5322 photoresist, or PR2000 photoresist.

[0044] S3. Etch the hard mask to transfer the expected pattern of the positive photoresist onto the hard mask, obtaining a photonic crystal with an expected lattice shape.

[0045] The process of etching the hard mask in the present invention can adopt the inductively coupled plasma (ICP) process.

[0046] Figure 4 Shows the process of preparing a square lattice photonic crystal with a one-dimensional grating mask through two underexposures.

[0047] As Figure 4 shown, the process of preparing a photonic crystal with a square lattice is as follows:

[0048] The first step: Use the PECVD process to prepare a silicon dioxide hard mask on the substrate wafer, and the thickness of the silicon dioxide hard mask is less than or equal to the thickness of the ULTRA-123 photoresist.

[0049] The second step: Coat the ULTRA-123 photoresist on the silicon dioxide hard mask, and require the thickness of the ULTRA-123 photoresist after pre-baking to be less than 300 nm, and use the positive photoresist to achieve high-precision lithography at the nanometer level.

[0050] The third step: Use an ultraviolet Talbot lithography machine to perform the first underexposure (exposure dose ≈ normal required exposure dose / N, where N is the expected number of underexposures, and at this time N = 2); immediately rotate the one-dimensional grating mask by 90° and perform the second underexposure, and the exposure dose should be the same as the first exposure dose.

[0051] The fourth step: Post-bake the positive photoresist after two underexposures at 120 °C for 70 s; then develop it for 60 s, and a square lattice can be obtained on the photoresist (as Figure 5 )

[0052] Step 5: Subsequently, the ICP process is used to etch the silicon dioxide hard mask, transferring the exposed photoresist pattern onto the hard mask, thereby obtaining the desired pattern on the silicon dioxide hard mask (such as Figure 6 ).

[0053] It should be understood that various forms of the processes shown above can be used, with steps reordered, added, or deleted. For example, the steps recited in the disclosure of the present invention can be executed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and no limitation is imposed herein.

[0054] The above specific embodiments do not constitute a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications, combinations, sub - combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a hundred-nanometer photonic crystal, characterized in that: The steps include: S1. Preparing a hard mask on a substrate sheet, and uniformly coating a positive photoresist on the hard mask; wherein the thickness of the hard mask is less than or equal to the thickness of the positive photoresist; S2. Under-exposure the positive photoresist N times using a UV Taber lithography machine in conjunction with a one-dimensional grating mask, and then post-bake and develop the positive photoresist after the N times of underexposure, wherein the one-dimensional grating mask is rotated by a preset angle each time the underexposure is performed, and the pattern of the one-dimensional grating mask is transformed into the expected pattern of the positive photoresist by superposition of the N times of underexposure; wherein N≥2; S3. Etching the hard mask to transfer the expected pattern of the positive photoresist to the hard mask to obtain a photonic crystal with an expected lattice shape.

2. The method for preparing a hundred-nanometer photonic crystal according to claim 1, characterized in that: When N=2, the preset angle is 90° or 60°; when N=3, the preset angle is 60°.

3. The method for preparing a hundred-nanometer photonic crystal according to claim 2, characterized in that: When N=2 and the preset angle is 90°, the expected lattice shape of the photonic crystal is a square; when N=2 and the preset angle is 60°, the expected lattice shape of the photonic crystal is a rhombus; when N=3 and the preset angle is 60°, the expected lattice shape of the photonic crystal is a regular hexagon.

4. The method for preparing a hundred-nanometer photonic crystal according to any one of claims 1 to 3, characterized in that: After the positive photoresist is uniformly coated on the hard mask and before underexposure, the positive photoresist is pre-baked to make the thickness of the positive photoresist less than 300 nm.

5. The method for preparing a hundred-nanometer photonic crystal according to claim 4, characterized in that: The positive photoresist is ULTRA-123 photoresist, RZJ-5322 photoresist or PR2000 photoresist.

6. The method for preparing a hundred-nanometer photonic crystal according to claim 5, characterized in that: The post-baking temperature was 120° C., the post-baking time was 70 s, and the developing time was 60 s.

7. The method for preparing a hundred-nanometer photonic crystal according to claim 1, characterized in that: The hard mask is a silicon dioxide hard mask, and the silicon dioxide hard mask is prepared on the substrate by using a plasma enhanced chemical vapor deposition process.

8. The method for preparing a hundred-nanometer photonic crystal according to claim 1, characterized in that: The hard mask is etched using an inductively coupled plasma etching process.

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