A multi-stage fine overlay method for complex micro-nano structures

Abstract

A multi-level fine overlay method for complex micro / nano structures belongs to the field of micro / nano fabrication technology. In this method, firstly, based on a double-layer photoresist system, a patterned mask with a precise undercut contour is formed by optimizing the thickness of the upper and lower photoresist layers, spin-coating parameters, and two independent development processes. Then, layer-by-layer overlay alignment is performed within an alignment accuracy range of 800 nm to 3 μm using a global alignment mark set pre-set on the mask mold. Finally, combining magnetron sputtering and precise lift-off processes, high-precision metal or dielectric thin film patterns are transferred without residue, sequentially completing the fabrication of multi-layer micro / nano composite structures. This invention simplifies the process flow, enhances process compatibility, and reduces equipment investment and manufacturing costs while ensuring high-precision integrated manufacturing. It provides a reliable technical path for the mass production of complex micro / nano devices and has broad application prospects in integrated optics, MEMS, and multifunctional sensors.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication technology and relates to a multi-level fine overlay method for complex micro-nano structures. Background Technology

[0002] Complex micro / nano structures are central to realizing next-generation integrated photonic chips, high-end MEMS sensors, and other advanced devices, offering novel device architectures and performance breakthroughs for fields such as information technology and biomedicine. The manufacturing processes used to construct these complex micro / nano structures—multilayer overlay and patterning technologies—are crucial for achieving functional integration and performance optimization. Multilayer overlay technology requires extremely high interlayer alignment accuracy and complete pattern transfer fidelity. Furthermore, due to the multiple cycles involved in the process, the technology itself must possess excellent stability and compatibility to ensure the yield and reliability of the final device. Besides structural complexity, the number of overlay layers and the quality of each pattern directly affect the functional density and performance ceiling of the entire device.

[0003] Currently, the fabrication of micro and nanostructures mostly adopts a step-by-step processing strategy, that is, switching different processing equipment and methods during the fabrication of structures at different scales. In 2013, Chen Guanglu et al., in their paper "Electron Beam and Optical Hybrid Lithography for Nanodevices," successfully fabricated a device with good electrical properties and a minimum gate length of 26 nm using a matched hybrid lithography technique of electron beam direct writing and optical exposure system. In 2025, Li Xinghui et al. from Tsinghua University, in their paper "Cross-Scale Structures Fabrication via Hybrid Lithography for Nanolevel Positioning," constructed an interferometric exposure system that can be adjusted with multiple degrees of freedom, integrating dual-beam interferometric exposure and a high-precision fringe locking system. Through dynamic phase locking, they achieved highly consistent patterning within the region. In 2025, You Zheng et al. from Tsinghua University disclosed a method and device for monitoring plasma dry etching processes based on metasurfaces in Chinese invention patent CN120089612A. This method extracts key structures from the photolithography pattern of the target device and arranges them periodically to form a metasurface. This metasurface is then stitched together with the original pattern before etching, avoiding over-etching or under-etching, thereby improving process controllability and device yield. While this multi-process combination approach achieves cross-scale processing to some extent, it also brings a series of problems: First, the conversion between different processes requires multiple clamping, alignment, and condition adjustments, leading to complex processes, longer cycles, and increased costs. Second, systematic errors and overlay deviations between multiple devices are difficult to control effectively, affecting the alignment accuracy and interface quality of interlayer structures. Furthermore, different processes may have conflicting requirements for material properties and surface conditions, reducing process compatibility and structural reliability.

[0004] Therefore, there is a need for a manufacturing method that can achieve multi-level micro-nano overlay through a set of established process schemes, in order to simplify the process, improve accuracy, enhance compatibility, and promote the further development of multi-layer micro-nano structures in practical applications. Summary of the Invention

[0005] The main technical problem addressed by this invention is overcoming the limitations of existing micro / nano fabrication processes. Current multilayer overlay techniques are constrained by poor single-layer photoresist structure stripping and large cumulative errors in overlay accuracy, typically limiting them to 2-3 layers. This invention proposes a multi-level fine overlay method for complex micro / nano structures. By introducing a dual-layer photoresist system and a dual development process, a patterned mask with a controllable undercut structure is formed, effectively solving the problem of film residue in multilayer fabrication. Simultaneously, a global alignment mark group design significantly improves interlayer overlay accuracy. Combining magnetron sputtering and precise stripping processes, within an alignment accuracy range of 800nm ​​to 3μm, 5 to 7 layers of micro / nano composite structures can be fabricated sequentially using only one standard process framework, providing a reliable technical solution for the integrated manufacturing of complex micro / nano devices.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A multi-level fine overlay method for complex micro / nano structures is disclosed. First, based on a dual-layer photoresist system, a patterned mask with precise undercut contours is formed by optimizing the thickness of the upper and lower photoresist layers, spin-coating parameters, and two independent development processes. Then, layer-by-layer overlay alignment is performed within an alignment accuracy range of 800 nm to 3 μm using a global alignment mark set pre-set on the mask mold. Finally, combining magnetron sputtering and precise lift-off processes, high-precision metal or dielectric thin film patterns are transferred without residue, and the fabrication of multilayer micro / nano composite structures is completed sequentially based on the same process framework. The multi-level fine overlay method includes the following steps:

[0008] Step 1: Pre-treat the substrate to effectively remove tiny particles and oxides from the substrate surface, enhancing the adhesion between the photoresist and the substrate. Specifically:

[0009] Chemical etching was used to pretreat the substrate. In a clean room, acetone was used to ultrasonically clean the substrate for 10-30 minutes at a power of 70W. Then, isopropanol was used to soak the substrate to remove residual acetone for 5-10 minutes. After soaking, the substrate was rinsed with deionized water for 5-10 minutes. Finally, nitrogen was used to dry the substrate.

[0010] Furthermore, the substrate is monocrystalline silicon, silicon nitride, or gallium nitride.

[0011] Step 2: Spin-coating two positive photoresists with different sensitivities onto the substrate surface to obtain a double-layer photoresist film structure; specifically:

[0012] First, remove moisture from the substrate surface; then, using a spin coating method, determine the thickness of the positive photoresist based on the required thickness of the material film, select the spin coating parameters, and spin coat two positive photoresists with different sensitivities. First, spin coat the high-sensitivity positive photoresist, and then spin coat the low-sensitivity positive photoresist to obtain a double-layer photoresist film structure.

[0013] Step 2.1: Before applying positive photoresist, bake the substrate to remove moisture from the substrate surface, making the substrate surface change from hydrophilic to hydrophobic, thereby enhancing the surface adhesion. The baking temperature is 180~200℃ and the baking time is 3~5 minutes.

[0014] Step 2.2, determine the spin coating parameters;

[0015] By using the spin coating method, according to the required thickness of the material film, the corresponding thickness of the positive photoresist is determined according to formula (1), and then the spin coating parameters are selected. The spin coating parameters include spin coating time and rotation speed. The spin coating time is set to 30~40 seconds, and the rotation speed is set to 2500~4000 rpm.

[0016] (1)

[0017] Among them, H PR H represents the total positive photoresist thickness. Film The required thickness of the material film is given by K; K is the safety factor, which ranges from 1.5 to 2.

[0018] Step 2.3: Based on the spin-coating parameters selected in Step 2.2, spin-coat two positive photoresists with different sensitivities. First, spin-coat the high-sensitivity positive photoresist, placing it at the bottom layer to form the base resist. Then, spin-coat the low-sensitivity positive photoresist, placing it at the top layer to form the top resist, ultimately obtaining a double-layer resist film structure. The ratio of the base resist thickness to the top resist thickness is 1.25:1.

[0019] Step 2.4: The residual solvent and moisture in the positive photoresist are completely evaporated by baking the double-layer photoresist film structure, thereby enhancing the adhesion between the positive photoresist and the substrate. The baking temperature is 90~150℃ and the baking time is 2~5 minutes.

[0020] Step 3: Perform mask exposure on the double-layer adhesive film structure formed in Step 2; specifically:

[0021] Step 3.1: When designing the mask layout, plan a set of global alignment marks consisting of high-contrast crosshair structures in the area surrounding the non-functional areas to ensure that they remain intact and easily identifiable in subsequent multi-layer processes.

[0022] The photomask layout includes non-functional regions and functional regions. Functional graphic structures for defining the geometry and size of the micro-nano composite structure are arranged on the functional regions. Other regions outside the functional regions are non-functional regions, including the periphery and gap regions of the photomask layout.

[0023] Step 3.2: Expose the double-layer resist film structure using a photolithography system;

[0024] The photolithography system includes a high-magnification binocular microscope system, capable of finely adjusting the x, y, and x coordinates of the photolithography system. This allows for precise alignment, with an alignment accuracy ranging from 800nm ​​to 3μm.

[0025] Exposure is performed using ultraviolet light with a wavelength of 350nm to 400nm and an exposure power of 450W. Based on the recommended values ​​in the top adhesive data sheet, a reasonable exposure dose range is determined, and the exposure time is calculated using formula (2).

[0026] (2)

[0027] Where T is the exposure time, E best Where is the exposure dose, and P is the exposure power density.

[0028] Step 4: The exposed double-layer photoresist film structure undergoes double development. During development, the high-sensitivity photoresist develops a wider structure compared to the low-sensitivity photoresist, thus forming a photoresist film structure with an undercut structure. Specifically:

[0029] Step 4.1: Perform the first development on the exposed double-layer film structure. Immerse the double-layer film structure completely in the developer for 2-4 seconds. After development, rinse with deionized water and dry with nitrogen gas to form an incompletely developed double-layer film structure.

[0030] Step 4.2: Perform a second development on the incompletely developed double-layer adhesive film structure. Immerse the incompletely developed double-layer adhesive film structure completely in the developer for 2-4 seconds. After development, rinse with deionized water and dry with nitrogen gas to obtain an adhesive film structure with an undercut structure.

[0031] Step 5: Deposit a thin film of material on the undercut film structure; specifically:

[0032] Using a magnetron sputtering device, a thin film of material is sputtered onto the surface of a film structure with an undercut structure, and the sputtering rate is calculated by formula (3);

[0033] (3)

[0034] Where V is the sputtering rate of the target material per unit power, P is the sputtering power of the target material, t is the sputtering time, and d is the thickness of the thin film. This represents the elemental content in the thin film of the material.

[0035] Step 6: The deposited material film is peeled off to remove excess positive photoresist and the material film, yielding the first layer structure; specifically:

[0036] The sputtered substrate is immersed in acetone solution for 3 to 12 hours. Excess photoresist and film are removed by wiping with degreasing cotton. Then, it is immersed in isopropanol for 5 to 10 minutes, and finally rinsed with deionized water for 2 to 3 minutes and dried with nitrogen to obtain the first layer structure.

[0037] Through the preparation process from step one to step six, the first layer of the micro / nano structure is obtained.

[0038] Step 7: Based on the required number of micro / nano structure layers, use the first layer as a new substrate and repeat steps 1 to 6 to prepare each layer of the micro / nano structure in sequence, thereby achieving the integration of multi-level complex micro / nano structures.

[0039] The beneficial effects of this invention are:

[0040] (1) By introducing a double-layer photoresist system and a double development process, the present invention forms a patterned mask with a controllable undercut structure, which effectively optimizes the problem of film breakage and residue during the stripping process and significantly improves the accuracy and edge quality of pattern transfer.

[0041] (2) This invention combines magnetron sputtering and precision stripping processes, and uses a global alignment mark group to achieve interlayer overlay. Within the alignment accuracy range of 800nm ​​to 3μm, 5 to 7 layers of micro-nano composite structures can be prepared sequentially using only one standard process framework.

[0042] In summary, compared with existing manufacturing methods that require multiple process switching, this invention significantly simplifies the process flow, enhances process compatibility, and reduces equipment investment and manufacturing costs while ensuring high-precision integrated manufacturing. It provides a reliable technical path for the mass production of complex micro-nano devices and has broad application prospects in fields such as integrated optics, MEMS, and multifunctional sensors. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the manufacturing method of the present invention;

[0044] Figure 2 This is a schematic diagram of the undercut structure of a double-layer photoresist system;

[0045] Figure 3 This is a schematic diagram of the global alignment mark group on the mask mold.

[0046] Figure 4 This is an optical microscope image of a multilayer micro / nano structure sample.

[0047] Figure 5 This is a TEM image of a cross-section of a multilayer micro / nano structure. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] In this embodiment, a multi-level fine overlay method for complex micro / nano structures is used to fabricate a five-layer structure of tungsten, gold, alumina, GeTe, and alumina. A schematic diagram of the manufacturing process is shown below. Figure 1 As shown. The thickness of titanium is 10nm, the thickness of tungsten is 45nm, the thickness of gold is 200nm, the thickness of the bottom layer of alumina is 30nm, the thickness of GeTe is 30nm, and the thickness of the top layer of alumina is 30nm; LOR 10A photoresist is used as the bottom resist, AZ1500 photoresist is used as the top resist, and a four-inch single crystal silicon wafer is used as the substrate.

[0051] First, the first layer of the micro / nano structure is prepared, specifically:

[0052] Step 1: Pre-treat the substrate to effectively remove tiny particles and oxides from the substrate surface, enhancing the adhesion between the positive photoresist and the substrate. Specifically:

[0053] Chemical etching was used to pretreat the substrate. In a clean room, acetone was used to ultrasonically clean the substrate for 10 minutes at a power of 70W. Then, isopropanol was used to soak the substrate to remove residual acetone for 10 minutes. After soaking, the substrate was rinsed with deionized water for 5 minutes. Finally, nitrogen was used to dry the substrate.

[0054] In this embodiment, the substrate is a four-inch single-crystal silicon wafer with a thickness of 1 mm.

[0055] Step 2: Spin-coating two types of positive photoresist onto the substrate surface to obtain a double-layer photoresist film structure; specifically:

[0056] Step 2.1: Before applying the positive photoresist, bake the substrate to remove moisture from the substrate surface, making the substrate surface change from hydrophilic to hydrophobic, thereby enhancing the surface adhesion. The baking temperature is 180℃ and the baking time is 3 minutes.

[0057] Step 2.2: Spin-coat positive photoresist by spin coating method, with a safety factor of 2. Calculate the required positive photoresist thickness as 400nm according to formula (1). Spin-coat the base coat evenly on the substrate. Set the spinner speed to 3000rpm and the rotation time to 30 seconds.

[0058] Step 2.3: Bake the substrate coated with primer at 130°C for 3 minutes;

[0059] Step 2.4: The top adhesive is evenly spin-coated onto the substrate that has been coated with the base adhesive. The spinner speed is set to 3500 rpm, and the spin time is 30 seconds, resulting in a double-layer adhesive film structure. The double-layer adhesive film structure is then baked at 90℃ for 2 minutes to harden the photoresist, allowing for a tighter adhesion between the double-layer adhesive film structure and the substrate. The ratio of the base adhesive thickness to the top adhesive thickness is 1.25:1.

[0060] Step 3: Perform mask exposure on the double-layer adhesive film structure formed in Step 2; specifically:

[0061] Step 3.1: When designing the mask layout, plan a set of global alignment marks consisting of high-contrast "crosshairs" in the area surrounding the non-functional areas to ensure that they remain intact and easily identifiable in subsequent multi-layer processes.

[0062] The photomask layout includes non-functional regions and functional regions. Functional graphic structures for defining the geometry and size of the micro-nano composite structure are arranged on the functional regions. Other regions outside the functional regions are non-functional regions, including the periphery and gap regions of the photomask layout.

[0063] Step 3.2: Expose the double-layer resist film structure using a photolithography system. The exposure power density of the photolithography machine is 26 mW / cm². 2 The exposure dose was 156 mJ / cm. 2 According to formula (2), the exposure time is calculated to be 6 seconds;

[0064] Step 4: The exposed double-layer photoresist film structure undergoes double development. During development, the high-sensitivity photoresist develops a wider structure compared to the low-sensitivity photoresist, thus forming a photoresist film structure with an undercut structure. Specifically:

[0065] Step 4.1: Perform the first development on the exposed double-layer film structure. Immerse the double-layer film structure completely in the developer for 3 seconds. After development, rinse with deionized water and dry with nitrogen gas to form an incompletely developed double-layer film structure.

[0066] Step 4.2: Perform a second development on the incompletely developed double-layer adhesive film structure. Immerse the incompletely developed double-layer adhesive film structure completely in the developer solution for 3 seconds. After development, rinse with deionized water and dry with nitrogen gas to obtain an adhesive film structure with an undercut structure. A schematic diagram of the adhesive film structure with an undercut structure is shown below. Figure 2 As shown.

[0067] Step 5: Use a magnetron sputtering device to sputter a titanium adhesive layer and a tungsten target onto the substrate with the adhesive film structure. The sputtering power and sputtering time should be calculated according to formula (3) and appropriate values ​​should be taken, where the sputtering rate of the tungsten target is... The magnetron sputtering power was selected as 50W, and the sputtering time was 3300 seconds.

[0068] Step 6: The deposited tungsten film is peeled off and soaked in heated acetone solution for 3 hours, followed by soaking and cleaning with isopropanol and deionized water for 10 minutes, and then dried with nitrogen; a tungsten structure with a minimum linewidth of 17 μm is obtained.

[0069] Using a tungsten structure as a new substrate, a second layer of gold structure for micro / nano structures was fabricated. Specifically:

[0070] Repeat steps one through six. In step three, use the high-magnification binocular microscope system of the ultraviolet lithography system to finely adjust the system's x, y, and... The axis is used to align the global alignment mark set left on the substrate after the first photolithography layer with the global alignment mark set on the mask, followed by exposure to form the gold structure layer resist film structure. A schematic diagram of the global alignment mark set on the mask is shown below. Figure 3 As shown.

[0071] In the fifth step, a gold target is sputtered onto the substrate with the adhesive film structure using a magnetron sputtering device. The sputtering power and sputtering time should be calculated according to formula (3) and appropriate values ​​should be taken, where the sputtering rate of the gold target is... The magnetron sputtering power was selected as 50W, and the sputtering time was 557 seconds.

[0072] In the sixth step, the deposited gold film was peeled off and soaked in a heated acetone solution for 12 hours, followed by rinsing with isopropanol and deionized water for 10 minutes and drying with nitrogen gas; a gold structure with a length and width of 170 μm was obtained.

[0073] Using a gold structure as a new substrate, a third layer of alumina structure with micro / nano structures was fabricated. Specifically:

[0074] Repeat steps one through six. In step three, use the high-magnification binocular microscope system of the ultraviolet lithography system to finely adjust the system's x, y, and... The axis is used to make the global alignment mark group left on the substrate after the second photolithography coincide with the global alignment mark group on the mask mold, and then exposure is performed to form an alumina structure layer film structure.

[0075] In the fifth step, an alumina target is sputtered onto the substrate with the adhesive film structure using a magnetron sputtering device. The sputtering power and sputtering time should be calculated according to formula (3) and appropriate values ​​should be taken, where the sputtering rate of alumina is... The magnetron sputtering power was selected as 120W, and the sputtering time was 7065 seconds.

[0076] In the sixth step, the deposited alumina film was peeled off and soaked in a heated acetone solution for 4 hours, followed by immersion and cleaning in isopropanol and deionized water for 10 minutes, and then dried with nitrogen to obtain an alumina structure with a length and width of 30 μm.

[0077] Using alumina as a new substrate, a fourth-layer GeTe micro / nano structure was fabricated. Specifically:

[0078] Repeat steps one through six. In step three, use the high-magnification binocular microscope system of the ultraviolet lithography system to finely adjust the system's x, y, and... The axis is used to make the global alignment mark group left on the substrate after the third photolithography layer coincide with the global alignment mark group on the mask mold, and then exposure is performed to form the GeTe structure layer film structure.

[0079] In the fifth step, a GeTe target is sputtered onto the substrate with the adhesive film structure using a magnetron sputtering device. The sputtering power and sputtering time should be calculated according to formula (3) and appropriate values ​​should be taken, where the sputtering rate of GeTe is... The magnetron sputtering power was selected as 40W, and the sputtering time was 306 seconds.

[0080] In the sixth step, the deposited GeTe film was peeled off by soaking in a heated acetone solution for 2 hours, followed by rinsing with isopropanol and deionized water for 10 minutes, and then drying with nitrogen to obtain a GeTe structure with a length and width of 10 μm.

[0081] Using GeTe structure as a new substrate, a fifth layer of alumina structure in micro / nano structure was prepared, specifically:

[0082] Repeat steps one through six. In step three, use the high-magnification binocular microscope system of the ultraviolet lithography system to finely adjust the x, y, and x coordinates of the substrate. The axis is used to make the global alignment mark group left on the substrate after the fourth photolithography layer coincide with the global alignment mark group on the mask mold, and then exposure is performed to form an alumina structure layer film structure.

[0083] In the fifth step, an alumina target is sputtered onto the substrate with the adhesive film structure using a magnetron sputtering device. The sputtering power and sputtering time should be calculated according to formula (3) and appropriate values ​​should be taken, where the sputtering rate of alumina is... The magnetron sputtering power was selected as 120W, and the sputtering time was 7065 seconds.

[0084] In the sixth step, the deposited alumina film was peeled off and soaked in a heated acetone solution for 4 hours, followed by immersion and cleaning in isopropanol and deionized water for 10 minutes, and then dried with nitrogen to obtain an alumina structure with a length and width of 30 μm.

[0085] The final prepared multilayer micro / nano structure sample is shown in the optical microscope image. Figure 4 As shown, the TEM image of the structural cross-section is as follows. Figure 5 As shown.

[0086] This embodiment implements a multi-level overlay method for complex micro / nano structures and provides a complete process scheme and key parameter window to ensure a minimum linewidth of 10 μm and an overlay accuracy better than 1.5 μm in the fabrication of a 5-layer composite structure. Through the synergistic design of a double-layer photoresist undercut structure and global alignment marks, combined with an optimized sputtering-lift cycle process, the fabrication of multilayer structures with clear interlayer interfaces, high pattern integrity, and steep edges was successfully achieved. The results are stable and reliable, with strong process compatibility, providing an effective technical path for the integrated fabrication of multilayer complex micro / nano systems.

[0087] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A multi-level fine overlay method for complex micro / nano structures, characterized in that, The multi-level fine overlay method includes the following steps: Step 1: Pre-treat the substrate to remove tiny particles and oxides from the substrate surface and enhance the adhesion between the photoresist and the substrate; Step 2: Spin-coating two positive photoresists with different sensitivities onto the substrate surface to obtain a double-layer photoresist film structure; specifically: First, remove moisture from the substrate surface; then, using a spin coating method, determine the thickness of the positive photoresist based on the required thickness of the material film, select the spin coating parameters, and spin coat two positive photoresists with different sensitivities. First, spin coat the high-sensitivity positive photoresist, and then spin coat the low-sensitivity positive photoresist to obtain a double-layer photoresist film structure. Step 3: Expose the double-layer adhesive film structure formed in step 2 using a mask; Step 4: The exposed double-layer photoresist film structure undergoes double development. During development, the high-sensitivity photoresist develops a wider structure compared to the low-sensitivity photoresist, thus forming a photoresist film structure with an undercut structure; specifically: Step 4.1: Perform the first development on the exposed double-layer film structure. Immerse the double-layer film structure completely in the developer for 2-4 seconds. After development, rinse with deionized water and dry with nitrogen to form an incompletely developed double-layer film structure. Step 4.2: Perform a second development on the incompletely developed double-layer adhesive film structure. Immerse the incompletely developed double-layer adhesive film structure completely in the developer for 2-4 seconds. After development, rinse with deionized water and dry with nitrogen to obtain an adhesive film structure with an undercut structure. Step 5: Deposit a thin film of material on the film structure with an undercut structure; Step 6: The deposited material film is peeled off to remove excess positive photoresist and material film, resulting in the first layer structure; Through the preparation process from step one to step six, the first layer structure of the micro / nano structure is obtained; Step 7: Based on the required number of micro / nano structure layers, using the first layer as a new substrate, repeat steps 1 to 6 to sequentially fabricate each layer of the micro / nano structure, thereby achieving the integration of multi-level complex micro / nano structures.

2. The multi-level fine overlay method for complex micro / nano structures according to claim 1, characterized in that, The first step is specifically as follows: Chemical etching was used to pretreat the substrate. In a clean room, acetone was used to ultrasonically clean the substrate for 10-30 minutes at a power of 70W. Then, isopropanol was used to soak the substrate for 5-10 minutes. After soaking, the substrate was rinsed with deionized water for 5-10 minutes. Finally, nitrogen was used to dry the substrate. The substrate is monocrystalline silicon, silicon nitride, or gallium nitride.

3. The multi-level fine overlay method for complex micro / nano structures according to claim 2, characterized in that, The second step is specifically as follows: Step 2.1: Bake the substrate to remove moisture from the substrate surface, changing the substrate surface from hydrophilic to hydrophobic. The baking temperature is 180~200℃ and the baking time is 3~5 minutes. Step 2.2, determine the spin coating parameters; By using the spin coating method, according to the required thickness of the material film, the corresponding thickness of the positive photoresist is determined according to formula (1), and the spin coating parameters are selected. The spin coating parameters include spin coating time and rotation speed. The spin coating time is set to 30~40 seconds, and the rotation speed is set to 2500~4000 rpm. （1） in, H PR For the total positive photoresist thickness, H Film The required thickness for the material thin film; K For safety margin, a value of 1.5 to 2 is used; Step 2.3: According to the spin coating parameters selected in Step 2.2, spin coat two positive photoresists with different sensitivities. First, spin coat a high-sensitivity positive photoresist to form a base coat, and then spin coat a low-sensitivity positive photoresist to form a top coat. The ratio of the thickness of the base coat to the thickness of the top coat is 1.25:

1. Step 2.4: Bake the double-layer adhesive film structure at a temperature of 90~150℃ for 2~5 minutes.

4. The multi-level fine overlay method for complex micro / nano structures according to claim 3, characterized in that, The third step is specifically as follows: Step 3.1: When designing the mask layout, plan a set of global alignment markers consisting of high-contrast crosshair structures in the area surrounding the non-functional areas; Step 3.2: Expose the double-layer resist film structure using a photolithography system; The lithography system includes a high-magnification binocular microscope system, which uses ultraviolet light for exposure. The exposure dose range is determined according to the recommended values ​​in the top adhesive data sheet, and the exposure time is calculated using formula (2). （2） in, T For the exposure time, E best For exposure dose, P This represents the exposure power density.

5. The multi-level fine overlay method for complex micro / nano structures according to claim 4, characterized in that, In the third step mentioned above: In step 3.1, the mask pattern includes non-functional regions and functional regions. Functional graphic structures for defining the geometry and size of micro-nano composite structures are arranged on the functional regions. Other regions outside the functional regions are non-functional regions, including the periphery and gap regions of the mask pattern. In step 3.2, the photolithography system can finely adjust the x, y, and x coordinates of the photolithography system. The axis achieves precise alignment, with an alignment accuracy range of 800nm ​​to 3μm; the wavelength of the ultraviolet light is 350nm to 400nm, and the exposure power is 450W.

6. The multi-level fine overlay method for complex micro / nano structures according to claim 5, characterized in that, In the fifth step, a thin film of material is sputtered onto the surface of the adhesive film structure with an undercut structure using a magnetron sputtering device, and the sputtering rate is calculated using formula (3). （3） in, V The sputtering rate of the target material per unit power. P For target sputtering power, t Sputtering time, d The thickness of the material film. This represents the elemental content in the thin film of the material.

7. The multi-level fine overlay method for complex micro / nano structures according to claim 6, characterized in that, The sixth step is as follows: Soak the sputtered substrate in acetone solution for 3 to 12 hours, wipe off excess photoresist and film with degreasing cotton, then soak in isopropanol for 5 to 10 minutes, finally rinse with deionized water for 2 to 3 minutes, and dry with nitrogen to obtain the first layer structure.

Images