Self-aligned deep ultraviolet lithography method

Abstract

The present disclosure provides a self-aligned deep ultraviolet lithography method, which can be applied to the field of semiconductor technology. The method comprises: preparing a multilayer structure, wherein the multilayer structure comprises: a substrate; a second metal layer arranged on the substrate; a second photoresist layer arranged on the side of the second metal layer away from the substrate; a first metal layer arranged on the side of the second photoresist layer away from the substrate; a hard mask layer arranged on the side of the first metal layer away from the substrate; and a first photoresist layer arranged on the side of the hard mask layer away from the substrate; performing a first lithography process on the first photoresist layer to obtain a first photoresist pattern; using the first photoresist pattern as a mask to form a nanometer grating in the hard mask layer; and performing a second lithography process on the second photoresist layer using the nanometer grating to obtain a second photoresist pattern, wherein the line width of the second photoresist pattern is smaller than the line width of the first photoresist pattern.

Description

Technical Field

[0001] This disclosure relates to the field of semiconductor technology, and more specifically, to a deep ultraviolet lithography method. Background Technology

[0002] Photolithography is a key process in chip manufacturing. The ever-increasing demands for semiconductor chip integration have strongly driven the development of photolithography technology. When using traditional optical systems to project and transfer lithographic patterns, the linewidth is limited by the diffraction limit. Achieving super-diffraction-limited lithography methods that meet current nanoscale linewidth requirements while simultaneously reducing processing costs is of great significance to the development and application of microelectronics technology.

[0003] According to Rayleigh's criterion, the spatial resolution of an imaging optical system is x≈0.61λ / NA, where λ is the wavelength of the incident light and NA is the numerical aperture of the optical system. Traditional optical systems cannot achieve imaging of structures at half wavelength scale. To achieve narrower linewidths in lithography processes, extreme ultraviolet (EUV) light sources are required, but EUV technology is quite challenging. Developing deep ultraviolet (DEU) lithography technology is beneficial to the development of semiconductor lithography technology. Among these challenges, overcoming the diffraction limit is crucial. In 2000, Pendry proposed the concept of a superlens based on negative refractive index materials [Pendry, JB, Physical Review Letters, 2000.85(18): p.3966-3969.]. Theoretical studies have shown that negative refractive index materials can enhance evanescent fields. Negative refractive index materials require both negative dielectric constant and negative permeability, and strictly speaking, such materials do not exist in nature. However, by utilizing the structures of artificial metamaterials and metasurfaces, equivalent media with negative refractive properties can be generated [Shelby, RA, DRSmith, and S. Schultz, Science, 2001, 292(5514): p.77-79.]. Under the quasi-static approximation, noble metals such as gold and silver have negative dielectric constants and can achieve the superlens effect under the action of p-polarized light. Based on Pendry's theory, researchers further proposed superlens lithography, which can achieve periodic pattern lithography with a period of 140 nm in the near field under the incident condition of g-line light source (436 nm) using a 25 nm thick NiCr mask [Alkaisi, MM, et al., Applied Physics Letters, 1999, 75(22): p.3560-3562.]. In 2006, Jacob et al. proposed the Hyperlens scheme based on hyperbolic dispersive metamaterials [Jacob, Z., L.V. Alekseyev, and E. Narimanov, Optics Express, 2006, 14(18): 8247-8256.]. This scheme uses a periodic structure of cylindrical film layers to replace the planar multilayer film structure, which completes the function of shrinking the image and realizes super-resolution imaging. SPP interferometric exposure technology has the potential advantage of realizing large-scale nanofabrication. As a photonics technology, it does not have the space charge effect, and compared with direct writing technology, it can quickly complete the large-area pattern transfer in one go. At the same time, as an optical near-field technology, it can overcome the absolute limitation of the diffraction limit on the processing linewidth. In recent years, researchers at home and abroad have carried out relevant research on SPP interferometric exposure technology.In 2004, Luo, XG, et al. first proposed a photolithography method for achieving subwavelength dimensions based on the SPP resonance effect, which theoretically could achieve a spatial resolution of 50 nm based on visible or ultraviolet light sources [Luo, XG and T. Ishihara, Optics Express, 2004.12(14): 3055-3065.]. In 2005, Professor Xiang Zhang's research group at the University of California, Berkeley, experimentally verified that a superlens based on a silver thin film structure could achieve a spatial resolution of 60 nm linewidth, approximately 1 / 6 of the incident light wavelength [Fang, N., et al., Science, 2005.308(5721): 534-537.]. Since then, many research institutions at home and abroad have conducted a series of studies on photolithography methods based on structures such as metal thin film superlenses, SPP waveguides, and metal nanocavities, aiming to further improve the processing linewidth, exposure depth of field, and interference fringe contrast.

[0004] However, achieving ultra-narrow linewidth lithography in the deep ultraviolet (EUV) band remains an unsolved problem. Given the significant challenges, bottlenecks, and severe technological blockades associated with EUV lithography, developing ultra-narrow linewidth EUV lithography methods is crucial for overcoming technological monopolies and blockades, and for promoting the development of the microelectronics industry. Summary of the Invention

[0005] In view of this, embodiments of the present disclosure provide a self-aligned deep ultraviolet lithography method, which is based on deep ultraviolet lithography technology and can prepare ultra-narrow linewidth photoresist patterns while reducing equipment modification costs.

[0006] According to one aspect of this disclosure, a self-aligned deep ultraviolet lithography method is provided, characterized by comprising the following steps: fabricating a multilayer structure, wherein the multilayer structure comprises: a substrate; a second metal layer disposed on the substrate; a second photoresist layer disposed on a side of the second metal layer away from the substrate; a first metal layer disposed on a side of the second photoresist layer away from the substrate; a hard mask layer disposed on a side of the first metal layer away from the substrate; and a first photoresist layer disposed on a side of the hard mask layer away from the substrate; performing a first lithography process on the first photoresist layer to obtain a first photoresist pattern; using the first photoresist pattern as a mask to form a nanograting in the hard mask layer; and performing a second lithography process on the second photoresist layer using the nanograting to obtain a second photoresist pattern. The second photoresist pattern, wherein the second photoresist pattern is obtained by performing a second photolithography process on the second photoresist layer using the nanograting, specifically includes: irradiating the nanograting and the surface plasmon waveguide with incident light in the deep ultraviolet band, wherein the surface plasmon waveguide includes a first metal layer, a second photoresist layer, and a second metal layer; the nanograting diffracts the incident light in the deep ultraviolet band to obtain a diffraction order; the diffraction order is excited in the surface plasmon waveguide to form a surface plasmon waveguide mode; the second photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode; and the second photoresist layer is developed to obtain the second photoresist pattern, wherein the linewidth of the second photoresist pattern is smaller than the linewidth of the first photoresist pattern.

[0007] According to an embodiment of this disclosure, the excitation of a surface plasmon waveguide mode by the diffraction order in the surface plasmon waveguide includes: using a higher-order diffraction order to excite a surface plasmon waveguide mode in the surface plasmon waveguide, wherein the higher-order diffraction order includes diffraction orders greater than or equal to 3.

[0008] According to embodiments of this disclosure, performing a first photolithography process on the first photoresist layer to obtain a first photoresist pattern includes:

[0009] The first photolithography process is performed on the first photoresist layer using incident light in the deep ultraviolet band to obtain the first photoresist pattern.

[0010] According to embodiments of this disclosure, the wavelength range of the incident light in the deep ultraviolet band includes 157 nm to 365 nm.

[0011] According to embodiments of this disclosure, the wavelength range of the incident light in the deep ultraviolet band includes 193 nm to 266 nm.

[0012] According to an embodiment of this disclosure, performing a first photolithography process on the first photoresist layer using incident light in the deep ultraviolet band includes performing an immersion photolithography process on the first photoresist layer using incident light with a wavelength of 193 nm.

[0013] According to an embodiment of this disclosure, performing a second photolithography process on the second photoresist layer using the nanograting includes: performing an immersion photolithography process on the second photoresist layer using the nanograting based on incident light with a wavelength of 193 nm.

[0014] According to embodiments of this disclosure, the materials of the second metal layer and the first metal layer are selected to be materials whose real part of dielectric constant is negative in the deep ultraviolet band.

[0015] According to embodiments of this disclosure, the nanograting is a one-dimensional periodic structure or a two-dimensional periodic structure.

[0016] According to embodiments of this disclosure, the period of the nanograting is equal to an integer multiple of the effective wavelength of the surface plasmon waveguide mode, the integer being equal to the order of the diffraction order, and the order of the diffraction order is an integer greater than or equal to 3.

[0017] According to embodiments of this disclosure, the period of the nanograting is less than or equal to 110 nm.

[0018] According to embodiments of this disclosure, the period of the nanograting is 40 nm to 110 nm.

[0019] According to embodiments of this disclosure, the duty cycle of the nanograting is 20%-80%, the thickness of the nanograting is 10-40 nm, and the thickness of the first metal layer is 0-20 nm.

[0020] According to embodiments of this disclosure, the thickness of the second photoresist layer is 10 nm to 20 nm.

[0021] According to embodiments of this disclosure, the thickness of the second photoresist layer is 10 nm to 15 nm.

[0022] According to an embodiment of this disclosure, the ratio of the linewidth of the second photoresist pattern to the linewidth of the first photoresist pattern is less than 1 / 10.

[0023] According to embodiments of this disclosure, the second photoresist pattern includes a pattern with a linewidth of less than or equal to 10 nm.

[0024] According to embodiments of this disclosure, the second photoresist pattern includes a pattern with a linewidth of 7 to 10 nm.

[0025] The self-aligned deep ultraviolet lithography method provided in this disclosure replaces the extreme ultraviolet lithography machine with a deep ultraviolet lithography machine, achieving nanoscale linewidth requirements while reducing the equipment and cost requirements of the lithography method. A nanograting is fabricated in situ using a self-aligned method, and the incident deep ultraviolet light source is diffracted and coupled into a surface plasmon waveguide mode using the nanograting. The compression effect of the light field by the surface plasmon waveguide mode is then used to fabricate ultra-narrow linewidth photoresist patterns, significantly reducing the need for modifications to the deep ultraviolet lithography equipment. Furthermore, compared to conventional deep ultraviolet lithography techniques, the self-aligned deep ultraviolet lithography method provided in this disclosure avoids complex multi-step exposure processes and reduces grating defects. Attached Figure Description

[0026] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings. Obviously, the drawings described below are some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any creative effort. In the drawings:

[0027] Figure 1 A flowchart illustrating a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure is shown schematically.

[0028] Figure 2 The flowchart illustrates a method for performing a second photolithography process on the second photoresist layer using the nanograting in a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure to obtain a second photoresist pattern.

[0029] Figure 3 A schematic front view of a multilayer structure for a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure is shown.

[0030] Figure 4 The diagram illustrates a multilayer structure after deep ultraviolet lithography exposure and development of the first photoresist layer.

[0031] Figure 5 A schematic front view of a multilayer structure containing nanogratings is shown.

[0032] Figure 6 The diagram schematically shows a front view of a multilayer structure containing a nanograting illuminated by incident light in the deep ultraviolet band.

[0033] Figure 7 A schematic front view of the multilayer structure with the nanograting and the first metal layer stripped off is shown.

[0034] Figure 8 The diagram schematically shows a front view of the multilayer structure after the second photoresist layer has been developed.

[0035] Figure 9 The schematic diagram illustrates the light field intensity distribution inside the second photoresist layer during surface plasmon interference exposure, as exemplified by this disclosure.

[0036] Figure 10 The diagram schematically illustrates the light field distribution curve at the center of the second photoresist layer, a specific example of this disclosure.

[0037] Reference numerals: 1-substrate; 2-second metal layer; 3-second photoresist layer; 4-first metal layer; 5-hard mask layer; 6-first photoresist layer; 7-first photoresist pattern; 8-nano grating; 9-incident light; 10-second photoresist pattern. Detailed Implementation

[0038] To make the above-disclosed objects, features, and advantages more apparent and understandable, specific embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0040] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0041] When using expressions such as "at least one of A, B, and C," it should generally be interpreted in accordance with the meaning commonly understood by those skilled in the art (e.g., "having at least one of A, B, and C" should include, but is not limited to, having A alone, having B alone, having C alone, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, features defined with "first" or "second" may explicitly or implicitly include one or more of the stated features.

[0042] Linewidth, typically referring to the minimum channel width achievable in integrated circuit manufacturing processes, is a key indicator of the advancement of integrated circuit technology. Smaller linewidths result in higher integration density, allowing for the integration of more circuit units within the same area. With the increasing demands for semiconductor chip integration density, reducing linewidth is crucial for the development and application of microelectronics technology. When using traditional optical systems to project and transfer lithographic patterns, the linewidth is limited by the diffraction limit. To achieve narrower linewidths in lithography, extreme ultraviolet (EUV) light sources are required. EUV typically refers to ultraviolet light with wavelengths ranging from 10 to 121 nm in the electromagnetic spectrum. In EUV lithography, 10–14 nm EUV light is commonly used as the light source, enabling the fabrication of linewidths below 10 nm. Due to the high technical difficulty and cost of EUV technology, and the resulting technological blockade, the development of deep ultraviolet (DUV) lithography has become a research hotspot. DUV typically refers to ultraviolet light with wavelengths ranging from 157 to 365 nm. Currently, in deep ultraviolet lithography, how to break through the diffraction limit and achieve ultra-narrow linewidth lithography in the deep ultraviolet band remains a problem to be solved.

[0043] In one exemplary embodiment of this disclosure, a self-aligned deep ultraviolet lithography method is provided.

[0044] Figure 1 A flowchart illustrating a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure is shown schematically.

[0045] like Figure 1 As shown, the self-aligned deep ultraviolet lithography process of this embodiment includes operations S101 to S104.

[0046] In operation S101, a multilayer structure is fabricated, wherein the multilayer structure includes: a substrate; a second metal layer disposed on the substrate; a second photoresist layer disposed on the side of the second metal layer away from the substrate; a first metal layer disposed on the side of the second photoresist layer away from the substrate; a hard mask layer disposed on the side of the first metal layer away from the substrate; and a first photoresist layer disposed on the side of the hard mask layer away from the substrate.

[0047] In operation S102, a first photolithography process is performed on the first photoresist layer to obtain a first photoresist pattern.

[0048] In operation S103, a nanograting is formed in the hard mask layer using the first photoresist pattern as a mask.

[0049] In operation S104, the second photolithography process is performed on the second photoresist layer using the nanograting to obtain the second photoresist pattern.

[0050] from Figure 1As can be seen from the embodiments of this disclosure, a two-step exposure method is used. In the first exposure, a nanograting is prepared in situ, and in the second exposure, the nanograting is used to perform a photolithography process and obtain the final required second photoresist pattern. The first and second exposures do not affect each other and do not require spatial alignment. This simplifies the process, reduces equipment modifications, and effectively avoids the problems of high cost and numerous grating defects and impurities caused by first using electron beam etching to prepare the nanograting and then using the nanograting to perform a photolithography process.

[0051] In operation S103, an etching technique can be used to fabricate a nanograting. The etching technique can be a conventional etching process, such as dry etching. A preferred etching depth is 10-50 nm, more preferably 30-50 nm.

[0052] The second photolithography process in operation S104 also includes the step of using a nanograting to diffract the incident light in the deep ultraviolet band to excite and form a surface plasmonic waveguide mode in the surface plasmonic waveguide, thereby realizing the surface plasmonic interference lithography of the second photoresist layer.

[0053] Figure 2 The flowchart illustrates a method for performing a second photolithography process on the second photoresist layer using the nanograting in a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure to obtain a second photoresist pattern.

[0054] like Figure 2 As shown, the method S104 of this embodiment, which uses the nanograting to perform a second photolithography process on the second photoresist layer to obtain a second photoresist pattern, further includes operations S1041 to S1045.

[0055] In operation S1041, the nanograting and surface plasmon waveguide are irradiated with incident light in the deep ultraviolet band, wherein the surface plasmon waveguide includes the first metal layer, the second photoresist layer and the second metal layer.

[0056] In operation S1042, the nanograting diffracts the incident light in the deep ultraviolet band to obtain a diffraction order.

[0057] In operation S1043, the diffraction order is excited in the surface plasmon waveguide to form a surface plasmon waveguide mode.

[0058] In operation S1044, the second photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode.

[0059] In operation S1045, the second photoresist layer is developed to obtain a second photoresist pattern, wherein the linewidth of the second photoresist pattern is smaller than the linewidth of the first photoresist pattern.

[0060] In the embodiments of this disclosure, it should be understood that the nanograting has a periodic structure. When the nanograting is irradiated with deep ultraviolet incident light, the incident light in the deep ultraviolet band of the nanograting diffracts and generates diffracted waves of different orders, i.e., diffraction orders. In the embodiments of this disclosure, a surface plasmon waveguide is constructed by introducing a first metal layer, a second photoresist layer, and a second metal layer. The first metal layer and the second photoresist layer have opposite dielectric constants, and the second photoresist layer and the second metal layer also have opposite dielectric constants. When the diffraction orders enter the surface plasmon waveguide, surface plasmon polaritons can be excited at the interface between the first metal layer and the second photoresist layer, and at the interface between the second photoresist layer and the first metal layer. Since the first metal layer and the second metal layer form a surface plasmon resonant cavity, it can significantly change and modulate the wave vector of the surface plasmon polaritons, thereby forming a surface plasmon waveguide mode that propagates in opposite directions, and using the surface plasmon waveguide mode to form interference fringes in the second photoresist layer. The effective wavelength of the surface plasmon waveguide mode is equal to 2π divided by the propagation constant of the surface plasmon waveguide mode. Its wavelength is much smaller than the incident light wavelength. Therefore, the above method can obtain interference fringe resolution beyond the diffraction limit, and thus obtain a second photoresist pattern with ultra-narrow linewidth.

[0061] Preferably, the ratio of the linewidth of the second photoresist pattern to the linewidth of the first photoresist pattern is less than 1 / 10.

[0062] Figure 3 A schematic front view of a multilayer structure for a self-aligned deep ultraviolet lithography method according to an embodiment of the present disclosure is shown.

[0063] exist Figure 3In this self-aligned deep ultraviolet lithography multilayer structure, a substrate 1, a second metal layer 2, a second photoresist layer 3, a first metal layer 4, a hard mask layer 5, and a first photoresist layer 6 are included. The substrate 1 can be any substrate known in the art, including but not limited to single-crystal silicon substrates, silicon nitride, metal substrates, silicon oxide substrates, glass substrates, sapphire, and III-V group substrates. In the embodiments of this disclosure, when fabricating the multilayer structure, a metal thin film can be prepared on the substrate 1 using a vacuum deposition method, for example, electron beam evaporation. The metal thin film can be prepared by electron beam evaporation as the second metal layer 2. Further, a second photoresist layer 3 can be prepared on the surface of the second metal layer 2 by spin coating. A metal thin film is then prepared again using electron beam evaporation to obtain a first metal layer 4 adjacent to the second photoresist layer 3 and a hard mask layer 5 above the first metal layer 4. It should be noted that the materials of the first metal layer 4 and the hard mask layer 5 can be the same or different. When the first metal layer 4 and the hard mask layer 5 are made of the same material, a layer of a certain thickness close to the second photoresist layer 3 can be used as the first metal layer 4 in the multilayer structure after electron beam evaporation deposition, and the remaining thickness can be used as the hard mask layer 5. When the first metal layer 4 and the hard mask layer 5 are made of different materials, the first metal layer 4 can be deposited first, followed by the hard mask layer 5. Furthermore, a first photoresist layer 6 can be prepared again on the hard mask layer 5 by spin coating to complete the fabrication of the multilayer structure. It should be understood that the multilayer structure is used to fabricate a second photoresist pattern with ultra-narrow linewidths, and each layer is nanoscale.

[0064] According to embodiments of this disclosure, the excitation of a surface plasmon waveguide mode (SPL) by the diffraction order in the SPL includes: using a higher-order diffraction order to excite the SPL mode in the SPL, wherein the higher-order diffraction order includes diffraction orders greater than or equal to 3. Using a higher-order diffraction order to excite the SPL mode can increase the period of the nanograting, thereby reducing the fabrication difficulty of the nanograting. The utilization of the higher-order diffraction order can be achieved by adjusting the parameters of the SPL, such as the thickness of the second photoresist, and the materials of the first and second metal layers.

[0065] According to embodiments of this disclosure, performing a first photolithography process on the first photoresist layer to obtain a first photoresist pattern includes: performing a first photolithography process on the first photoresist layer using incident light in the deep ultraviolet band to obtain the first photoresist pattern. In embodiments of this disclosure, the first photolithography process and the second photolithography process can use the same light source to simplify the process and enable the entire process flow to be fully realized using deep ultraviolet lithography technology.

[0066] According to embodiments of this disclosure, the self-aligned deep ultraviolet lithography method is based on incident light in the deep ultraviolet band, wherein the wavelength range of the incident light in the deep ultraviolet band includes 157 nm to 365 nm. In some specific embodiments, the wavelength range of the incident light in the deep ultraviolet band includes 193 nm to 266 nm. In some preferred embodiments, the wavelength of the incident light in the deep ultraviolet band can be common light sources such as 193 nm or 266 nm.

[0067] According to embodiments of this disclosure, performing a first photolithography process on the first photoresist layer using incident light in the deep ultraviolet band includes performing an immersion photolithography process on the first photoresist layer using incident light with a wavelength of 193 nm. Similarly, performing a second photolithography process on the second photoresist layer using the nanograting includes performing an immersion photolithography process on the second photoresist layer using the nanograting based on incident light with a wavelength of 193 nm. During the first photolithography process, an immersion layer may be formed on the side of the first photoresist layer away from the substrate. Similarly, during the second photolithography process, an immersion layer may be formed on the side of the nanograting away from the substrate. The material of the immersion layer may include one of water, air, oil, and silicon dioxide.

[0068] According to embodiments of this disclosure, the materials of the lower metal layer 2 and the upper metal layer 4 are selected to have a negative real part of the dielectric constant in the deep ultraviolet band. It should be understood that the upper metal layer 4 and the lower metal layer 2 are made of the same material, including but not limited to at least one of aluminum, magnesium, or magnesium-aluminum alloys. When the hard mask layer 5 is made of a different material than the upper metal layer 4, the hard mask layer 5 can also be a silicon thin film.

[0069] It should be understood that the first photoresist pattern in the embodiments of this disclosure is used as a mask for fabricating a nanograting. The first photoresist pattern should have a similar structure to the nanograting. To achieve surface plasmon interference exposure for the second photoresist layer, the first pattern includes a periodic structure, such as a one-dimensional periodic structure, a two-dimensional periodic structure, etc. Correspondingly, the nanograting can be a one-dimensional periodic structure or a two-dimensional periodic structure. In some embodiments of this disclosure, to reduce the fabrication difficulty of the nanograting while exciting the surface plasmon waveguide mode, a nanograting with a larger period can be fabricated using a higher-order diffraction order. The period of the nanograting is equal to an integer multiple of the effective wavelength of the surface plasmon waveguide mode, and the integer is equal to the order of the diffraction order. Preferably, the order of the diffraction order is an integer greater than or equal to 3. Embodiments of this disclosure preferably fabricate nanogratings with a period less than or equal to 110 nm to obtain a second photoresist pattern with an ultra-narrow linewidth. More preferably, the period of the nanograting is 40 nm to 110 nm. Furthermore, parameters other than the period of the nanograting can be optimized to achieve efficient coupling of the surface plasmon waveguide mode. For example, structural parameters such as the duty cycle, thickness, and first metal layer thickness of the nanograting can be optimized. Preferably, the duty cycle of the nanograting can be 20%-80%, the thickness of the nanograting can be 10-40 nm, and the thickness of the first metal layer is 0-20 nm. For example, the duty cycle of the nanograting can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.; the thickness of the nanograting can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, etc.; and the thickness of the first metal layer can be 5 nm, 10 nm, 15 nm, 20 nm, etc. The specific selection of the above structural parameters can be adjusted according to the incident light wavelength to efficiently couple the surface plasmon waveguide mode. Furthermore, the thickness of the second photoresist layer can also be optimized to obtain an ultra-narrow linewidth. Preferably, the thickness of the second photoresist layer can be 10-20 nm, and more preferably, the thickness of the second photoresist layer can be 10-15 nm.

[0070] In some embodiments, the second photoresist pattern includes a pattern with a linewidth of less than or equal to 10 nm.

[0071] In some embodiments, the second photoresist pattern includes a pattern with a linewidth of 7 to 10 nm.

[0072] The following is combined Figures 4 to 10 This disclosure describes in detail a specific example of a self-aligned deep ultraviolet lithography method. It should be understood that the following description is merely illustrative and not a specific limitation of this disclosure.

[0073] The specific example of the self-aligned deep ultraviolet lithography method disclosed herein includes steps S1 to S6.

[0074] Step S1: Fabrication of a multilayer structure. Substrate 1 is a single-crystal silicon substrate. A 50nm aluminum, magnesium, or magnesium-aluminum alloy thin film is prepared as the second metal layer 2 using electron beam evaporation. Then, a 15nm thick second photoresist layer 3 is prepared on the surface of the second metal layer 2 using spin coating. Another 50nm metal thin film is prepared using electron beam evaporation. A 10nm metal thin film adjacent to the second photoresist layer 3 serves as the first metal layer 4 in the multilayer structure, and the remaining 40nm metal thin film serves as the hard mask layer 5. A 70nm thick first photoresist layer 6 is prepared again using spin coating to complete the fabrication of the multilayer structure. The hard mask layer 5 and the first metal layer 4 are made of the same material, selected from aluminum, magnesium, or a magnesium-aluminum alloy. It should be understood that the first metal layer 4 and the second metal layer 2 are made of the same material. Note that different materials can also be selected for the preparation of the first metal layer 4 and the hard mask layer 5. For example, the first metal layer 4 can be selected from aluminum, magnesium, or a magnesium-aluminum alloy. The hard mask layer 5 is a silicon thin film.

[0075] Step S2: The first photoresist layer 6 is exposed and developed using an immersion deep ultraviolet lithography process with a wavelength of 193nm to obtain the first photoresist pattern 8.

[0076] Figure 4 The diagram schematically shows a front view of a multilayer structure after deep ultraviolet lithography exposure and development of the first photoresist layer.

[0077] like Figure 4 As shown, the multilayer structure after deep ultraviolet lithography exposure and development of the upper photoresist layer includes a substrate 1, a second metal layer 2, a second photoresist layer 3, a first metal layer 4, a hard mask layer 5, and a first photoresist pattern 7. It should be understood that the first photoresist pattern 7 is the structure of the first photoresist layer 6 after exposure and development. In a specific example of this disclosure, the first photoresist pattern 7 is a one-dimensional periodic structure with a period of 110 nm and a duty cycle of 1.75, meaning the width of the retained strip-shaped upper photoresist layer is 70 nm, and the width of the area where the upper photoresist layer is removed is 40 nm.

[0078] In step S3, after obtaining the first photoresist pattern 7, a nanograting is fabricated on the hard mask layer 5 using the first photoresist pattern 7 as a mask and an etching technique is employed. In the example disclosed herein, the hard mask layer can be etched by 40 nm to obtain a nanograting with a period of 110 nm, which facilitates efficient excitation of surface plasmon waveguide modes.

[0079] Figure 5 A schematic front view of a multilayer structure containing nanogratings is shown.

[0080] like Figure 5 As shown, the multilayer structure containing the nanograting includes a substrate 1, a second metal layer 2, a second photoresist layer 3, a first metal layer 4, and a nanograting 8. It should be understood that the nanograting 8 is the structure formed after etching the hard mask layer 5. After etching, the first photoresist pattern 7 is also removed.

[0081] Step S4 involves irradiating the multilayer structure containing the nanograting 8 using an immersion deep ultraviolet lithography process with a wavelength of 193 nm. The resulting third-order diffraction order is then coupled into a surface plasmonic waveguide mode that propagates in opposite directions, forming interference fringes in the second photoresist layer 3, thus completing the surface plasmonic interference exposure.

[0082] Figure 6 A schematic diagram illustrates a front view of a multilayer structure containing a nanograting illuminated by incident light in the deep ultraviolet band. The multilayer structure includes a substrate 1, a second metal layer 2, a second photoresist layer 3, a first metal layer 4, and a nanograting 8. When the multilayer structure is illuminated perpendicularly by incident light 9, the nanograting 8 diffracts the incident light 9, generating diffraction orders and exciting counter-propagating surface plasmon waveguide modes, forming interference fringes in the second photoresist layer 3.

[0083] Further, in step S5, the nanograting 8 and the first metal layer 4 are peeled off using a stripping process, leaving the second photoresist layer 3. In step S6, the second photoresist layer 3 is developed to obtain a second photoresist pattern 10, wherein the linewidth of the second photoresist pattern 10 is approximately equal to half the period of the interference fringes generated in the second photoresist layer 3. In a specific example of this disclosure, interference fringes with a period of 18.2 nm can be obtained, and a second photoresist pattern 10 with a linewidth of 9.1 nm can be further obtained.

[0084] Figure 7 A schematic front view of a multilayer structure with the nanograting and first metal layer stripped away is shown. Figure 7 In the process, the multilayer structure with the nanograting 8 and the first metal layer 4 stripped off includes a substrate 1, a second metal layer 2, and a second photoresist layer 3.

[0085] Figure 8 A schematic diagram shows a front view of the multilayer structure after development of the second photoresist layer. Figure 8 In the process, the multilayer structure after developing the second photoresist layer includes a substrate 1, a second metal layer 2, and a second photoresist pattern 10. It should be understood that the second photoresist pattern 10 is the remaining portion after developing the second photoresist layer 3. Furthermore, the pattern in the second photoresist pattern 10 can be transferred to the second metal layer 2 by etching, and the pattern in the second metal layer 2, which serves as a metal mask, can be further transferred to the substrate 1 by etching.

[0086] To verify the feasibility of the self-aligned deep ultraviolet lithography process of the embodiments of this disclosure, numerical simulations based on the finite element method were performed on the surface plasmon interference exposure process of the embodiments of this disclosure. The optical parameters of each part of the example of this disclosure used for simulation verification are as follows: the photoresist refractive index is 1.7, the dielectric constants of the first metal layer 4, the second metal layer 2, and the hard mask layer 5 are all -4, and the immersion layer material of the immersion deep ultraviolet lithography process is water, wherein the refractive index of water is 1.4376.

[0087] Figure 9 The schematic diagram illustrates the light field intensity distribution within a second photoresist layer during surface plasmon interference exposure, as exemplified by this disclosure. The z-axis represents the thickness direction of the multilayer structure, and the x-axis represents the horizontal direction of the front view of the multilayer structure. Figure 9 Clear interference fringes can be observed, generated by the interference of surface plasmon waveguide modes propagating in opposite directions.

[0088] Figure 10 The diagram schematically illustrates the light field distribution curve at the center of the second photoresist layer, a specific example of this disclosure. Figure 10 The x-axis direction in the diagram is the horizontal direction of the front view of the multi-layer structure. From Figure 10 As can be seen, the interference fringes in the second photoresist layer have good uniformity, with an interference fringe period of 18.3 nm. The linewidth of the photolithography process is half of the interference fringe period, so the linewidth is 9.15 nm.

[0089] The embodiments of this disclosure can completely replace extreme ultraviolet (EUV) lithography with conventional deep ultraviolet (DUV) lithography to obtain ultra-narrow linewidths. In-situ fabrication of nanogratings using a self-aligned two-step exposure method significantly reduces the need for equipment modification and process complexity, while avoiding the introduction of impurities and the generation of grating defects. The nanogratings can diffract and couple deep ultraviolet incident light sources into surface plasmon waveguide modes, and the compression effect of these modes on the light field is used to fabricate ultra-narrow linewidth photoresist patterns. The embodiments of this disclosure can obtain photoresist patterns with linewidths less than 10 nm, broadening the application of deep ultraviolet lithography and meeting the current nanoscale linewidth requirements while significantly reducing the equipment and cost requirements of the lithography process.

[0090] Unless otherwise specified, the numerical parameters in this specification and the appended claims are approximate values ​​and can be changed according to the desired characteristics obtained from the content of this disclosure. Specifically, all figures used in the specification and claims to indicate the content of composition, reaction conditions, etc., should be understood to be modified by the term "about" in all cases. Generally, this means that there may be variations of ±10% in some embodiments, ±5% in some embodiments, ±1% in some embodiments, and ±0.5% in some embodiments.

[0091] Those skilled in the art will understand that the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in this disclosure. In particular, the features described in the various embodiments and / or claims of this disclosure can be combined or combined in various ways without departing from the spirit and teachings of this disclosure. All such combinations and / or combinations fall within the scope of this disclosure.

[0092] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A self-aligned deep ultraviolet lithography method, characterized in that, Includes the following steps: A multilayer structure is fabricated, wherein the multilayer structure includes: a substrate; a second metal layer disposed on the substrate; a second photoresist layer disposed on the side of the second metal layer away from the substrate; a first metal layer disposed on the side of the second photoresist layer away from the substrate; a hard mask layer disposed on the side of the first metal layer away from the substrate; and a first photoresist layer disposed on the side of the hard mask layer away from the substrate. A first photolithography process is performed on the first photoresist layer to obtain a first photoresist pattern; Using the first photoresist pattern as a mask, a nanograting is formed in the hard mask layer; and A second photolithography process is performed on the second photoresist layer using the nanograting to obtain a second photoresist pattern. Specifically, the step of performing a second photolithography process on the second photoresist layer using the nanograting to obtain a second photoresist pattern includes: The nanograting and surface plasmon waveguide are irradiated with incident light in the deep ultraviolet band, wherein the surface plasmon waveguide includes a first metal layer, a second photoresist layer and a second metal layer; The nanograting diffracts the incident light in the deep ultraviolet band to obtain a diffraction order; The diffraction order is excited in the surface plasmon waveguide to form a surface plasmon waveguide mode; The second photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode; and The second photoresist layer is developed to obtain a second photoresist pattern, wherein the linewidth of the second photoresist pattern is smaller than the linewidth of the first photoresist pattern.

2. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The diffraction order excited to form surface plasmonic waveguide modes in the surface plasmonic waveguide, including: A surface plasmonic waveguide mode is formed by exciting a higher-order diffraction order in the surface plasmonic waveguide, wherein the higher-order diffraction order includes diffraction orders greater than or equal to 3.

3. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The first photolithography process performed on the first photoresist layer to obtain the first photoresist pattern includes: The first photolithography process is performed on the first photoresist layer using incident light in the deep ultraviolet band to obtain the first photoresist pattern.

4. The self-aligned deep ultraviolet lithography method according to claim 1, characterized in that, The wavelength range of the incident light in the deep ultraviolet band includes 157 nm to 365 nm.

5. The self-aligned deep ultraviolet lithography method according to claim 1, characterized in that, The wavelength range of the incident light in the deep ultraviolet band includes 193nm to 266nm.

6. The self-aligned deep ultraviolet lithography method according to claim 3, wherein, The first photolithography process performed on the first photoresist layer using incident light in the deep ultraviolet band includes: An immersion lithography process is performed on the first photoresist layer using incident light with a wavelength of 193 nm.

7. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The second photolithography process performed on the second photoresist layer using the nanograting includes: Immersion lithography is performed on the second photoresist layer using the nanograting based on incident light with a wavelength of 193 nm.

8. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The materials of the second metal layer and the first metal layer are selected to be materials whose real part of dielectric constant is negative in the deep ultraviolet band.

9. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The nanograting is a one-dimensional periodic structure or a two-dimensional periodic structure.

10. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The period of the nanograting is equal to an integer multiple of the effective wavelength of the surface plasmon waveguide mode, and the integer is equal to the order of the diffraction order, which is an integer greater than or equal to 3.

11. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The period of the nanograting is less than or equal to 110 nm.

12. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The period of the nanograting is 40nm to 110nm.

13. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The nanograting has a duty cycle of 20%-80%, a thickness of 10-40 nm, and a thickness of 0-20 nm for the first metal layer.

14. The self-aligned deep ultraviolet lithography method according to claim 1, wherein, The thickness of the second photoresist layer is 10nm to 20nm.

15. The self-aligned deep ultraviolet lithography method according to claim 8, wherein, The thickness of the second photoresist layer is 10nm to 15nm.

16. The self-aligned deep ultraviolet lithography method according to any one of claims 1 to 15, wherein, The linewidth ratio of the second photoresist pattern to the linewidth of the first photoresist pattern is less than 1 / 10.

17. The self-aligned deep ultraviolet lithography method according to any one of claims 1 to 15, wherein, The second photoresist pattern includes patterns with a linewidth of less than or equal to 10 nm.

18. The self-aligned deep ultraviolet lithography method according to any one of claims 1 to 15, wherein, The second photoresist pattern includes a pattern with a linewidth of 7 to 10 nm.

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