Super-resolution photoetching method combined with local photothermal effect and application of super-resolution photoetching method
By combining a super-resolution lithography method with localized photothermal effects, nanoscale patterns are formed in the photoresist layer using photothermal reactions. This solves the problem of limited resolution in lithography technology, achieves higher resolution and more stable lithography results, and reduces equipment costs.
Patent Information
- Application Number
- CN202511419249.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-30
- Publication Date
- 2025-11-11
AI Technical Summary
Existing photolithography technology is limited by the optical diffraction limit, making it difficult to achieve higher resolutions. Furthermore, traditional super-resolution photolithography technology has stringent requirements for light sources and photoresist materials, resulting in artifacts and uneven linewidth.
The super-resolution lithography method combining local photothermal effect introduces photoresist with specific cross-linking properties and an optimized illumination source into the photoresist layer. It utilizes photothermal reaction to form nanoscale patterns, and employs a superlens film structure to convert light energy into heat energy, controlling the local temperature rise of the photoresist to achieve the cross-linking reaction.
It significantly improves the resolution of super-resolution lithography, suppresses artifacts and linewidth inhomogeneity, reduces the requirements for light source stability and spectral width, broadens the application range of light sources, reduces equipment costs, and improves process stability and compatibility.
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Figure CN120928658A_ABST
Abstract
Description
Technical Field
[0001] This disclosure relates to the fields of micro-nano fabrication and advanced photolithography, and in particular to a super-resolution photolithography method that combines local photothermal effects and its applications. Background Technology
[0002] Photolithography is a core process in microelectronics manufacturing and nanofabrication, and its resolution directly determines the integration density and performance of integrated circuits. Traditional optical projection lithography improves resolution by shortening the wavelength of the exposure light source and increasing the numerical aperture of the projection lens. However, limited by the optical diffraction limit, its resolution is difficult to break through the physical limitation of half a wavelength. Currently, extreme ultraviolet (EUV) lithography utilizes a short-wavelength light source of 13.5 nm, achieving a resolution below ten nanometers. However, this system is extremely expensive and places extremely stringent requirements on the materials and processes of the light source, mask, and photoresist.
[0003] To overcome the diffraction limit, researchers have proposed various super-resolution lithography techniques. Among them, super-resolution lithography based on surface plasmon polaritons (SPPs) or other surface electromagnetic modes shows great potential. This type of technique utilizes metals or dielectric materials with negative permittivity in the deep ultraviolet to visible light range to construct superlens structures. By exciting and modulating surface electromagnetic modes, the light field energy is localized within the nanoscale range, thereby achieving lithographic patterns that exceed the traditional diffraction limit. However, these techniques are still limited by the near-field diffraction limit, and further improvements in resolution face significant challenges. Furthermore, these methods typically rely heavily on the photochemical reactions of the photoresist, placing high demands on the coherence, power stability, and wavelength of the light source, and are prone to artifacts and linewidth inhomogeneities due to sidelobe effects. Summary of the Invention
[0004] (a) Technical problems to be solved
[0005] To address at least one of the aforementioned technical problems in the prior art, embodiments of this disclosure provide a super-resolution lithography method incorporating localized photothermal effects and its applications. By introducing localized photothermal effects into super-resolution lithography based on surface plasmon resonances or other surface electromagnetic modes, and employing a photoresist with specific cross-linking properties and an optimized illumination source, a patterning process is induced in the photoresist that is primarily photothermal rather than a traditional photochemical reaction. This method achieves higher resolution than traditional photochemical reactions through a photothermal mechanism, significantly enhancing the ultimate resolution capability of super-resolution lithography. It can be applied to super-resolution lithography fields such as direct-write lithography, interference lithography, and imaging lithography.
[0006] (II) Technical Solution
[0007] To address the aforementioned technical problems, embodiments of this disclosure propose a super-resolution lithography method incorporating localized photothermal effects and its applications.
[0008] According to a first aspect of this disclosure, a super-resolution lithography method incorporating localized photothermal effects is provided, comprising: fabricating a superlens film structure comprising a photoresist layer and at least one metal layer on a substrate, the photoresist layer comprising a photoresist having thermal crosslinking reaction characteristics; providing a mask having a nano-diffraction structure configured to cooperate with the superlens film structure to excite surface plasmon electromagnetic modes; bringing the mask close to the substrate, irradiating the mask with an illumination source to excite the surface plasmon electromagnetic modes and form a nanoscale localized enhanced light field in the photoresist layer; converting the energy of the localized enhanced light field into heat energy through the absorption of light energy by the superlens film structure, generating a spatially confined localized temperature rise in the photoresist layer; controlling the irradiation parameters of the illumination source so that the temperature of the photoresist region with the localized temperature rise in the photoresist layer exceeds a thermal response threshold and undergoes a crosslinking or curing reaction; developing the photoresist layer to remove photoresist regions that have not undergone crosslinking or curing reactions, forming a super-resolution nanopattern.
[0009] In some exemplary embodiments, the photoresist with thermal crosslinking reaction properties has a thermal response threshold, a low light absorption coefficient, and a low thermal diffusivity. The photoresist with thermal crosslinking reaction properties has a light absorption coefficient of less than 1.2 × 10⁻⁶ in the illumination source wavelength range. 5 m -1 The thermal diffusivity is less than 0.2 W / (m·K).
[0010] In some exemplary embodiments, the superlens film structure includes, but is not limited to, one of the following structures: a metal transmission layer, a photoresist layer, a metal reflection layer and a substrate; a metal transmission layer, a photoresist layer and a substrate; or a photoresist layer, a metal reflection layer and a substrate.
[0011] In some exemplary embodiments, a method for fabricating a superlens film structure comprising a photoresist layer and at least one metal layer on a substrate includes, in response to the superlens film structure comprising a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate, the method comprising: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; spin-coating a photoresist having thermal crosslinking reaction properties onto the metal reflection layer to form a photoresist layer; forming a metal transmission layer on the photoresist layer by physical vapor deposition or chemical vapor deposition; or in response to the superlens film structure comprising a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate, the method comprising: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; or, in response to the superlens film structure comprising a metal transmission layer, a photoresist layer, a metal reflection layer, and a metal reflection layer, the method comprising: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; or, in response to the superlens film structure comprising a metal transmission layer, a metal reflection ... and a metal reflection layer, the method comprising: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; or, in response to the superlens film structure comprising a metal transmission layer, a metal reflection layer, and a metal reflection layer, the method comprising: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; or, in response The lens film structure includes a metal transmission layer, a photoresist layer, and a substrate. The method includes: spin-coating a photoresist with thermal cross-linking properties onto the substrate surface to form a photoresist layer; forming a metal transmission layer on the photoresist layer using physical vapor deposition or chemical vapor deposition. Alternatively, in response to a superlens film structure including a photoresist layer, a metal reflection layer, and a substrate, the method includes: forming a metal reflection layer on the substrate surface using physical vapor deposition or chemical vapor deposition; spin-coating a photoresist with thermal cross-linking properties onto the metal reflection layer to form a photoresist layer.
[0012] In some exemplary embodiments, the mask with a nanodiffraction structure includes a substrate and an absorption layer with a nanodiffraction structure, the absorption layer with a nanodiffraction structure being prepared on the surface of the substrate by deposition and etching processes.
[0013] In some exemplary embodiments, before preparing the absorption layer with the nanodiffraction structure on the substrate surface by deposition and etching processes, the method further includes: optimizing the geometric parameters of the nanodiffraction structure by employing at least one modulation method selected from non-uniform periodic modulation, width modulation, and Gaussian modulation.
[0014] In some exemplary embodiments, the nanodiffraction structure includes one of a one-dimensional grating, a two-dimensional grating, a two-dimensional nanoarray, a nanoantenna, a spiral groove, and a radially symmetric structure.
[0015] In some exemplary embodiments, illuminating the mask with an illumination source includes: selecting at least one of a continuous wave source or a pulsed source with a wavelength in the deep ultraviolet, ultraviolet, visible, or near-infrared bands as the illumination source; adjusting the polarization state of the illumination source to match the symmetry of the nano-diffraction structure to excite the surface plasmon electromagnetic modes of the nano-diffraction structure; and controlling the power density of the illumination source within 10... 3 The illumination intensity is in the range of W / cm² or higher, and the illumination time is on the order of nanoseconds to milliseconds; wherein, the polarization mode of the illumination source includes at least one of unpolarized, linearly polarized and circularly polarized.
[0016] In some exemplary embodiments, the energy of the locally enhanced light field is converted into heat energy by absorbing light energy through the superlens film structure. This includes: generating a spatially localized heating source in the photoresist by exciting the locally enhanced light power based on the superlens film structure, thereby achieving nanoscale heating control in the photoresist; and confining the heat energy within the range of the locally enhanced light field based on the low thermal diffusivity of the photoresist, thereby forming a temperature rise distribution with a lateral feature size of less than 100 nanometers.
[0017] In some exemplary embodiments, controlling the irradiation parameters of the illumination source to cause the temperature of the photoresist region in the photoresist layer to exceed the thermal response threshold and undergo crosslinking or curing reactions includes: determining the power density and irradiation time of the illumination source based on the thermal response threshold and thermal diffusion characteristics of the photoresist; monitoring the temperature distribution in the photoresist layer in real time to dynamically adjust the power density and irradiation time of the illumination source in real time, controlling the temperature rise amplitude and spatial distribution in the photoresist layer, so that the temperature of the target area exceeds the thermal response threshold and the temperature of the non-target area is lower than the thermal response threshold, wherein the thermal response threshold is the glass transition temperature or thermal crosslinking temperature of the photoresist.
[0018] According to a second aspect of this disclosure, an application of the above-described super-resolution lithography method incorporating local photothermal effects is provided, which is used in direct-write lithography, interference lithography, or projection lithography.
[0019] (III) Beneficial Effects
[0020] As can be seen from the above technical solutions, the super-resolution lithography method and its application that combines local photothermal effects provided by the embodiments of this disclosure have at least the following beneficial effects:
[0021] (1) By introducing a local photothermal effect, a secondary compression of the exposure area by thermal field is achieved on the basis of focusing the nanoscale light field excited by surface electromagnetic modes such as surface plasmons. The photothermal effect forms a spatially confined temperature rise distribution at the focal spot of the light field, which is equivalent to adding a thermal shrinkage window, and can further compress the exposure pattern to the sub-diffraction limit scale.
[0022] (2) The local photothermal effect effectively suppresses the line expansion and artifact problems caused by the sidelobe energy. Since cross-linking reaction only occurs in areas exceeding the thermal threshold, while areas heated by the sidelobe but not reaching the threshold remain soluble, the clarity of the pattern boundary and the consistency of the line width are ensured, thereby improving the quality of the processed pattern and the stability of the process.
[0023] (3) Since thermal conversion plays a dominant role in the focusing process, the method of this disclosure has lower requirements for the coherence, spectral width, and power stability of the light source. Even with a light source of low coherence, wide spectrum, or low power, a stable super-resolution exposure effect can be obtained. This makes the method of this disclosure applicable to various light source modes such as continuous wave, pulsed laser, or wide field irradiation, significantly broadening its application range.
[0024] (4) The method of this embodiment has great adaptability to the superlens film structure and can adopt metal-dielectric-photoresist-substrate or its multilayer extension design. At the same time, it can be combined with different coupling methods such as gratings, spiral grooves, and periodic arrays, which improves the compatibility of the process. By optimizing the design parameters of the nanodiffraction structure, the excitation efficiency and local field intensity of SPP or related modes can be further improved, thereby enhancing the photothermal synergistic effect.
[0025] (5) Through the photo-thermal synergistic effect, the method of this disclosure achieves higher energy utilization efficiency and reduces the demand for high-power light sources. At the same time, since a lower-cost light source system and a simpler optical configuration can be used, the equipment cost and operating cost of super-resolution lithography are greatly reduced, which is conducive to promoting the industrial application of this technology. Attached Figure Description
[0026] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:
[0027] Figure 1 The schematic diagram illustrates a flow chart of a super-resolution lithography method incorporating localized photothermal effects according to an embodiment of the present disclosure;
[0028] Figure 2 This schematic diagram illustrates the structural process of a super-resolution lithography method incorporating localized photothermal effects according to an embodiment of the present disclosure.
[0029] Figure 3 A schematic diagram of the structure of a five-layer metal-dielectric composite superlens according to an embodiment of the present disclosure is shown.
[0030] Figure 4 This schematically illustrates the relationship between the spiral groove profile and the width as a function of angle in Embodiment 1 of this disclosure;
[0031] Figure 5 This schematically illustrates the light field distribution of a five-layer metal-dielectric composite structure according to an embodiment of the present disclosure in the cross-section of the photoresist layer after irradiation.
[0032] Figure 6 The diagram illustrates the simulation results of optical power distribution and full width at half maximum (FWHM) according to embodiments of the present disclosure.
[0033] Figure 7 This schematically illustrates the temperature distribution of a five-layer metal-dielectric composite structure in the photoresist layer profile after irradiation, according to an embodiment of the present disclosure.
[0034] Figure 8 The illustration schematically shows the temperature distribution of the photoresist center layer and the linewidth exceeding the material conversion threshold of the five-layer metal-dielectric composite structure according to an embodiment of the present disclosure after irradiation. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.
[0036] Figure 1 The illustration shows a schematic flowchart of a super-resolution lithography method incorporating localized photothermal effects according to an embodiment of the present disclosure.
[0037] like Figure 1 As shown, a super-resolution lithography method combining local photothermal effect according to an embodiment of the present disclosure includes steps S1-S6.
[0038] In step S1, a superlens film structure comprising a photoresist layer and at least one metal layer is prepared on a substrate, wherein the photoresist layer comprises a photoresist having thermal crosslinking reaction characteristics.
[0039] In some exemplary embodiments, the superlens film structure includes, but is not limited to, one of the following structures: a metal transmission layer, a photoresist layer, a metal reflection layer and a substrate; a metal transmission layer, a photoresist layer and a substrate; and / or a photoresist layer, a metal reflection layer and a substrate.
[0040] In response to the superlens film structure including a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate, step S110 may specifically include: forming a metal reflection layer on the substrate surface by physical vapor deposition or chemical vapor deposition; spin-coating a photoresist with thermal crosslinking reaction properties onto the metal reflection layer to form a photoresist layer; and forming a metal transmission layer on the photoresist layer by physical vapor deposition or chemical vapor deposition.
[0041] In response to the superlens film structure including a metal transmission layer, a photoresist layer and a substrate, step S110 may specifically include: spin-coating a photoresist with thermal crosslinking reaction properties on the substrate surface to form a photoresist layer; and forming a metal transmission layer on the photoresist layer by means of physical vapor deposition or chemical vapor deposition.
[0042] In response to the superlens film structure including a photoresist layer, a metal reflective layer and a substrate, step S110 may specifically include forming a metal reflective layer on the substrate surface by physical vapor deposition or chemical vapor deposition; and spin-coating a photoresist with thermal crosslinking reaction properties onto the metal reflective layer to form a photoresist layer.
[0043] The metal layer can be a metal reflective layer or a metal transmission layer, preferably a metal material such as Ag, Au, or Al that satisfies the excitation of surface plasmon electromagnetic modes.
[0044] In the embodiments of this disclosure, the photoresist with thermal crosslinking reaction characteristics has a thermal response threshold, a low light absorption coefficient, and a low thermal diffusivity. The photoresist in the photoresist layer has a defined thermal response threshold, which includes either the glass transition temperature or the thermal crosslinking threshold, to ensure stability even after exceeding a critical temperature and to provide strong resistance to development and etching. The photoresist has an extremely low light absorption coefficient within the wavelength range of the illumination source to avoid significant photochemical reactions during exposure, thereby ensuring that thermal effects become the dominant mechanism. Furthermore, to limit its temperature diffusion, the photoresist needs to have a low thermal diffusivity so that locally generated temperature rises can be maintained within the nanoscale without diffusion and loss of spatial resolution. For example, Symcon's S1805 photoresist, mainly composed of phenolic resin, diazonaphthoquinone photosensitizer, and PGMEA solvent, is selected for operation under 532nm laser irradiation. This photoresist has an absorption coefficient of 1.2 × 10⁻⁶ at 532nm. 5 m -1 The thermal diffusivity is approximately 0.2 W / (m·K).
[0045] In step S2, a mask with a nanodiffraction structure is provided, the nanodiffraction structure being configured to cooperate with the superlens film structure to excite surface plasmon electromagnetic modes.
[0046] In embodiments of this disclosure, the mask with a nanodiffraction structure includes a substrate and an absorption layer with a nanodiffraction structure. The absorption layer with a nanodiffraction structure is prepared on the substrate surface by deposition and etching processes. Optionally, before preparing the absorption layer with a nanodiffraction structure on the substrate surface by deposition and etching processes, the geometric parameters of the nanodiffraction structure may be optimized by employing at least one modulation method selected from non-uniform periodic modulation, width modulation, and Gaussian modulation.
[0047] In embodiments of this disclosure, a nanodiffraction structure is used to couple incident light to excite surface plasmons or other surface electromagnetic modes; a photoresist layer is used to form super-resolution patterns through photothermal effects; and a substrate is used to support the structure.
[0048] The embodiments disclosed herein have great adaptability to the superlens film structure and mask. The superlens film structure and mask can be selected as metal-dielectric-photoresist-substrate or its multilayer extension design. At the same time, different coupling methods such as gratings, spiral grooves, and periodic arrays can be combined to improve the excitation and local field intensity of SPP or related modes, thereby enhancing the photo-thermal synergistic effect.
[0049] For example, the combined structure of the superlens film and mask includes one of the following structures: a mask, an air gap layer, a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate stacked sequentially; a mask, a multilayer film structure, an air gap layer, a photoresist layer, and a substrate stacked sequentially; a mask, a multilayer film structure, an air gap layer, a metal transmission layer, a photoresist layer, and a substrate stacked sequentially; a mask, a multilayer film structure, an air gap layer, a photoresist layer, a metal reflection layer, and a substrate stacked sequentially; or a mask, a multilayer film structure, an air gap layer, a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate stacked sequentially. This highly customizable structural design provides great flexibility, allowing optimization according to different resolution targets, light source conditions, and material systems, laying a solid physical foundation for achieving high-performance super-resolution lithography.
[0050] In the embodiments of this disclosure, the nanodiffraction structure includes one of the following: a one-dimensional grating, a two-dimensional grating, a two-dimensional nanoarray, a nanoantenna, a spiral groove, and a radially symmetrical structure. In the design of the nanodiffraction structure, the one-dimensional or two-dimensional grating, due to its periodic arrangement characteristics, can efficiently couple incident light waves and precisely excite electromagnetic modes such as surface plasmon polaritons (SPPs), providing a strongly localized light field for the photolithography process. The two-dimensional nanoarray and nanoantenna, through spatial symmetry, construct a highly uniform and symmetrical local electric field distribution, significantly improving the precision of light field manipulation. The spiral groove structure and the radially symmetrical structure, utilizing their unique geometric topological characteristics, highly concentrate light energy in the central region, forming a high-energy-density focused spot or vortex light field, further enhancing the photolithography resolution. To further optimize performance, techniques such as non-uniform periodic modulation, width gradient design, or Gaussian distribution control can be used to finely adjust the geometric parameters of the nanostructure, thereby improving the uniformity of the light field distribution, enhancing energy coupling efficiency, and ultimately achieving comprehensive optimization of the super-resolution photolithography pattern quality.
[0051] In step S3, the mask is brought close to the substrate, and an illumination source is used to illuminate the mask to excite surface plasmon electromagnetic modes and form a nanoscale localized enhanced light field in the photoresist layer.
[0052] In some exemplary embodiments, step S3 may specifically include: selecting at least one of a continuous wave source or a pulsed source with a wavelength in the deep ultraviolet, ultraviolet, visible, or near-infrared bands as the illumination source; adjusting the polarization state of the illumination source to match the structural properties of the nano-diffraction structure to excite the surface plasmon electromagnetic modes of the nano-diffraction structure; and controlling the power density of the illumination source within 10... 3 The illumination intensity is in the range of W / cm² or higher, and the illumination time is on the order of nanoseconds to milliseconds; wherein, the polarization mode of the illumination source includes at least one of unpolarized, linearly polarized and circularly polarized.
[0053] In the embodiments of this disclosure, the type and polarization direction of the illumination source can be adjusted based on actual needs. By illuminating the nanostructure with light of a specific wavelength, the nanostructure couples with the metal / dielectric interface through its diffraction effect, exciting the localized enhanced light field (SPP). SPP is an electromagnetic wave that propagates along the metal surface, and its field strength decays exponentially in the direction perpendicular to the interface. It can confine the light field energy within a nanoscale space (much smaller than the diffraction limit), forming a "localized enhanced light field."
[0054] For example, a schematic diagram of a nanodiffraction structure with circularly polarized light incident perpendicularly at ultraviolet wavelengths can be found in [reference needed]. Figure 2 (a) In the above, circularly polarized light of ultraviolet wavelength is incident perpendicularly, exciting surface plasmons (SPPs) in the nanofilm layer, generating a strong local electric field focusing within the photoresist layer. See also: Figure 2 (b) in the middle.
[0055] In step S4, the energy of the locally enhanced light field is converted into heat energy through the absorption of light energy by the superlens film structure, resulting in a spatially confined localized temperature rise in the photoresist layer. (See [link to previous section]). Figure 2 (c) in the middle.
[0056] In some exemplary embodiments, step S4 may specifically include: based on the superlens film structure, generating a spatially localized heating source within the photoresist by exciting locally enhanced light power, thereby achieving nanoscale heating control in the photoresist; and based on the low thermal diffusivity of the photoresist, confining the heat energy within the range of the locally enhanced light field to form a temperature rise distribution with a lateral feature size of less than 100 nanometers.
[0057] In the embodiments of this disclosure, the energy of excited SPP and other modes is absorbed by the film structure (especially the metal layer), converting light energy into heat energy through a non-radiative relaxation process. Since the heat energy is generated in the region of strongest local light field, the heat source is naturally confined to the nanoscale, resulting in a "localized temperature rise" in the photoresist that corresponds to the light field distribution but may have a smaller spatial range. By introducing a localized photothermal effect during the excitation process of surface electromagnetic modes such as surface plasmon polaritons (SPP), a synergistic effect of light field focusing or imaging and thermal field modulation is achieved, thereby obtaining an exposure pattern in the photoresist layer that is less than the diffraction limit. The localized photothermal effect creates a spatially confined temperature rise distribution at the focal spot location, equivalent to adding a thermally shrinking window to the optical focusing, which can further compress the focal spot and increase the energy density.
[0058] Therefore, this embodiment not only improves exposure resolution but also enhances the sharpness of pattern boundaries and linewidth consistency. Furthermore, because the portion heated by the side lobes does not exceed the material's threshold, it effectively suppresses line expansion and artifacts caused by side lobe energy. Simultaneously, the scheme of this embodiment reduces dependence on light source conditions. Since thermal conversion plays a dominant role in the focusing process, stable super-resolution exposure effects can be obtained even when using low-coherence, broadband, or low-power light sources. This mechanism is also applicable to various light source modes such as continuous wave, pulsed laser, or wide-field illumination, and can flexibly match different lithography methods, including direct-write, projection, and scanning lithography.
[0059] In step S5, the irradiation parameters of the illumination source are controlled so that the temperature of the photoresist region in the photoresist layer with localized temperature rise exceeds the thermal response threshold and a crosslinking or curing reaction occurs.
[0060] In some exemplary embodiments, step S5 may specifically include: determining the power density and irradiation time of the illumination source based on the thermal response threshold and thermal diffusion characteristics of the photoresist; monitoring the temperature distribution in the photoresist layer in real time to dynamically adjust the power density and irradiation time of the illumination source in real time, controlling the temperature rise amplitude and spatial distribution in the photoresist layer, so that the temperature of the target area exceeds the thermal response threshold and the temperature of the non-target area is lower than the thermal response threshold, wherein the thermal response threshold is the glass transition temperature or thermal crosslinking temperature of the photoresist.
[0061] In the super-resolution lithography method combining local photothermal effect in this embodiment, the real-time temperature distribution of the photoresist layer during the exposure process is monitored and the illumination source parameters are dynamically adjusted according to the monitoring results, which has many significant beneficial effects. On the one hand, it can improve lithography precision and resolution. By accurately controlling the internal temperature changes of the photoresist, the light source parameters can be adjusted accordingly to ensure that the photoresist achieves cross-linking and curing at the optimal temperature distribution, avoiding patterning problems caused by local temperature anomalies and meeting the application requirements of high-precision micro-nano structures. On the other hand, it can enhance process stability and consistency. It can respond promptly to temperature instability or unevenness caused by factors such as light source fluctuations and changes in ambient temperature, automatically correct light source parameters, compensate for the impact of external disturbances, ensure the consistency of lithography processes in different batches and positions, reduce scrap rates, and lower production costs. On the other hand, it can optimize lithography efficiency. It can rationally allocate light source energy according to real-time temperature conditions, increase power or extend exposure time in the heating area but with lower temperature, and reduce power or shorten time in the higher temperature area, avoiding energy waste, shortening exposure time, and improving production efficiency, making it suitable for large-scale industrial production. On the other hand, it can expand the applicability of lithography methods. The real-time monitoring and dynamic adjustment capabilities of this step enable the super-resolution lithography method combined with local photothermal effects to adapt to the needs of various lithography types such as direct-write lithography, interference lithography, or projection lithography, providing flexible and reliable lithography solutions for different fields and application scenarios.
[0062] In step S6, the photoresist layer is developed to remove photoresist areas that have not undergone cross-linking or curing reactions, thereby forming super-resolution nanopatterns.
[0063] The super-resolution lithography method combining local photothermal effects according to embodiments of this disclosure can be used in direct-write lithography, interference lithography, or projection lithography.
[0064] According to the method of this disclosure, when an incident light source irradiates the nanodiffractive structure, the diffracted light couples with the nanofilm superlens structure, exciting surface electromagnetic modes such as surface plasmon polaritons (SPPs), thereby forming a strong localized electromagnetic field at the nanoscale within the film. Unlike traditional photolithography techniques that rely solely on optical diffraction, the method of this disclosure not only utilizes the focusing or imaging characteristics of the light field itself, but also converts light energy into heat energy through the absorption of light energy by the film, thereby inducing a spatially localized temperature rise in the photoresist layer, causing the temperature in specific areas to exceed the thermal threshold temperature of the photoresist. In the subsequent development process, areas where the temperature has not reached the thermal threshold remain soluble, while areas where the local temperature rise exceeds the threshold undergo a physicochemical transformation, forming a cross-linked structure with development resistance, ultimately obtaining super-resolution nanopatterns on the photoresist that exceed the traditional optical diffraction limit.
[0065] Example 1:
[0066] In this embodiment, the nanofilm superlens structure adopts a five-layer metal-dielectric composite superlens structure, see [link to documentation]. Figure 3 ,Depend on Figure 3 The structure of this five-layer metal-dielectric composite superlens consists of, from top to bottom, a top chromium (Cr) film, a first aluminum (Al) layer, a photoresist layer (PR), a second aluminum (Al) layer, and a silicon dioxide substrate (SiO2, thickness ≥200nm). The Cr layer, as a multifunctional top layer, not only acts as a protective film, preventing interference from the external environment to the underlying layers, but also, through its excellent etching characteristics, supports precise subwavelength-scale trench fabrication, laying the foundation for subsequent optical field manipulation. The double-layer Al film design utilizes the surface plasmon resonance effect at the metal-dielectric interface, forming a strong confinement electromagnetic field on the upper and lower surfaces of the photoresist layer through a dual coupling enhancement mechanism, significantly improving the local field strength and providing efficient energy input for photo-thermal conversion. The PR layer, as the photosensitive medium, is the core of the photo-thermal interaction; its thermal response characteristics make it a key carrier for photo-thermal synergy, converting light energy into heat energy to achieve cross-linking and curing of the photoresist. The overall structural design goal is to achieve strong localization and energy concentration of the electromagnetic field within the photoresist layer through interlayer electromagnetic coupling effects.
[0067] Regarding the diffraction structure, two spiral grooves are etched in the top Cr layer. Under circularly polarized light illumination, these grooves efficiently excite surface plasmons and, by introducing angular momentum, achieve phase-matched focusing at the structure's center, resulting in a highly concentrated light field distribution. To further improve focusing symmetry and energy distribution, the groove width is modulated using a Gaussian function that varies with the azimuth angle; see [link to relevant documentation]. Figure 4 The specific function representing the slot width is shown below:
[0068]
[0069] See the diagram illustrating width as a function of angle. Figure 4 ,Depend on Figure 4 It can be seen that the groove width reaches its maximum at the end of the first rotation. Using a Gaussian spiral groove for phase modulation avoids the phase mismatch problem of the uniform groove structure at different azimuth angles, ensuring the uniform distribution of the light field in space.
[0070] Figure 5 This schematically illustrates the light field distribution of a five-layer metal-dielectric composite structure according to an embodiment of the present disclosure in the cross-section of the photoresist layer after irradiation. Figure 6 The diagram illustrates the simulation results of optical power distribution and full width at half maximum (FWHM) according to embodiments of the present disclosure.
[0071] Depend on Figure 5 and Figure 6It can be seen that the Gaussian modulation spiral groove design can significantly improve focusing performance, shrink the full width at half maximum (FWHM) of the focal spot to 43.92nm, improve the uniformity of energy distribution by more than 30%, and make the electric field distribution inside the photoresist more symmetrical. At the same time, the electric field distribution inside the photoresist in the cross section is relatively uniform, and the photolithography produces lines with relatively uniform sidewalls.
[0072] Regarding thermal effect control, this embodiment analyzes the temperature distribution characteristics of the photoresist layer in depth through solid heat transfer simulation under transient illumination conditions.
[0073] Figure 7 This schematically illustrates the temperature distribution of a five-layer metal-dielectric composite structure in the photoresist layer profile after irradiation, according to an embodiment of the present disclosure. Figure 8 The illustration schematically shows the temperature distribution of the photoresist center layer and the simulation results of linewidth exceeding the material threshold of a five-layer metal-dielectric composite structure according to an embodiment of the present disclosure after irradiation.
[0074] Depend on Figure 7 and Figure 8 It is known that by placing the optimized structure under transient illumination conditions, the incident light power acts on the photoresist layer through a solid heat transfer module, yielding its transient temperature distribution. Using a 15W laser for ultrafast irradiation, simulation results show that the localized heating region is highly concentrated, with the width of the region above the photoresist glass transition temperature (156℃) being only about 21.46nm, nearly doubling the spatial resolution compared to traditional methods. This breakthrough achieves a high-contrast light intensity distribution in the photoresist layer by employing a Gaussian-distributed excitation structure and a co-designed film layer, significantly improving the precision of photoresist thermal crosslinking and making it possible to realize sub-10nm scale photolithographic patterns.
[0075] In summary, this embodiment achieves synergistic optimization of the light and thermal fields through the innovative combination of a five-layer metal-dielectric composite superlens structure and a Gaussian-modulated spiral groove. It exhibits significant advantages in terms of lithography resolution, pattern quality, and process stability, laying a solid foundation for the industrial application of super-resolution lithography technology.
[0076] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of this disclosure. It should be understood that the above are only specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.
Claims
1. A super-resolution lithography method incorporating localized photothermal effects, characterized in that, include: A superlens film structure comprising a photoresist layer and at least one metal layer is fabricated on a substrate, wherein the photoresist layer comprises a photoresist having thermal crosslinking reaction characteristics; A mask with a nanodiffraction structure is provided, the nanodiffraction structure being configured to cooperate with the superlens film structure to excite surface plasmon electromagnetic modes; The mask is brought close to the substrate, and an illumination source is used to illuminate the mask to excite the surface plasmon electromagnetic mode and form a nanoscale localized enhanced light field in the photoresist layer. By absorbing light energy through the superlens film structure, the energy of the locally enhanced light field is converted into heat energy, resulting in a spatially confined local temperature rise in the photoresist layer. The irradiation parameters of the illumination source are controlled so that the temperature of the photoresist region in the photoresist layer with localized temperature rise exceeds the thermal response threshold and a crosslinking or curing reaction occurs. The photoresist layer is developed to remove areas of photoresist that have not undergone cross-linking or curing reactions, thereby forming super-resolution nanopatterns.
2. The method according to claim 1, characterized in that, The photoresist with thermal crosslinking reaction properties has a thermal response threshold, a low light absorption coefficient, and a low thermal diffusivity. The light absorption coefficient of the photoresist with thermal crosslinking reaction properties is less than 1.2 × 10⁻⁶ in the illumination source wavelength range. 5 m -1 The thermal diffusivity is less than 0.2 W / (m·K).
3. The method according to any one of claims 1, characterized in that, The superlens film structure includes, but is not limited to, one of the following structures: Metal transmission layer, photoresist layer, metal reflective layer, and substrate; Metal transmission layer, photoresist layer and substrate; Photoresist layer, metal reflective layer and substrate.
4. The method according to claim 3, characterized in that, The method for fabricating a superlens film structure comprising a photoresist layer and at least one metal layer on a substrate includes: In response to the superlens film structure comprising a metal transmission layer, a photoresist layer, a metal reflection layer, and a substrate, the method includes: A metallic reflective layer is formed on the substrate surface using physical vapor deposition or chemical vapor deposition methods; The photoresist with thermal crosslinking reaction properties is spin-coated onto the metal reflective layer to form a photoresist layer; A metal transmission layer is formed on the photoresist layer by means of physical vapor deposition or chemical vapor deposition. or In response to the superlens film structure comprising a metal transmission layer, a photoresist layer, and a substrate, the method includes: The photoresist with thermal crosslinking reaction properties is spin-coated onto the substrate surface to form a photoresist layer; A metal transmission layer is formed on the photoresist layer by means of physical vapor deposition or chemical vapor deposition. or In response to the superlens film structure comprising a photoresist layer, a metal reflective layer, and a substrate, the method includes: A metallic reflective layer is formed on the substrate surface using physical vapor deposition or chemical vapor deposition methods; The photoresist with thermal crosslinking reaction properties is spin-coated onto the metal reflective layer to form a photoresist layer.
5. The method according to claim 1, characterized in that, The mask with a nanodiffraction structure includes a substrate and an absorption layer with a nanodiffraction structure. The absorption layer with a nanodiffraction structure is prepared on the surface of the substrate by deposition and etching processes.
6. The method according to claim 5, characterized in that, Prior to the preparation of the absorption layer with the nanodiffraction structure on the substrate surface by deposition and etching processes, the following steps are also included: The geometric parameters of the nanodiffraction structure are optimized by employing at least one of the following modulation methods: non-uniform periodic modulation, width modulation, and Gaussian modulation.
7. The method according to any one of claims 1 to 6, characterized in that, The nanodiffraction structure includes one of the following: a one-dimensional grating, a two-dimensional grating, a two-dimensional nanoarray, a nanoantenna, a spiral groove, and a radially symmetrical structure.
8. The method according to any one of claims 1 to 6, characterized in that, The step of illuminating the mask with an illumination source includes: Choose at least one of the following as the illumination source: a continuous wave light source or a pulsed light source with a wavelength in the deep ultraviolet band, ultraviolet band, visible band or near-infrared band. The polarization state of the illumination source is adjusted to match the symmetry of the nano-diffraction structure in order to excite the surface plasmon electromagnetic mode of the nano-diffraction structure. Control the power density of the lighting source at 10 3 The illumination time of the light source is in the range of W / cm² or higher, and the illumination time is in the order of nanoseconds to milliseconds. The polarization mode of the illumination source includes at least one of non-polarized, linearly polarized, and circularly polarized.
9. The method according to any one of claims 1 to 6, characterized in that, The process of converting the energy of the locally enhanced light field into heat energy through the absorption of light energy by the superlens film structure includes: Based on the superlens film structure, a spatially localized heating source is generated in the photoresist by exciting locally enhanced optical power, thereby achieving nanoscale heating control in the photoresist. Based on the low thermal diffusivity of the photoresist, the thermal energy is confined within the range of the localized enhanced light field, forming a temperature rise distribution with a lateral feature size of less than 100 nanometers.
10. The method according to any one of claims 1 to 6, characterized in that, The control of the illumination parameters of the lighting source, causing the temperature of the photoresist region in the photoresist layer to exceed the thermal response threshold and undergo a crosslinking or curing reaction, includes: Based on the thermal response threshold and thermal diffusion characteristics of the photoresist, the power density and irradiation time of the illumination source are determined; The temperature distribution within the photoresist layer is monitored in real time to dynamically adjust the power density and irradiation time of the illumination source, thereby controlling the temperature rise and spatial distribution within the photoresist layer. This ensures that the temperature in the target area exceeds the thermal response threshold while the temperature in the non-target area remains below the thermal response threshold. The thermal response threshold is the glass transition temperature or thermal crosslinking temperature of the photoresist.
11. An application of the super-resolution lithography method combining localized photothermal effects as described in any one of claims 1-10, characterized in that, The super-resolution lithography method combining local photothermal effects is used in direct-write lithography, interference lithography, or projection lithography.