Deep ultraviolet grid polarizer and method of making the same

Abstract

The present application relates to a kind of deep ultraviolet grating polarizers and preparation method thereof, belong to polarizer technical field, including from bottom to top sequentially connected substrate, first dielectric layer, second dielectric layer and interval setting line grid on the upper surface of second dielectric layer, the upper surface of second dielectric layer between adjacent line grid is provided with metal layer, line grid includes from bottom to top sequentially connected first dielectric layer, second dielectric layer and metal layer;The present application is by adding high low refractive index alternately between substrate and metal line grid first, second dielectric layer, and metal layer is set on the upper surface of second dielectric layer in line grid gap, constructs the medium-metal composite structure with resonance coupling effect.The design effectively controls the equivalent optical admittance of deep ultraviolet band, significantly enhances the transmittance of TE polarized light, while maintaining the efficient inhibition to TM polarization, so as to improve the polarization efficiency while reducing metal absorption loss.As a whole, the polarizer has the advantages of high transmittance, high extinction ratio and the like.

Description

Technical Field

[0001] This invention belongs to the field of polarizer technology, and specifically relates to a deep ultraviolet grating polarizer and its preparation method. Background Technology

[0002] As the feature size of large-scale integrated circuits continues to evolve towards smaller nodes, immersion ArF lithography systems, with their combination of 193nm deep ultraviolet light sources and high numerical aperture technology, have established a core position in the field of advanced chip manufacturing. In this type of lithography system, the polarization state of the illumination beam plays a decisive role in imaging contrast, depth of focus, and resolution. When the numerical aperture of the projection lens exceeds 0.95, unpolarized illumination alone is no longer sufficient to meet the imaging quality requirements; polarized illumination technology must be introduced to control the polarization state of the illumination light to achieve the desired lithographic resolution.

[0003] Achieving effective manipulation of polarization states in the deep ultraviolet band has long faced dual constraints in terms of materials and structure. Traditional polarization beam-splitters are no longer usable at 193 nm. Against this backdrop, subwavelength wire grating polarization structures have come into the researchers' view. For a one-dimensional metal wire grating, when the grating period is much smaller than the operating wavelength, the component of the incident light with the electric field direction parallel to the metal line (TE polarization) is strongly reflected due to the induced surface current, while the component with the electric field direction perpendicular to the grating (TM polarization) is approximately transmitted, thus achieving the separation of the two orthogonal polarization states. However, when using wavelengths extended to the 193 nm deep ultraviolet band, the period of the metal wire grating polarization device needs to be less than 50 nm to achieve good polarization performance, which poses a significant challenge to current micro-nano fabrication processes.

[0004] The issue of material selection is equally complex. Aluminum wire gratings, which dominate the visible and near-infrared fields, exhibit significantly altered optical properties as the wavelength extends into the ultraviolet region, failing to maintain their extinction ratio at 193 nm. Tungsten wire gratings showed relatively better optical behavior in this band, but a trade-off between transmittance and extinction ratio still exists. Literature analysis indicates that the upper limit of the extinction ratio of metal wire gratings in the deep ultraviolet band is inherently constrained by the ratio of the real to imaginary parts of the material's complex permittivity; simply optimizing the geometric parameters of the metal wire grating cannot overcome the boundaries set by the intrinsic properties of the material.

[0005] To achieve polarization performance comparable to that of visible and near-infrared bands in deep ultraviolet grating polarization devices, it is necessary to design polarization devices with more complex wire grating structures. This invention provides a deep ultraviolet grating polarizer and its fabrication method. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a deep ultraviolet grating polarizer and its fabrication method, thereby improving the TE polarization transmittance and extinction ratio of the deep ultraviolet grating polarizer.

[0007] To achieve the above objectives, the present invention provides the following solution: A deep ultraviolet grating polarizer includes a substrate, a first dielectric layer, a second dielectric layer, and a wire grid disposed on the upper surface of the second dielectric layer from bottom to top. A metal layer is disposed on the upper surface of the second dielectric layer between adjacent wire grids. The wire grid includes the first dielectric layer, the second dielectric layer, and the metal layer disposed from bottom to top.

[0008] Preferably, the top surface of the metal layer located between adjacent wire grids is within the height range of the second dielectric layer of the wire grid, and the two sides of the metal layer located between adjacent wire grids are in contact with the outer wall of the wire grid.

[0009] Preferably, the substrate is fused silica.

[0010] Preferably, the thickness of the fused silica is greater than 0.5 mm.

[0011] Preferably, the first dielectric layer is made of magnesium fluoride, the second dielectric layer is made of silicon dioxide, and the metal layer is made of aluminum.

[0012] Preferably, the thickness of the first dielectric layer and the second dielectric layer located below the wire gate is 20 nm to 200 nm, the thickness of the first dielectric layer and the second dielectric layer located within the wire gate is 15 nm to 150 nm, and the thickness of the metal layer located within the wire gate is 20 nm to 180 nm.

[0013] Preferably, the widths of the first dielectric layer, the second dielectric layer, and the metal layer located within the wire grid are the same, ranging from 40 mm to 100 mm.

[0014] Preferably, the period is twice the width of the wire grid.

[0015] A method for fabricating a deep ultraviolet grating polarizer includes the following steps: The first dielectric layer, the second dielectric layer, the first dielectric layer, and the second dielectric layer are sequentially deposited on the substrate; Photoresist is spin-coated onto the upper surface of the topmost second dielectric layer to form a photoresist layer; Photolithography is performed on the photoresist layer, followed by development and etching to form a wire grid structure; Remove the remaining photoresist and deposit the metal layer on the surface of the second dielectric layer of the grid; A deep ultraviolet grating polarizer was obtained.

[0016] Preferably, the coating method is vacuum evaporation, magnetron sputtering, ion plating, chemical vapor deposition, or atomic layer deposition.

[0017] The present invention achieves the following technical effects compared to the prior art: This invention constructs a dielectric-metal composite structure with resonant coupling effect by adding alternating high and low refractive index first and second dielectric layers between the substrate and the metal grid, and placing a metal layer on the upper surface of the second dielectric layer in the grid gap. This design effectively modulates the equivalent optical admittance in the deep ultraviolet band, significantly enhances the transmittance of TE polarized light, and maintains efficient suppression of TM polarization, thereby improving polarization efficiency while reducing metal absorption loss. Overall, this polarizer combines advantages such as high transmittance, high extinction ratio, strong deep ultraviolet applicability, and good process compatibility, making it suitable for cutting-edge applications such as advanced photolithography, deep ultraviolet spectroscopy analysis, and high-density optical storage. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a cross-sectional view of the present invention; Figure 2 The simulation results of the transmittance and extinction ratio of TE polarized light and TM polarized light in the 150-300nm deep ultraviolet band are presented in this invention. Figure 3 The simulation results are for the three periodic structures under TE polarization and TM polarization conditions of this invention. Figure 4 The preparation process of this invention is as follows; The components are: 1. substrate; 2. first dielectric layer; 3. metal layer; 4. second dielectric layer; and 5. photoresist layer. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a deep ultraviolet grating polarizer and its preparation method, which aims to improve the TE polarization transmittance and extinction ratio of the deep ultraviolet grating polarizer.

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] refer to Figure 1 A deep ultraviolet grating polarizer includes a substrate 1, a first dielectric layer 2, a second dielectric layer 4, and wire grids arranged at intervals on the upper surface of the second dielectric layer 4, connected sequentially from bottom to top. A metal layer 3 is disposed on the upper surface of the second dielectric layer 4 between adjacent wire grids. The wire grids include the first dielectric layer 2, the second dielectric layer 4, and the metal layer 3 connected sequentially from bottom to top. Specifically, the substrate 1 is made of a material with high transmittance in the deep ultraviolet band, and the upper and lower surfaces of the substrate 1 are polished, with a surface roughness of less than 1. nm, to reduce scattering loss; the first dielectric layer 2 is disposed on the substrate 1, using a low refractive index dielectric material, to provide a refractive index buffer transition and reduce Fresnel reflection between the substrate 1 and the upper layer; the second dielectric layer 4 is disposed on the first dielectric layer 2, using a high refractive index dielectric material, the first dielectric layer 2 and the second dielectric layer 4 constitute an antireflection film stack with alternating high and low refractive indices, together forming an optical resonant cavity or guided mode resonant coupling structure; the wire grid is spaced on the upper surface of the second dielectric layer 4, and the structure consists of a three-layer stacked structure composed of the first dielectric layer 2, the second dielectric layer 4 and the metal layer 3 from bottom to top, that is, the wire grid itself reuses the material of the lower layer film; the metal layer 3 is also disposed on the upper surface of the second dielectric layer 4 between adjacent wire grids (i.e., the bottom of the trench) and on the top of the wire grid as a cover layer; the present invention constructs a dielectric-metal composite structure with resonant coupling effect by adding a first and second dielectric layer 4 with alternating high and low refractive indices between the substrate 1 and the metal wire grid, and disposing a metal layer 3 on the upper surface of the second dielectric layer 4 in the wire grid gap. This design effectively modulates the equivalent optical admittance in the deep ultraviolet band, significantly enhancing the transmittance of TE-polarized light while maintaining efficient suppression of TM polarization. This results in improved polarization efficiency while reducing metal absorption losses. Overall, this polarizer combines advantages such as high transmittance, high extinction ratio, strong deep ultraviolet applicability, and good process compatibility, making it suitable for cutting-edge applications in advanced lithography, deep ultraviolet spectroscopy, and high-density optical storage.

[0024] refer to Figure 1The top surface of the metal layer 3 located between adjacent grids is situated within the height range of the second dielectric layer 4 of the grids, and both sides of the metal layer 3 between adjacent grids are in contact with the outer wall of the grids. Specifically, by precisely limiting the height of the top surface of the metal layer 3 at the bottom of the adjacent grid trench within the height range of the second dielectric layer 4 (high refractive index layer) of the grids, and ensuring seamless contact between the two sides of the metal layer 3 and the dielectric sidewall of the grids, a "dielectric height-matched" metal absorption trench is constructed. This structure places the metal layer 3 at a specific spatial position in the dielectric film stack where the TE polarization field strength is weak and the TM polarization field strength is strong, enabling the metal layer 3 to exhibit strong selective absorption and reflection suppression of TM polarization. Simultaneously, since the metal layer 3 does not extend to the top metal layer 3 of the grids and does not obstruct the main transmission channel of TE polarization, the TE polarization transmittance is almost unaffected, thus achieving simultaneous optimization of high extinction ratio and high TE transmittance in the deep ultraviolet band. Furthermore, this height limitation avoids potential interference of the metal layer 3 to the first dielectric layer 2 and the substrate 1, simplifying the fabrication process and improving structural tolerance.

[0025] Furthermore, substrate 1 is fused silica; the core purpose is to utilize its high transmittance, low absorption loss, and zero birefringence in the deep ultraviolet band to provide an "optically transparent" structural basis for the efficient transmission of TE polarized light. Simultaneously, its low coefficient of thermal expansion, high thermal conductivity, and excellent resistance to deep ultraviolet radiation ensure the dimensional stability and thermal reliability of the wire grating subwavelength structure during fabrication and use. In addition, the chemical inertness, high surface flatness, and good thermal matching with the dielectric film of fused silica ensure the feasibility of device fabrication and long-term environmental tolerance. In summary, fused silica substrate 1 achieves the best balance between optical performance, thermomechanical stability, process compatibility, and economy, making it an ideal substrate choice for realizing high-performance, long-life, and low-cost deep ultraviolet grating polarizers.

[0026] Furthermore, the thickness of the fused silica is greater than 0.5 mm; this ensures that the device has sufficient mechanical strength and structural rigidity during fabrication and use, preventing bending or cracking due to excessively thin substrate 1 under thin film stress, thermal stress, and external forces, thereby guaranteeing the morphological accuracy and optical performance stability of the wire grid subwavelength structure. At the same time, sufficient thickness also provides good heat capacity and heat dissipation path, which helps to absorb and dissipate the heat generated by deep ultraviolet irradiation, reducing the risk of temperature rise and thermal drift in the wire grid region. In addition, this thickness facilitates subsequent cutting, clamping, and packaging operations, taking into account both process feasibility and device reliability, and improving the engineering practicality and service life of the device in the most direct and effective way without significantly increasing optical absorption loss.

[0027] Furthermore, the first dielectric layer 2 is made of magnesium fluoride, the second dielectric layer 4 is made of silicon dioxide, and the metal layer 3 is made of aluminum. In the deep ultraviolet grating polarizer, magnesium fluoride (MgF2) is selected as the first dielectric layer 2, silicon dioxide (SiO2) as the second dielectric layer 4, and aluminum (Al) as the metal layer 3. The core purpose is to construct an optimal material combination that combines high transmission enhancement and high polarization selectivity in the deep ultraviolet band. Magnesium fluoride, as a low refractive index material, has a refractive index close to that of the fused silica substrate 1, which can form a smooth optical transition and reduce interface reflection. Silicon dioxide, as a high refractive index material, forms an antireflection film stack with magnesium fluoride alternating between high and low refractive indices. Both have extremely low absorption coefficients and excellent radiation resistance stability in the deep ultraviolet band, which can effectively control the transmission phase of TE polarized light and enhance its transmittance. Aluminum, as the metal layer 3, has relatively high reflectivity and acceptable absorption loss in the deep ultraviolet band. Moreover, it has mature technology, good adhesion, and can provide sufficient conductivity and plasma response to efficiently suppress the transmission of TM polarized light. The three elements work synergistically to enhance the light transmission of TE polarization through the dielectric film stack, while ensuring the effective suppression of TM polarization by the metal wire grid. At the same time, the selected materials all have good deep ultraviolet stability, film adhesion, and process compatibility, thus achieving the best balance between optical performance, environmental reliability, and manufacturing maturity.

[0028] Furthermore, the thickness of the first dielectric layer 2 and the second dielectric layer 4 located below the wire grid is 20 nm to 200 nm, the thickness of the first dielectric layer 2 and the second dielectric layer 4 located inside the wire grid is 15 nm to 150 nm, and the thickness of the metal layer 3 located inside the wire grid is 20 nm to 180 nm. Specifically, the thickness of the dielectric layer (continuous film stack) below the wire grid is 20~200 nm, covering 1 / 10 to 2 / 3 of the deep ultraviolet working wavelength (200~300 nm), which is sufficient to form an effective anti-reflection resonant cavity, enabling TE polarized light to obtain phase compensation and field strength enhancement before passing through the metal wire grid, while avoiding increased absorption or stress accumulation caused by excessive film thickness; the thickness of the dielectric layer inside the wire grid is reduced to 15~150 nm. The thickness of the dielectric layer on the sidewall of the grid is slightly smaller than the continuous film layer below due to the etching process. This range ensures that the "dielectric core" of the grid provides refractive index guidance without making the overall height of the grid too large, resulting in an excessive aspect ratio and structural collapse. The thickness of the metal layer 3 inside the grid is 20~180 nm, which takes into account both the skin depth (about 10~20 nm) in the deep ultraviolet band and the effective suppression of TM polarization. Too thin (<20 nm) will lead to insufficient TM polarization reflection and a decrease in extinction ratio, while too thick (>180 nm) will increase the absorption loss of TE polarization and the difficulty of fabrication and etching.

[0029] The three thickness ranges work synergistically to ensure precise matching of the antireflection phase of the dielectric film stack and the polarization selection of metal layer 3 at the same wavelength. Simultaneously, they control the total height of the wire grating within a reasonable range (approximately 50–480 nm), maintaining its aspect ratio (height / width) within a fabricable process window and avoiding the risk of collapse during development, drying, or cleaning of high aspect ratio structures. In summary, this thickness constraint represents the optimal trade-off between optical performance (high transmittance, high extinction ratio), structural reliability (collapse resistance, stress resistance), and process yield, providing a crucial dimensional design boundary for the stable mass production and practical application of deep ultraviolet grating polarizers.

[0030] Furthermore, the first dielectric layer 2, the second dielectric layer 4, and the metal layer 3 located within the grid have the same width, ranging from 40 mm to 100 mm; the purpose is to construct a geometrically symmetrical, vertically aligned "columnar" composite grid structure. The equal width of the three layers ensures a uniform refractive index distribution along the height direction of the grid, avoiding TE polarization scattering loss and TM / TE mode coupling caused by abrupt width changes or lateral misalignment, thus achieving a high extinction ratio while maintaining high transmittance. Simultaneously, the vertically steep, equal-width sidewalls eliminate overhang or "mushroom head" structural defects, significantly improving the grid's resistance to collapse during fabrication and subsequent use. Moreover, this width range is highly compatible with the resolution and tolerance of current deep ultraviolet lithography and etching processes, simplifying the fabrication process and improving yield.

[0031] Furthermore, the period is twice the width of the grid; through the precise design of the "ridge-slit" geometric symmetry, an optimal trade-off is achieved between optical performance and process feasibility. From an optical perspective, this ratio allows TE-polarized light to form a stable standing wave enhancement resonance in the slit to achieve high transmittance, while maximizing the metallic cutoff effect of TM-polarized light to achieve a high extinction ratio, achieving the best balance between extinction ratio and transmittance. Moreover, the symmetrical structure eliminates even-order diffraction and reduces angular sensitivity. From a process perspective, the 1:1 mask duty cycle and equal-width trench design are most conducive to high-resolution lithography and anisotropic etching, effectively avoiding process defects such as proximity effect, etching hysteresis, and sidewall tilt, and improving the consistency and yield of the fabrication.

[0032] refer to Figure 4 The method for fabricating the deep ultraviolet grating polarizer of the present invention is as follows: A first dielectric layer 2, a second dielectric layer 4, a first dielectric layer 2, and a second dielectric layer 4 are sequentially deposited on a substrate 1; Photoresist is spin-coated onto the upper surface of the topmost second dielectric layer 4 to form a photoresist layer 5; Photolithography is performed on the photoresist layer 5, followed by development and etching to form a grid structure; Remove the remaining photoresist and deposit a metal layer 3 on the surface of the second dielectric layer 4 of the inline gate; A deep ultraviolet grating polarizer was obtained.

[0033] Furthermore, the coating methods include vacuum evaporation, magnetron sputtering, ion plating, chemical vapor deposition, or atomic layer deposition.

[0034] refer to Figure 2 Simulation results of the transmittance and extinction ratio of TE-polarized and TM-polarized light from a deep ultraviolet (DEUV) grating polarizer in the 150-300 nm DEUV band are presented. These results were obtained using the finite-difference time-domain (FDTD) simulation software LumericalFDTD. The refractive index of metal layer 3 in the simulation was obtained from the built-in LumericalFDTD software, while the refractive indices of other dielectric materials and substrate 1 were obtained from the refractiveindex.info website. The structural parameters of the DEUV grating polarizer were optimized using a particle swarm optimization algorithm. The resulting structural parameters are: height h1 30-50 nm, height h2 40-80 nm, height h3 30-80 nm, height h4 40-90 nm, height h5 70-100 nm, width W 60-95 nm, and the period P of the DEUV grating polarizer is twice W. Figure 2 The simulation results show that at a wavelength of 193 nm, the TE transmittance of the deep ultraviolet grating polarizer is 72%, and the extinction ratio is 43.63 dB. These simulation results demonstrate that the optimized deep ultraviolet grating polarizer in this invention can effectively control the polarization of the 193 nm deep ultraviolet light source in an immersion ArF lithography system.

[0035] Figure 3 Simulation results for three periodic structures under TE and TM polarization conditions are presented. The 0nm position in the x-direction of the figure corresponds to the center of the second dielectric layer 4 and the first dielectric layer 2 within the wire grating. In the electromagnetic field distribution diagram for TE polarized light, the electric field energy is mainly concentrated in the air cavity between the wire gratings. It then propagates along the interface between the metal and dielectric materials and is introduced into the second dielectric layer 4 and the first dielectric layer 2 within the wire grating, forming a standing wave that propagates into the substrate 1. Therefore, TE polarized light is transmitted. For TM polarized light, the electric field energy is mainly concentrated on the edges and surface of the Al metal. This is a surface plasmon resonance mode that only propagates on the Al metal surface and does not transmit the TM polarized light into the dielectric material. Therefore, TM polarized light is only reflected.

[0036] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0037] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A deep ultraviolet grating polarizer, characterized in that, It includes a substrate, a first dielectric layer, a second dielectric layer, and wire grids arranged at intervals on the upper surface of the second dielectric layer, which are connected sequentially from bottom to top. A metal layer is disposed on the upper surface of the second dielectric layer between adjacent wire grids. The wire grids include the first dielectric layer, the second dielectric layer, and the metal layer connected sequentially from bottom to top.

2. The deep ultraviolet grating polarizer according to claim 1, characterized in that, The top surface of the metal layer located between adjacent wire grids is within the height range of the second dielectric layer of the wire grids, and the two sides of the metal layer located between adjacent wire grids are in contact with the outer wall of the wire grids.

3. The deep ultraviolet grating polarizer according to claim 1, characterized in that, The substrate is fused silica.

4. The deep ultraviolet grating polarizer according to claim 3, characterized in that, The thickness of the fused silica is greater than 0.5 mm.

5. The deep ultraviolet grating polarizer according to claim 1, characterized in that, The first dielectric layer is made of magnesium fluoride, the second dielectric layer is made of silicon dioxide, and the metal layer is made of aluminum.

6. The deep ultraviolet grating polarizer according to claim 1, characterized in that, The thickness of the first dielectric layer and the second dielectric layer located below the wire gate is 20 nm to 200 nm, the thickness of the first dielectric layer and the second dielectric layer located within the wire gate is 15 nm to 150 nm, and the thickness of the metal layer located within the wire gate is 20 nm to 180 nm.

7. The deep ultraviolet grating polarizer according to claim 1, characterized in that, The first dielectric layer, the second dielectric layer, and the metal layer located within the wire grid have the same width, ranging from 40 mm to 100 mm.

8. The deep ultraviolet grating polarizer according to claim 7, characterized in that, The period is twice the width of the wire grid.

9. A method for fabricating a deep ultraviolet grating polarizer, characterized in that, The application of the deep ultraviolet grating polarizer according to any one of claims 1 to 8 includes the following steps: The first dielectric layer, the second dielectric layer, the first dielectric layer, and the second dielectric layer are sequentially deposited on the substrate; Photoresist is spin-coated onto the upper surface of the topmost second dielectric layer to form a photoresist layer; Photolithography is performed on the photoresist layer, followed by development and etching to form a wire grid structure; Remove the remaining photoresist and deposit the metal layer on the surface of the second dielectric layer of the grid; A deep ultraviolet grating polarizer was obtained.

10. The method for fabricating a deep ultraviolet grating polarizer according to claim 9, characterized in that, The coating methods include vacuum evaporation, magnetron sputtering, ion plating, chemical vapor deposition, or atomic layer deposition.

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