Deep ultraviolet interferometric lithography method

Abstract

The present disclosure provides a deep ultraviolet interference lithography method, which can be applied to the field of semiconductor technology. The method comprises: preparing a multilayer structure, comprising: a substrate; a second metal layer arranged on the substrate; an isolation layer arranged on the side of the second metal layer away from the substrate; a photoresist layer arranged on the side of the isolation layer away from the substrate; a first metal layer arranged on the side of the photoresist layer away from the substrate; and a nanometer grating arranged on the side of the first metal layer away from the substrate. A lithography process is performed on the photoresist layer by using the nanometer grating to obtain a photoresist pattern; wherein the difference between the refractive index of the isolation layer and the photoresist layer is smaller than the difference between the refractive index of the isolation layer and the second metal layer.

Description

Technical Field

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

[0002] Photolithography is a crucial tool in chip manufacturing, and the minimum linewidth achievable by photolithography determines the precision of the chip structure. To achieve narrower linewidths in photolithography processes, extreme ultraviolet (EUV) light sources are required. However, EUV photolithography is challenging, faces numerous bottlenecks, and is subject to severe technological embargoes.

[0003] Interference exposure technology can be used to generate narrow-linewidth periodic structures in photoresist. The principle is to use the interference fringes generated by two incident beams with different propagation directions to interfere with the photoresist, thereby obtaining a periodic structure in the photoresist. The linewidth is about half the period of the periodic structure. In free space, the linewidth is limited by the optical diffraction limit. In order to overcome this limitation, researchers have proposed a technique to achieve interference exposure using the surface plasmon effect. Surface plasmon is an electromagnetic wave that propagates along the surface. During the propagation process, the light field is confined to the surface. Since the propagation constant of surface plasmon is greater than the wave vector in free space, the surface plasmon modes propagating in opposite directions can generate interference fringes with shorter periods. In 2004, Luo, XG and T. Ishihara first proposed a photolithography method based on the surface plasmon resonance effect to achieve subwavelength size. Theoretically, a spatial resolution of 50 nm can be achieved based on visible light or ultraviolet light sources [Luo, XG and T. Ishihara, Optics Express, 2004. 12(14): p. 3055-3065.]. To further compress the period of interference fringes, shorter wavelength incident light sources and / or increased propagation constants of surface plasmons can be used to achieve smaller period interference fringes. However, this method still has theoretical limitations. Specifically, when the incident light wavelength remains constant, the contrast of the interference fringes on the photoresist layer surface decreases significantly as the interference exposure linewidth decreases. This effect limits the linewidth processing capability of deep ultraviolet interference lithography. Given the current challenges, bottlenecks, and severe technological blockades in extreme ultraviolet lithography, improving the linewidth processing capability of deep ultraviolet interference lithography is of great significance for breaking through technological monopolies and blockades and promoting the development of the microelectronics industry. Summary of the Invention

[0004] In view of this, embodiments of the present disclosure provide a deep ultraviolet interference lithography method, which can effectively alleviate the problem of decreased interference fringe contrast caused by reduced linewidth of interference exposure without changing the incident light wavelength, and improve the quality of photoresist pattern while obtaining ultra-narrow linewidth photoresist pattern.

[0005] One aspect of this disclosure provides a deep ultraviolet interference lithography method, comprising: fabricating a multilayer structure, wherein the multilayer structure includes: a substrate; a second metal layer disposed on the substrate; an isolation layer disposed on the second metal layer away from the substrate; a photoresist layer disposed on the isolation layer away from the substrate; a first metal layer disposed on the photoresist layer away from the substrate; and a nanograting disposed on the first metal layer away from the substrate; performing a photolithography process on the photoresist layer using the nanograting to obtain a photoresist pattern; wherein the refractive index difference between the isolation layer and the photoresist layer is less than the refractive index difference between the isolation layer and the second metal layer. The difference lies in the method of performing photolithography on the photoresist layer using the nanograting to obtain a photoresist pattern, specifically including: 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, the photoresist layer, the isolation 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 photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode; and the photoresist layer is developed to obtain a photoresist pattern.

[0006] According to embodiments of this disclosure, the isolation layer is made of an optical medium material with the same refractive index as the photoresist layer; the isolation layer is not photosensitive after exposure by the surface plasmon interference.

[0007] According to embodiments of this disclosure, the photoresist layer has anisotropic exposure characteristics, wherein the anisotropic exposure characteristics include sensitivity to electric field components in a specific direction only in the light field; the specific direction includes the thickness direction of the multilayer structure.

[0008] According to embodiments of this disclosure, the wavelength range of the incident light in the deep ultraviolet band includes 157 nm to 365 nm.

[0009] According to embodiments of this disclosure, the wavelength range of the incident light in the deep ultraviolet band includes 193 nm to 266 nm.

[0010] According to embodiments of this disclosure, an immersion lithography process is performed on the photoresist layer using the nanograting based on incident light with a wavelength of 193 nm.

[0011] According to embodiments of this disclosure, the materials of the first metal layer and the second metal layer are selected to be materials whose real part of dielectric constant is negative in the deep ultraviolet band.

[0012] According to embodiments of this disclosure, the material of the first metal layer includes at least one of gold, silver, aluminum, and magnesium-aluminum alloy, and / or the material of the second metal layer includes at least one of gold, silver, aluminum, and magnesium-aluminum alloy.

[0013] According to embodiments of this disclosure, the nanograting is a one-dimensional periodic structure or a two-dimensional periodic structure.

[0014] According to embodiments of this disclosure, the thickness of the photoresist layer is 5-20 nm, and / or the thickness of the isolation layer is 5-20 nm.

[0015] According to embodiments of this disclosure, the sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–20 nm.

[0016] According to embodiments of this disclosure, the sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–15 nm.

[0017] According to embodiments of this disclosure, the period of the nanograting is 50-110 nm, the thickness of the nanograting is 10-40 nm, and the duty cycle of the nanograting is 20%-80%.

[0018] According to embodiments of this disclosure, the linewidth of the photoresist pattern is less than or equal to 10 nm.

[0019] According to embodiments of this disclosure, the linewidth of the photoresist pattern is 7-10 nm.

[0020] The ultra-narrow linewidth deep ultraviolet lithography process provided by the embodiments of this disclosure, at least by introducing an isolation layer, avoids the problem that the contrast of interference fringes near the lower surface of the photoresist layer close to the second metal layer decreases as the linewidth decreases due to direct contact between the photoresist layer and the second metal layer, thereby improving the quality of the photoresist pattern and thus enhancing the linewidth processing capability of deep ultraviolet lithography. Attached Figure Description

[0021] 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:

[0022] Figure 1 This is a flowchart of a deep ultraviolet interference lithography method according to an embodiment of the present disclosure.

[0023] Figure 2The flowchart illustrates a method for performing a photolithography process on a photoresist layer using a nanograting to obtain a photoresist pattern in a deep ultraviolet interference lithography method according to an embodiment of the present disclosure.

[0024] Figure 3 A schematic front view of a multilayer structure for a deep ultraviolet interference lithography method according to an embodiment of the present disclosure is shown.

[0025] Figure 4 The diagram schematically shows a front view of a multilayer structure illuminated by incident light in the deep ultraviolet band.

[0026] Figure 5 A schematic front view of the multilayer structure with the nanograting and the first metal layer stripped off is shown.

[0027] Figure 6 The diagram schematically shows a front view of a multilayer structure after the photoresist layer has been developed.

[0028] Figure 7 The light field |E| inside a multilayer structure in deep ultraviolet interference lithography, as illustrated in the example of this disclosure, is schematically shown. 2 Intensity distribution map.

[0029] Figure 8 The schematic illustration shows the internal optical field |E| of the photoresist in an example surface plasmon waveguide of this disclosure. 2 Intensity distribution map.

[0030] Figure 9a The schematic illustration shows the internal optical field |E of the photoresist in an example surface plasmon waveguide of this disclosure. x | 2 Intensity component distribution diagram.

[0031] Figure 9b The schematic illustration shows the internal optical field |E of the photoresist in an example surface plasmon waveguide of this disclosure. z | 2 Intensity component distribution diagram.

[0032] Figure reference numerals: 1-substrate; 2-second metal layer; 3-isolation layer; 4-photoresist layer; 5-first metal layer; 6-nano grating; 7-incident light; 8-photoresist pattern. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In this document, unless otherwise specified, "deep ultraviolet" refers to ultraviolet light with a wavelength range of 157–365 nm; "extreme ultraviolet" refers to ultraviolet light with a wavelength range of 10–121 nm.

[0038] Photolithography is a crucial tool in chip manufacturing, and the minimum linewidth achievable through photolithography determines the precision of the chip structure. 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 more circuit units to be integrated onto the same area.

[0039] In free space, linewidth is limited by the optical diffraction limit. To achieve narrower linewidths in photolithography, extreme ultraviolet (EUV) light sources are required, but EUV technology is highly complex. Research has found that using surface plasmon resonance (SPR) to achieve interferometric exposure can generate shorter-period interference fringes, thereby further reducing linewidth. SPR utilizes SPR to achieve interferometric exposure. SPR is an electromagnetic wave mode that propagates along a surface due to the interaction between light and free electrons on a metal surface. By utilizing the mutual interference between SPRs, a light field grating with a period shorter than that of the metal grating can be formed in the photoresist, thus overcoming the diffraction limit. To further compress the period of the interference fringes, shorter wavelength deep ultraviolet incident light and SPR waveguides can be used. SPR waveguides can guide the directional propagation of SPRs and can support SPR modes with larger propagation constants, thereby achieving interference fringes with smaller periods. However, this method still has theoretical limitations. Specifically, when the incident light wavelength remains constant, the contrast of the interference fringes on the photoresist layer surface decreases significantly as the interference exposure linewidth decreases. Reducing the impact of this effect on the processing capability of deep ultraviolet interference lithography is of great significance to the development of lithography technology, given the current challenges, bottlenecks, and severe technological blockades in extreme ultraviolet lithography.

[0040] In one exemplary embodiment of this disclosure, a deep ultraviolet interference lithography method is provided.

[0041] Figure 1 This is a flowchart of a deep ultraviolet interference lithography method according to an embodiment of the present disclosure.

[0042] like Figure 1 As shown, the self-aligned deep ultraviolet lithography process of this embodiment includes operations S101 to S102.

[0043] In operation S101, a multilayer structure is fabricated. The multilayer structure includes: a substrate; a second metal layer disposed on the substrate; an isolation layer disposed on the side of the second metal layer away from the substrate; a photoresist layer disposed on the side of the isolation layer away from the substrate; a first metal layer disposed on the side of the photoresist layer away from the substrate; and a nanograting disposed on the side of the first metal layer away from the substrate.

[0044] In operation S102, the photolithography process is performed on the photoresist layer using the nanograting to obtain a photoresist pattern.

[0045] In the embodiments of this disclosure, the difference in refractive index between the isolation layer and the photoresist layer is smaller than the difference in refractive index between the isolation layer and the second metal layer. When performing photolithography on the photoresist layer using a nanograting, there is a significant difference in refractive index between the photoresist layer and the second metal layer. When the photoresist layer is in direct contact with the second metal layer, the difference in refractive index causes the contrast of the interference fringes near the lower surface of the photoresist layer close to the second metal layer to decrease as the linewidth decreases, resulting in a decrease in the quality of the processed photoresist pattern. By introducing an isolation layer with a smaller refractive index difference compared to the second metal layer and the photoresist layer, the contrast of the interference fringes near the lower surface of the photoresist layer close to the second metal layer can be improved, thereby enhancing the processing capability of subsequent processes and obtaining a higher quality photoresist pattern.

[0046] The photolithography process of operating S102 also includes the step of using a nanograting to diffract 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 photoresist layer.

[0047] Figure 2 The flowchart illustrates a method for performing a photolithography process on a photoresist layer using a nanograting to obtain a photoresist pattern in a deep ultraviolet interference lithography method according to an embodiment of the present disclosure.

[0048] like Figure 2 As shown, the method S102 of this embodiment for performing photolithography on a photoresist layer using a nanograting to obtain a photoresist pattern further includes operations S1021 to S1025.

[0049] In operation S1021, 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 photoresist layer and the second metal layer.

[0050] In operation S1022, the nanograting diffracts the incident light in the deep ultraviolet band to obtain a diffraction order.

[0051] In operation S1023, the diffraction stage is excited in the surface plasmon waveguide to form a surface plasmon waveguide mode.

[0052] In operation S1024, the photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode.

[0053] In operation S1025, the photoresist layer is developed to obtain a photoresist pattern.

[0054] Figure 3 A schematic front view of a multilayer structure for a deep ultraviolet interference lithography method according to an embodiment of the present disclosure is shown.

[0055] exist Figure 3 The multilayer structure used in deep ultraviolet interference lithography includes a substrate 1, a second metal layer 2, an isolation layer 3, a photoresist layer 4, a first metal layer 5, and a nanograting 6. 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, an isolation layer 3 can be prepared on the surface of the second metal layer 2. Then, a photoresist layer 4 is prepared on the surface of the isolation layer 3 using a spin-coating method. A metal thin film is prepared again using electron beam evaporation to obtain a first metal layer 5 close to the photoresist layer 4. A nanograting 6 can be further prepared on the first metal layer 5 to complete the fabrication of the multilayer structure. It should be understood that the multilayer structure is used to prepare ultra-narrow linewidth photoresist patterns, and each layer is nanoscale.

[0056] 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 photoresist layer, and a second metal layer. The first metal layer and the photoresist layer have opposite dielectric constants, as do the second metal layer. 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, they can significantly change and modulate the wave vector of the surface plasmon polaritons, thereby forming opposing propagating surface plasmon waveguide modes, and using these modes to form interference fringes in the 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 photoresist patterns with ultra-narrow linewidth.

[0057] In some embodiments, the isolation layer is made of an optical medium material with the same refractive index as the photoresist layer. Furthermore, the optical properties of the isolation layer remain unchanged after surface plasmon interference exposure; for example, the isolation layer becomes non-photosensitive after surface plasmon interference exposure. This further improves the contrast of interference fringes near the lower surface of the photoresist layer on the side close to the second metal layer, resulting in a high-quality photoresist pattern. A typical example is that the isolation layer can be made of the same type of photoresist material as the photoresist layer, the difference being that the photoresist layer material is photosensitive while the isolation layer material has lost its photosensitive activity; for example, the isolation layer material can be a degraded photoresist. Another typical example is that the isolation layer material can be another type of non-photosensitive material with the same refractive index as the photoresist layer material, such as silicon nitride (SiN).

[0058] According to embodiments of this disclosure, the deep ultraviolet interference 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. Preferably, the wavelength range of the incident light in the deep ultraviolet band includes 193 nm to 266 nm. In some specific embodiments, the wavelength of the incident light in the deep ultraviolet band can be common light sources such as 193 nm or 266 nm.

[0059] According to embodiments of this disclosure, performing a photolithography process on the photoresist layer using the nanograting includes: performing an immersion photolithography process on the photoresist layer using the nanograting based on incident light with a wavelength of 193 nm. During the photolithography process, an immersion layer can 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.

[0060] In some embodiments, the photoresist layer exhibits anisotropic exposure characteristics, wherein the anisotropic exposure characteristics include sensitivity only to the electric field component in a specific direction of the light field. Photoresist is a photosensitive liquid mixture, typically composed of a photoinitiator (photosensitizer, photoacid generator), photoresist resin, solvent, monomer (reactive diluent), and other additives. In the photolithography process, the photoresist is applied to a substrate. After light or radiation passes through a mask and irradiates the substrate, the solubility of the photoresist in the developing solution changes. After the soluble portion is dissolved by the solution, the photoresist layer forms a pattern identical to that on the mask, which is then etched onto the substrate to complete the pattern transfer. Based on the presence or absence of electric or magnetic field components in the propagation direction, light can be classified into TEM waves (no electric or magnetic field components in the propagation direction, called transverse electromagnetic waves), TE waves (a magnetic field component but no electric field component in the propagation direction, called transverse electric waves, i.e., s-waves), and TM waves (an electric field component but no magnetic field component in the propagation direction, called transverse magnetic waves, i.e., p-waves). In the embodiments of this disclosure, since the periodic structure of the nanograting lacks symmetry, the diffracted wave is a TM wave. During exposure, the local field in the photoresist layer contains Ex and Ez components. The combined effect of the Ex and Ez components may cause a decrease in the contrast of the interference fringes. Embodiments of this disclosure have found that a photoresist layer with anisotropic exposure characteristics can be sensitive only to the electric field component in a specific direction of the light field, for example, only to the Ez component along the thickness direction of the multilayer structure, thereby helping to improve the quality of the periodic pattern formed after interference exposure of the photoresist layer. For example, the interior of the photoresist layer may contain chain-like macromolecular structures and / or metal nanorod structures, wherein the metal nanorods can be noble metal nanorods. The introduction of chain-like macromolecular structures or metal nanorod structures makes the photoresist layer sensitive only to the electric field component in a specific direction, thereby improving the quality of the photoresist pattern from the exposure mechanism of the photoresist and obtaining high-quality ultra-narrow linewidth photoresist patterns.

[0061] In some embodiments, the nanograting is a one-dimensional periodic structure or a two-dimensional periodic structure.

[0062] In some embodiments, the materials of the first metal layer and the second metal layer are selected to have a negative real part of the dielectric constant in the deep ultraviolet band, in order to generate surface plasmon resonances. Preferably, the material of the first metal layer includes at least one of gold, silver, aluminum, magnesium, and magnesium-aluminum alloys, and / or the material of the second metal layer includes at least one of gold, silver, aluminum, magnesium, and magnesium-aluminum alloys.

[0063] Furthermore, the structural parameters of the nanograting and the surface plasmon waveguide (SPL) can be optimized to improve the excitation efficiency of the SPL mode and obtain an ultra-narrow linewidth photoresist pattern. For example, the period, thickness, and duty cycle of the nanograting can be optimized to efficiently couple the SPL mode. The specific selection of these structural parameters can be adjusted according to the incident light wavelength. Preferably, the period of the nanograting is 50–110 nm; the thickness of the nanograting is 10–40 nm; and the duty cycle of the nanograting is 20%–80%. Further, the thickness of the photoresist layer and / or the thickness of the isolation layer can also be optimized to obtain an ultra-narrow linewidth. For example, the thickness of the photoresist layer is 5–20 nm, and / or the thickness of the isolation layer is 5–20 nm. Preferably, the sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–20 nm. More preferably, the sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–15 nm.

[0064] According to embodiments of this disclosure, the linewidth of the obtained photoresist pattern can be less than or equal to 10 nm.

[0065] More preferably, by optimizing the structural parameters of the nanograting and the surface plasmon waveguide, a photoresist pattern with a linewidth of 7–10 nm can be obtained.

[0066] The following is combined Figures 4 to 9b This disclosure describes in detail a specific example of a deep ultraviolet interference lithography method. It should be understood that the following description is merely illustrative and not a specific limitation of this disclosure.

[0067] The specific example of the deep ultraviolet interference lithography method disclosed herein includes steps S1 to S3.

[0068] Step S1: Fabrication of a multilayer structure. A single-crystal silicon substrate is selected as the substrate. A 30nm aluminum, magnesium, or magnesium-aluminum alloy thin film is prepared using electron beam evaporation as the lower second metal layer 2. Then, a 5nm thick isolation layer 3 is prepared on the surface of the second metal layer 2 using spin coating. Further, a 10nm thick photoresist layer 4 is prepared on the surface of the isolation layer 3 using spin coating. Again, a 30nm metal thin film is prepared using electron beam evaporation as the first metal layer 5. A nanograting 6 is then prepared on the first metal layer 5 to complete the fabrication of the multilayer structure. The isolation layer 3 and the photoresist layer 4 are made of the same material, but the material of the isolation layer 3 has lost its photosensitive activity, while the material of the photoresist layer 4 has photosensitive activity.

[0069] Step S2: Irradiate the multilayer structure containing the nanograting 6 using an immersion deep ultraviolet lithography process with a wavelength of 193nm. The generated diffraction order is coupled into a surface plasmonic waveguide mode that propagates in opposite directions in the surface plasmonic waveguide, which can form interference fringes in the photoresist layer 4, thus completing the surface plasmonic interference exposure.

[0070] Figure 4 The diagram schematically illustrates a front view of a multilayer structure illuminated by incident light in the deep ultraviolet band. The multilayer structure includes a substrate 1, a second metal layer 2, an isolation layer 3, a photoresist layer 4, a first metal layer 5, and a nanograting 6. When the multilayer structure is illuminated perpendicularly by incident light 7, the nanograting 6 diffracts the incident light 7, generating diffraction orders and exciting counter-propagating surface plasmon waveguide modes, forming interference fringes in the photoresist layer 4.

[0071] Further, in step S3, the nanograting 6 and the first metal layer 4 are peeled off using a stripping process, leaving the photoresist layer 3. In step S4, the photoresist layer 3 is developed to obtain a photoresist pattern 8, wherein the linewidth of the photoresist pattern 8 is approximately equal to half the period of the interference fringe generated in the photoresist layer 3. In a specific example of this disclosure, the interference fringe period is 14 nm, thereby obtaining a photoresist pattern 8 with a linewidth of 7 nm.

[0072] Figure 5 A schematic front view of a multilayer structure with the nanograting and first metal layer stripped away is shown. Figure 5 In the middle, the multilayer structure with the nanograting 6 and the first metal layer 5 stripped off includes a substrate 1, a second metal layer 2, an isolation layer 3, and a photoresist layer 4.

[0073] Figure 6 A schematic diagram shows a front view of a multilayer structure after photoresist layer development. Figure 6 In the process, the multilayer structure after developing the photoresist layer includes a substrate 1, a second metal layer 2, an isolation layer 3, and a photoresist pattern 8. It should be understood that the photoresist pattern 8 is the remaining portion after developing the photoresist layer 4. Further, the pattern in the photoresist pattern 8 can be transferred to the isolation layer 3 by etching, and then to the second metal layer 2, and further transferred to the substrate 1 by etching, which serves as a metal mask.

[0074] To verify the feasibility of the deep ultraviolet interference 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 isolation layer refractive index is 1.7, the dielectric constants of the first metal layer 5 and the second metal layer 2 are both −3.33, and the immersion layer material of the immersion deep ultraviolet lithography process is water, wherein the refractive index of water is 1.4376.

[0075] Figure 7 The light field |E| inside a multilayer structure in deep ultraviolet interference lithography, as illustrated in the example of this disclosure, is schematically shown. 2 Intensity distribution diagram. The z-axis represents the thickness direction of the multi-layer structure, and the x-axis represents the horizontal direction of the front view of the multi-layer structure. From... Figure 7 As can be seen, photoresist layer 3 exhibits obvious interference fringes generated by the interference of counter-propagating surface plasmon waveguide modes. The period of these interference fringes is 14 nm, and the linewidth of the photolithography process is half the period of the interference fringes, therefore the linewidth is 7 nm. However, from... Figure 7 It can be observed that the interference fringes have high contrast only in the central region of the surface plasmon waveguide.

[0076] Figure 8 The schematic illustration shows the internal optical field |E| of the photoresist in an example surface plasmon waveguide of this disclosure. 2 Intensity distribution diagram. The z-axis represents the thickness direction of the multi-layer structure, and the x-axis represents the horizontal direction of the front view of the multi-layer structure. From... Figure 8 As can be seen, the introduction of the isolation layer 3 significantly improves the contrast of the interference fringes near the interface between the photoresist layer 4 and the second metal layer 2. However, the disappearance of the interference fringes near the interface between the photoresist layer 4 and the first metal layer 5 results in a photoresist pattern thickness of approximately 5 nm after exposure.

[0077] Figure 9a The schematic illustration shows the internal optical field |E of the photoresist in an example surface plasmon waveguide of this disclosure. x | 2 Intensity component distribution diagram. Figure 9b The schematic illustration shows the internal optical field |E of the photoresist in an example surface plasmon waveguide of this disclosure. z | 2 Intensity component distribution map. Among them, Figure 9a and Figure 9b In the diagram, the z-axis represents the thickness direction of the multi-layer structure, and the x-axis represents the horizontal direction of the front view of the multi-layer structure. By comparison... Figure 9a and Figure 9b Mid-field | E x | 2 Intensity components and light field |Ez | 2 The enhanced regions of the intensity components reveal a separation in their distribution along the x-direction. Light field |E| 2 Intensity can be expressed as the light field |E x | 2 Intensity components and light field |E z | 2 The summation of intensity components, i.e., |E| 2 =|E x | 2 +|E z | 2 Therefore, it can be concluded that the decrease in contrast of the interference fringes is due to the light field |E x | 2 Intensity components and light field |E z | 2 The intensity components interact during the interference exposure process. When photoresist layer 4 uses a photoresist with anisotropic exposure characteristics that is sensitive only to the electric field component in the z-direction of the light field, the exposed pattern is only affected by the light field |E|. z | 2 Intensity component correlation. From Figure 9b As can be seen, using a photoresist layer with anisotropic exposure characteristics helps improve the quality of the photoresist pattern of the periodic structure formed after interference exposure. The contrast of the interference fringes near the interface between the photoresist layer 4 and the first metal layer 5 is significantly enhanced, and the photoresist pattern thickness is increased to 10 nm, thus improving the processing capability of the deep ultraviolet interference lithography method of this disclosure example.

[0078] The embodiments of this disclosure, by introducing an isolation layer, avoid the problem of decreased contrast of interference fringes near the lower surface of the photoresist layer close to the second metal layer due to direct contact between the photoresist layer and the second metal layer, thus improving the quality of the photoresist pattern. Furthermore, by using a photoresist layer with anisotropic exposure characteristics, the quality of the periodic structure photoresist pattern formed after interference exposure is improved, thereby enhancing the processing capability of the deep ultraviolet interference lithography method. The embodiments of this disclosure can obtain high-quality photoresist patterns with linewidths less than 10 nm, broadening the application of deep ultraviolet lithography and meeting the current nanoscale linewidth process requirements while significantly reducing the technical, equipment, and cost requirements of extreme ultraviolet lithography.

[0079] 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 a variation of ±10% in some embodiments, ±5% in some embodiments, ±1% in some embodiments, and ±0.5% in some embodiments.

[0080] 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.

[0081] 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 deep ultraviolet interference lithography method, characterized in that, include: A multilayer structure is fabricated, wherein the multilayer structure includes: a substrate; a second metal layer disposed on the substrate; an isolation layer disposed on the second metal layer away from the substrate; a photoresist layer disposed on the isolation layer away from the substrate; a first metal layer disposed on the photoresist layer away from the substrate; and a nanograting disposed on the first metal layer away from the substrate. The photoresist layer is subjected to a photolithography process using the nanograting to obtain a photoresist pattern; Wherein, the refractive index difference between the isolation layer and the photoresist layer is smaller than the refractive index difference between the isolation layer and the second metal layer; Specifically, the step of performing a photolithography process on the photoresist layer using the nanograting to obtain a 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 photoresist layer, an isolation 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 photoresist layer is subjected to surface plasmon interference exposure based on the surface plasmon waveguide mode. The photoresist layer is developed to obtain a photoresist pattern.

2. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The isolation layer is made of an optical medium material with the same refractive index as the photoresist layer; the isolation layer is not photosensitive after exposure to surface plasmon interference.

3. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The photoresist layer has anisotropic exposure characteristics, wherein the anisotropic exposure characteristics include sensitivity to electric field components only in a specific direction in the light field, and the specific direction includes the thickness direction of the multilayer structure.

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

7. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The materials of the first metal layer and the second metal layer are selected to have a negative real part of the dielectric constant in the deep ultraviolet band.

8. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The material of the first metal layer includes at least one of gold, silver, aluminum, and magnesium-aluminum alloy, and / or the material of the second metal layer includes at least one of gold, silver, aluminum, and magnesium-aluminum alloy.

9. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The nanograting is a one-dimensional periodic structure or a two-dimensional periodic structure.

10. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The thickness of the photoresist layer is 5-20 nm, and / or the thickness of the isolation layer is 5-20 nm.

11. The deep ultraviolet interference lithography method according to claim 10, characterized in that, The sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–20 nm.

12. The deep ultraviolet interference lithography method according to claim 11, characterized in that, The sum of the thickness of the photoresist layer and the thickness of the isolation layer is 10–15 nm.

13. The deep ultraviolet interference lithography method according to claim 1, characterized in that, The period of the nanograting is 50-110 nm, the thickness of the nanograting is 10-40 nm, and the duty cycle of the nanograting is 20%-80%.

14. The deep ultraviolet interference lithography method according to any one of claims 1 to 13, characterized in that, The linewidth of the photoresist pattern is less than or equal to 10 nm.

15. The deep ultraviolet interference lithography method according to claim 14, characterized in that, The linewidth of the photoresist pattern is 7–10 nm.

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