Method for manufacturing orthogonal gratings

Abstract

This invention belongs to the field of nanofabrication technology, specifically disclosing a method for fabricating orthogonal gratings. The method includes coating a negative electron resist onto a substrate and curing it to obtain a substrate with a resist layer; performing electron beam exposure on the resist layer using a scanning electron microscope (SEM) with a magnification of 2700 to 6700; and developing and fixing the electron-beam exposed substrate to obtain an orthogonal grating with a frequency of 10000 lines / mm to 25000 lines / mm. This invention utilizes a scanning electron microscope to fabricate high-frequency orthogonal gratings, eliminating the need for a pattern generator, mask, and specialized electron beam lithography system, making the fabrication of high-frequency orthogonal gratings more widespread, convenient, and cost-effective.

Description

Technical Field

[0001] This invention discloses a method for fabricating orthogonal gratings, belonging to the field of nanofabrication technology. Background Technology

[0002] Orthogonal gratings are effective carriers for measuring deformation using electron beam moiré, grid, and geometric phase analysis methods. Their frequency and quality directly affect the sensitivity and accuracy of the test results.

[0003] There are four main methods for fabricating orthogonal gratings on sample surfaces: extreme ultraviolet (EUV) lithography, focused ion beam lithography (FIB), nanoimprint lithography (NIB), and electron beam lithography (EB). Each method has its own advantages and disadvantages, and is suitable for different processing needs and scenarios. EUV lithography provides high-energy light, enabling fine pattern transfer, but is limited by factors such as the stability of the light source, the sensitivity of the photoresist, and the cost of the equipment. FIB offers extremely high resolution and precision, enabling nanoscale pattern fabrication; however, its equipment cost is high, and its production efficiency is relatively low, typically only used for specific high-precision processing needs. NIB boasts advantages such as simple process, low cost, high production efficiency, and the ability to replicate high-resolution patterns; however, the high cost of template fabrication and its susceptibility to damage during use limit its application potential for imprinting gratings on sample surfaces. EB lithography offers advantages such as rapid pattern generation, high resolution, and maskless exposure; however, the equipment used in EB lithography is an electron beam lithography system, resulting in high costs for fabricating orthogonal gratings. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating orthogonal gratings, so as to solve the technical problem of high cost in the existing method of fabricating orthogonal gratings using electron beam lithography.

[0005] This invention provides a method for fabricating orthogonal gratings, comprising:

[0006] A negative electron resist is coated onto the substrate and cured to obtain a substrate with a resist layer;

[0007] The resist layer was subjected to electron beam exposure using a scanning electron microscope with a magnification of 2700 to 6700.

[0008] The substrate exposed by electron beam is developed and fixed to obtain orthogonal gratings with frequencies ranging from 10,000 lines / mm to 25,000 lines / mm.

[0009] Preferably, the scanning electron microscope has a scanning resolution of 1,536 × 1,024 and an accelerating voltage of 18 kV to 22 kV.

[0010] Preferably, the spot size of the electron beam in the scanning electron microscope is 4 to 6.

[0011] Preferably, the residence time of the electron beam in the scanning electron microscope is 60 μs to 140 μs.

[0012] Preferably, a negative electron resist is coated on the substrate, specifically including:

[0013] A negative electron resist with a mass fraction of 5% to 7% is applied to the substrate using a spin coater; the spin coater rotates at a speed of 800 rpm to 1200 rpm and the spin coat time is 50 seconds to 70 seconds.

[0014] Preferably, the curing temperature is 85°C to 95°C, and the curing time is 3 to 5 minutes.

[0015] Preferably, the substrate after electron beam exposure is developed and fixed, specifically including:

[0016] The electron beam exposed substrate is placed in a 2% to 3% tetramethylammonium hydroxide developing solution for 10 to 15 seconds;

[0017] The developed substrate is then fixed in deionized water.

[0018] Preferably, the negative electron resist is composed of silsesquioxane.

[0019] Preferably, before coating and curing the negative electron resist on the substrate, the process further includes:

[0020] Prepare substrates with a roughness of 15 nm to 25 nm;

[0021] A first conductive film layer is disposed on the substrate.

[0022] Preferably, after obtaining an orthogonal grating with a frequency of 10,000 lines / mm to 25,000 lines / mm, the method further includes:

[0023] A second conductive film layer is disposed on the orthogonal grating.

[0024] The method for fabricating orthogonal gratings of the present invention has the following advantages compared with the prior art:

[0025] This invention utilizes a scanning electron microscope to prepare high-frequency orthogonal gratings, eliminating the need for pattern generators, masks, and specialized electron beam lithography systems, thus making the preparation of high-frequency orthogonal gratings more widespread and convenient.

[0026] In the process of exposure using a scanning electron microscope, the present invention requires fewer variable parameters and has a wide range of electron beam dwell time. In other words, the low sensitivity of the exposure dose of HSQ makes the instrument easy to operate, has low technical requirements, and facilitates the precise positioning of high-quality orthogonal gratings on the material surface.

[0027] This invention prepares high-frequency and ultra-high-frequency orthogonal gratings of different frequencies by setting the magnification of the scanning electron microscope and the electron beam spot size during exposure, which can meet the multi-scale requirements in material deformation characterization. Attached Figure Description

[0028] Figure 1 This is a schematic flowchart of the method for fabricating orthogonal gratings in an embodiment of the present invention.

[0029] Figure 2 The image shows the topography of the orthogonal grating with a frequency of 5191 lines / mm prepared according to an embodiment of the present invention.

[0030] Figure 3 The image shows the topography of the orthogonal grating with a frequency of 7416 lines / mm prepared according to an embodiment of the present invention.

[0031] Figure 4 The image shows the topography of an orthogonal grating with a frequency of 10011 lines / mm prepared according to an embodiment of the present invention.

[0032] Figure 5 The image shows the topography of the orthogonal grating with a frequency of 12496 lines / mm prepared according to an embodiment of the present invention.

[0033] Figure 6 The image shows the topography of the orthogonal grating with a frequency of 14832 lines / mm prepared according to an embodiment of the present invention.

[0034] Figure 7 The image shows the topography of the orthogonal grating with a frequency of 17427 lines / mm prepared according to an embodiment of the present invention.

[0035] Figure 8 The image shows the topography of the orthogonal grating with a frequency of 20023 lines / mm prepared according to an embodiment of the present invention.

[0036] Figure 9 The image shows the topography of the orthogonal grating with a frequency of 24843 lines / mm prepared according to an embodiment of the present invention.

[0037] Figure 10 This is a 3D topographic image of an orthogonal grating with a frequency of 10011 lines / mm according to an embodiment of the present invention. Detailed Implementation

[0038] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention can be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the invention with unnecessary detail.

[0039] This invention provides a method for fabricating orthogonal gratings, such as... Figure 1 As shown, the present invention provides a method for fabricating an orthogonal grating, comprising:

[0040] Step 1: Coat the substrate with a negative electron resist and cure it to obtain a substrate with a resist layer.

[0041] In this embodiment of the invention, the substrate needs to be pretreated before step 1 to reduce device performance fluctuations caused by contaminants or interface defects, and to improve the processing accuracy and yield of the grating structure. The pretreatment specifically includes grinding, polishing, and cleaning.

[0042] The surface roughness of the substrate has a significant impact on the quality of the orthogonal grating. Therefore, in this embodiment of the invention, the substrate surface is polished to a roughness of 15nm to 25nm. For example, it can be 15nm, 18nm, 20nm, 22nm, or 25nm, preferably 20nm. Within this roughness range, a high-frequency orthogonal grating with stable performance can be obtained. The substrate used in this embodiment of the invention is a silicon wafer.

[0043] The specific method for cleaning the substrate in this embodiment of the invention is as follows: the substrate is placed in a mixture of acetone and alcohol for ultrasonic cleaning for 10 to 20 minutes to remove contaminants from the substrate surface, and then the substrate is dried to keep it dry.

[0044] To increase the conductivity of the substrate surface and reduce the proximity effect caused by charge accumulation during the fabrication of orthogonal gratings, embodiments of the present invention also provide a first conductive film layer on the cleaned substrate surface, which can be prepared by sputtering gold or platinum.

[0045] This invention involves coating a negative electron resist onto a substrate. Specifically, the negative electron resist is coated onto the first conductive film layer of the substrate after thermal baking. This process includes: applying a negative electron resist with a mass fraction of 5% to 7% onto the substrate using a spin coater; the spin coater speed is 800 rpm to 1200 rpm, preferably 1000 rpm; and the spin coat time is 50 seconds to 70 seconds, preferably 60 seconds. For example, the spin coater described above is a KW-4A model from the Institute of Microelectronics, Chinese Academy of Sciences.

[0046] In the embodiments of the present invention, the mass fraction of the negative electron resist can be 5%, 6% or 7%, preferably 6%. The negative electron resist within this mass fraction range can ensure that subsequent exposure forms a high-resolution pattern, and will not cause excessive reaction due to excessive mass fraction, resulting in line expansion or blurring.

[0047] The aforementioned negative electron resist is preferably HSQ (hydrogen silsesquioxane Polymers), whose main component is hydrogen silsesquioxane. HSQ, as a negative resist, has advantages such as high resolution, low line edge roughness, good corrosion resistance, and stability. Exemplarily, the HSQ powder in this embodiment of the invention is manufactured by AQM Corporation of Canada, and its model is H-SiOx-15.

[0048] In this embodiment of the invention, the curing of a substrate coated with a negative electron resist specifically involves placing the substrate coated with HSQ in an oven for curing at a temperature of 85°C to 95°C, preferably 90°C, for a curing time of 3 to 5 minutes, preferably 4 minutes. After curing, a substrate with a resist layer is obtained.

[0049] Step 2: Use a scanning electron microscope to expose the photoresist layer with an electron beam, where the magnification of the scanning electron microscope is 2700 to 6700.

[0050] The scanning electron microscope in this embodiment of the invention has a scanning resolution of 1,536 × 1,024, an accelerating voltage of 18 kV to 22 kV, preferably 20 kV, an electron beam dwell time of 60 μs to 140 μs, and a working distance of 7 mm to 9 mm, preferably 8 mm.

[0051] Since the negative electron resist used in the embodiments of this invention is HSQ, this application limits the accelerating voltage of the scanning electron microscope to 18kV to 22kV and the residence time of the electron beam to 60μs to 140μs. This avoids excessively high accelerating voltage and excessively long residence time of the electron beam, which would cause the electron beam to penetrate the HSQ resist layer too deeply, leading to an expansion of the forward scattering range, resulting in blurred edges of the developed pattern and a decrease in line width control accuracy. Furthermore, it can also avoid excessively high electron beam energy, which would exacerbate internal scattering within the HSQ resist layer and lead to increased line edge roughness after development.

[0052] To avoid the proximity effect caused by charge accumulation during the fabrication of orthogonal gratings, the spot size of the electron beam in the scanning electron microscope in this embodiment of the invention is 4 to 6.

[0053] The frequency of the orthogonal grating is determined by the magnification of the scanning electron microscope. In this embodiment of the invention, a scanning electron microscope with a scanning resolution of 1,536 × 1,024 is used. Therefore, the relationship between the frequency f (unit: lines / mm) of the orthogonal grating and the magnification M of the electron microscope is: f = 3.708 * M.

[0054] Step 3: Develop and fix the electron beam exposed substrate to obtain orthogonal gratings with frequencies ranging from 10,000 lines / mm to 25,000 lines / mm.

[0055] The above-mentioned development and fixing of the substrate after electron beam exposure specifically includes:

[0056] Step 3.1: Place the electron beam exposed substrate in a tetramethylammonium hydroxide developer solution with a concentration of 2% to 3% and a temperature of 15°C to 25°C for 10 to 15 seconds, preferably 12 seconds.

[0057] For example, the concentration of the above-mentioned tetramethylammonium hydroxide developer can be 2%, 2.38%, 2.5%, 3%, etc., preferably 2.38%; the temperature of the above-mentioned tetramethylammonium hydroxide developer can be 15°C, 20°C, 25°C, etc., preferably 20°C.

[0058] Step 3.2: Quickly immerse the developed substrate in deionized water for fixing. After fixing in deionized water for 5 minutes, remove the substrate and dry it to obtain a high-frequency orthogonal grating with a frequency of 10,000 lines / mm to 25,000 lines / mm.

[0059] To further increase the conductivity of the obtained orthogonal grating and facilitate the observation of the orthogonal grating morphology under a scanning electron microscope, a second conductive film layer is provided on the surface of the orthogonal grating in this embodiment of the invention. The second conductive film layer is prepared by sputtering gold or platinum.

[0060] The preparation parameters and frequencies of the resulting orthogonal gratings in this embodiment of the invention are shown in Table 1.

[0061] Table 1. Fabrication parameters and corresponding orthogonal grating frequencies

[0062]

[0063] As shown in Table 1, the present invention can prepare high-frequency orthogonal gratings with frequencies exceeding 10,000 lines / mm using a common scanning electron microscope. The preparation method is simple and low-cost.

[0064] Figures 2 to 10 The images show the morphology of orthogonal gratings of different frequencies prepared according to embodiments of the present invention. It can be seen that the grating dots are clear and uniform, the grating pitch is consistent, the contrast is high, and the grating quality is high, which can be used for material deformation characterization.

[0065] This invention utilizes a scanning electron microscope to prepare high-frequency orthogonal gratings, eliminating the need for pattern generators, masks, and specialized electron beam lithography systems, thus making the preparation of high-frequency orthogonal gratings more widespread and convenient.

[0066] In the process of exposure using a scanning electron microscope, the present invention requires fewer variable parameters and has a wide range of electron beam dwell time. In other words, the low sensitivity of the exposure dose of HSQ makes the instrument easy to operate, has low technical requirements, and facilitates the precise positioning of high-quality orthogonal gratings on the material surface.

[0067] This invention prepares high-frequency and ultra-high-frequency orthogonal gratings of different frequencies by setting the magnification of the scanning electron microscope and the electron beam spot size during exposure, which can meet the multi-scale requirements in material deformation characterization.

[0068] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for fabricating an orthogonal grating, characterized in that, include: A negative electron resist is coated onto the substrate and cured to obtain a substrate with a resist layer; The resist layer was subjected to electron beam exposure using a scanning electron microscope with a magnification of 4700 to 6700. The substrate exposed by electron beam is developed and fixed to obtain orthogonal gratings with frequencies ranging from 17427 lines / mm to 24843 lines / mm. The negative electron resist has a mass fraction of 5% to 7%, and the negative electron resist is composed of hydrogen silsesquioxane. The development and fixing of the substrate after electron beam exposure specifically includes: The electron beam exposed substrate is placed in a 2% to 3% tetramethylammonium hydroxide developing solution for 10 to 15 seconds. The developed substrate is then fixed in deionized water.

2. The method for fabricating an orthogonal grating according to claim 1, characterized in that, The scanning electron microscope has a scanning resolution of 1,536 × 1,024 and an accelerating voltage of 18 kV to 22 kV.

3. The method for fabricating an orthogonal grating according to claim 2, characterized in that, The spot size of the electron beam in the scanning electron microscope is 4 to 6.

4. The method for fabricating an orthogonal grating according to claim 3, characterized in that, The residence time of the electron beam in the scanning electron microscope is 60 μs to 140 μs.

5. The method for fabricating an orthogonal grating according to claim 1, characterized in that, A negative electron resist is coated onto the substrate, specifically including: A negative electron resist is applied to the substrate using a spin coater; the spin coater rotates at a speed of 800 rpm to 1200 rpm, and the spin coat time is 50 seconds to 70 seconds.

6. The method for fabricating an orthogonal grating according to claim 1, characterized in that, The curing temperature is 85°C to 95°C, and the curing time is 3 to 5 minutes.

7. The method for fabricating an orthogonal grating according to claim 1, characterized in that, Before applying and curing the negative electron resist onto the substrate, the process also includes: Prepare substrates with a roughness of 15 nm to 25 nm; A first conductive film layer is formed on the substrate.

8. The method for fabricating an orthogonal grating according to claim 1, characterized in that, After obtaining orthogonal gratings with frequencies ranging from 10,000 lines / mm to 25,000 lines / mm, the process also includes: A second conductive film layer is disposed on the orthogonal grating.

Images