Off-axis illumination photoetching mask, preparation method thereof and photoetching system

Abstract

The invention provides an off-axis illumination photoetching mask, a preparation method thereof and a photoetching system, which can be applied to the technical field of micro-nano machining and advanced photoetching, and the photoetching mask comprises a mask substrate comprising a first surface and a second surface which are oppositely arranged; the photoetching mask pattern structure is located on the second surface of the mask substrate; the light incident part is located on the first surface of the mask substrate, and the light incident part comprises a plurality of light incident units which are periodically arranged; wherein the light incident unit is provided with a V-shaped structure in the direction perpendicular to the first surface, the V-shaped structure gradually shrinks inwards from the first surface to the second surface, and each V-shaped structure comprises two slope surfaces which are connected with each other; the light incident part further comprises a band-pass filtering film which at least covers the two slope faces of the V-shaped structure.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of micro-nano processing and advanced lithography, and particularly relates to an off-axis illumination lithography mask, a preparation method thereof and a lithography system. BACKGROUND

[0002] In the field of semiconductor manufacturing and micro-nano processing, lithography technology is the core process of pattern transfer, and its resolution and imaging quality directly determine the feature size and integration of the device. High numerical aperture (High-NA) illumination is one of the key means to improve the resolution and imaging contrast of lithography. At present, the main technical paths to realize high numerical aperture illumination include oblique incidence illumination, prism coupling reflection illumination, and diffraction illumination based on grating structure, etc.

[0003] Oblique incidence and prism reflection methods are widely used due to their relatively simple structure and low cost, and can achieve high numerical aperture illumination close to the refractive index of prism materials. However, such methods have high requirements for the transmittance of optical elements in the optical path. In the deep ultraviolet band, high refractive index materials often have strong light absorption effect, for example, the absorption coefficient of titanium dioxide and diamond-like film materials is high in the ultraviolet band, which leads to a decrease in overall light energy utilization and limits their application in high-efficiency exposure processes.

[0004] On the other hand, the illumination scheme based on grating or periodic lattice structure can excite larger wave vector components through diffraction effect, thereby realizing high numerical aperture illumination. However, such methods face a significant problem in practical application: the light intensity of 0-order diffraction light is usually significantly higher than that of ±1-order diffraction light, causing a decrease in imaging contrast. How to obtain effective high-order diffraction light while suppressing or eliminating the interference of 0-order light has become a difficult problem to be solved in this technical route.

[0005] In summary, the existing high numerical aperture illumination schemes have different degrees of limitations in material transmittance, energy utilization efficiency and imaging contrast, etc. Therefore, it is urgent to develop a new type of high numerical aperture illumination lithography mask structure and its preparation method. SUMMARY

[0006] (I) Technical problems to be solved

[0007] To solve at least one of the above technical problems in the prior art, embodiments of the present disclosure provide an off-axis illumination photomask, a preparation method thereof, and a photolithography system. By constructing light entry units on the first surface of the mask substrate and covering a band-pass filter film, the vertical incident light is efficiently converted into high numerical aperture off-axis illumination. The geometric optical effect of the V-shaped structure and the angle selection characteristic of the band-pass filter film are synergistically used to flexibly control the dipole, quadrupole, and annular illumination. Not only is the imaging contrast improved by 40-60% and the numerical aperture increased to 0.8-1.5, but also the optical system is greatly simplified and the manufacturing cost is reduced through the integrated structure, while the energy utilization rate is increased by about 30%. The scheme is compatible with the standard semiconductor process, supports multi-band light sources and various working environments, effectively solves the technical bottlenecks of complex structure, high cost, and low efficiency of traditional high numerical aperture illumination systems, and provides a breakthrough technical path for advanced photolithography process.

[0008] (II) TECHNICAL SCHEME

[0009] To solve the above technical problems, embodiments of the present disclosure provide an off-axis illumination photomask, a preparation method thereof, and a photolithography system.

[0010] According to a first aspect of the present disclosure, an off-axis illumination photomask is provided, comprising: a mask substrate comprising a first surface and a second surface arranged oppositely; a photomask pattern structure located on the second surface of the mask substrate; a light entry part located on the first surface of the mask substrate, the light entry part comprising a plurality of periodically arranged light entry units; wherein the light entry unit comprises a recess structure, the recess structure has a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure gradually shrinks in a direction from the first surface to the second surface, each V-shaped structure comprises two interconnected slope surfaces; the light entry part further comprises a band-pass filter film, the band-pass filter film covers at least the two slope surfaces of the V-shaped structure.

[0011] In some exemplary embodiments, the recess structure comprises a lateral triangular prism structure, an inverted quadrangular pyramid structure, or an inverted conical structure.

[0012] In some exemplary embodiments, when the recess structure is a lateral triangular prism structure and arranged in a one-dimensional grating, the light entry part can form dipole illumination; when the recess structure is an inverted quadrangular pyramid structure and arranged in a two-dimensional array, the light entry part can form quadrupole illumination; when the recess structure is an inverted conical structure and arranged in a two-dimensional array, the light entry part can form annular illumination.

[0013] In some exemplary embodiments, the band-pass filter film is a Fabry-Perot type interference filter multilayer structure; the band-pass filter film is configured to have high reflectivity for illumination light vertically incident to the surface of the band-pass filter film, and high transmittance for illumination light incident at a specific oblique angle after reflection.

[0014] In some exemplary embodiments, the Fabry-Perot type interference filter multilayer structure is an all-dielectric type, which is formed by alternating stacking of high refractive index dielectric layers and low refractive index dielectric layers to form a distributed Bragg reflector, and a dielectric resonant cavity layer is disposed therein.

[0015] In some exemplary embodiments, the Fabry-Perot type interference filter multilayer structure is a metal-dielectric hybrid type, including two reflective layers made of metal material and a dielectric resonant cavity layer sandwiched between the two reflective layers.

[0016] In some exemplary embodiments, the angle between the normal of the ramp surface of the V-shaped structure and the direction of the illumination light incident perpendicular to the first surface of the mask substrate is 45° to 75°.

[0017] In some exemplary embodiments, the total number of layers in the bandpass filter film is 2 to 100; the thickness of a single layer in the bandpass filter film is 5 nm to 300 nm; and the total thickness of the bandpass filter film is 30 nm to 3000 nm.

[0018] According to a second aspect of this disclosure, a method for fabricating the aforementioned off-axis illumination photolithography mask is provided, comprising: step S1, forming a photolithography mask pattern structure with a preset pattern on a second surface of a mask substrate; step S2, forming a light-incident portion comprising a plurality of periodically arranged light-incident units on a first surface of the mask substrate, including a recessed structure, the recessed structure having a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure gradually receding inward from the first surface to the second surface, each V-shaped structure comprising two interconnected ramp surfaces; step S3, depositing a bandpass filter film on at least two ramp surfaces of the V-shaped structure; wherein the execution order of steps S1 and S2 is interchangeable.

[0019] According to a third aspect of this disclosure, a lithography system is provided, including the off-axis illumination lithography mask described above; the lithography system is a proximity lithography system or a projection lithography system, and the light source wavelength range of the lithography system is 157nm~450nm.

[0020] In some exemplary embodiments, when the lithography system is a proximity lithography system, the gap between the lithographic mask and the lithographic substrate is 0 to 120 nm; the gap is filled with air, water or a high refractive index liquid with a refractive index of 1.3 to 1.6.

[0021] (III) Beneficial Effects

[0022] As can be seen from the above technical solutions, the off-axis illumination lithography mask and its preparation method, as well as the lithography system provided in this disclosure, have at least the following beneficial effects:

[0023] (1) By converting vertical illumination to high-angle off-axis illumination through a V-shaped structure, the numerical aperture of the illumination system is increased to 0.8-1.5. This off-axis illumination method effectively suppresses the interference of 0th-order diffraction light and significantly improves the imaging contrast and image edge sharpness. Experimental data show that compared with the traditional vertical illumination method, this disclosure can improve the imaging contrast by 40%-60%, laying a solid foundation for achieving more refined image processing.

[0024] (2) Through different structural designs, this disclosure can realize a variety of lighting modes. A transverse triangular prism structure with a one-dimensional grating arrangement can realize a two-electrode lighting mode, a two-dimensional array structure of an inverted square pyramid can realize a four-electrode lighting mode, and a two-dimensional array structure of an inverted cone can realize a ring lighting mode. This flexible design enables the system to select the optimal lighting mode according to different graphic features, thereby improving process adaptability and application range.

[0025] (3) By integrating the off-axis illumination function into the mask itself, the complex optical components in traditional off-axis illumination systems are effectively simplified. Compared with traditional solutions, this disclosure avoids expensive high-refractive-index prisms and complex optical path adjustment mechanisms, and can be fabricated using conventional micro-nano fabrication processes, which significantly reduces the system manufacturing and maintenance costs.

[0026] (4) The design of the bandpass filter film enables the system to reflect more than 90% of vertically incident light, effectively reducing energy loss. At the same time, it maintains more than 80% transmittance for obliquely incident light that meets the transmission conditions, ensuring full utilization of illumination energy. Actual tests show that compared with the traditional diffraction grating scheme, the energy utilization rate of this disclosure can be improved by about 30%.

[0027] (5) Standard micro-nano fabrication processes are adopted, including photolithography, etching, and thin film deposition, which are fully compatible with existing semiconductor processes. During the manufacturing process, the angle control accuracy of the V-shaped structure can reach ±1°, and the size control accuracy can reach ±50nm, ensuring batch-to-batch consistency. The film thickness control accuracy reaches ±2nm, ensuring the long-term stability of optical performance.

[0028] (6) It is suitable for a variety of lithography light sources in the 157nm-450nm wavelength range, including i-line, KrF, ArF, etc. It can be used in both proximity lithography systems and projection lithography system architectures. In addition, the system supports a variety of working environments such as air, water and high refractive index liquids, showing good application adaptability.

[0029] (7) Off-axis illumination effectively increases the depth of focus and improves process tolerance. The system illumination uniformity is greater than 90%, ensuring consistent pattern quality across the entire exposure area. These characteristics enable the system to support smaller feature size processing, providing a reliable guarantee for the continuous downward extension of technology nodes. Attached Figure Description

[0030] 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:

[0031] Figure 1 A schematic diagram of the structure of an off-axis illumination lithography mask according to an embodiment of the present disclosure is shown.

[0032] Figure 2 The schematic diagram illustrates the structure of the light-incident unit 3 on the first surface of a photolithographic mask according to an embodiment of the present disclosure, wherein, Figure 2 (a) is a schematic diagram of a structure in which the concave structure is a transverse triangular prism structure and arranged in a one-dimensional grating; Figure 2 (b) is a schematic diagram of a structure with a concave structure that is an inverted quadrangular pyramid arranged in a two-dimensional array; and Figure 2 (c) is a schematic diagram of a structure in which the concave structure is an inverted cone structure arranged in a two-dimensional array;

[0033] Figure 3 A schematic flowchart illustrating a method for fabricating an off-axis illumination lithography mask according to an embodiment of the present disclosure is shown; and

[0034] Figure 4 The diagram illustrates a structural schematic of the fabrication process of an off-axis illumination lithography mask according to an embodiment of the present disclosure.

[0035] Figure label:

[0036] 1-Mask substrate, 2-Photolithographic mask pattern structure, 3-Incident light unit, 4-Left slope of V-shaped structure, 5-Right slope of V-shaped structure, 6-Bandpass filter film, 7-Vertical illumination light, 8-Reflected light from the left slope, 9-Reflected light from the right slope, 10-High numerical aperture illumination light incident from the left, 11-High numerical aperture illumination light incident from the right. Detailed Implementation

[0037] 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.

[0038] Figure 1 A schematic diagram of the structure of an off-axis illumination lithography mask according to an embodiment of the present disclosure is shown.

[0039] like Figure 1As shown, the off-axis illumination lithography mask according to an embodiment of this disclosure includes: a mask substrate 1, including a first surface and a second surface disposed opposite to each other; a lithography mask pattern structure 2, located on the second surface of the mask substrate 1; a light-incident portion, located on the first surface of the mask substrate 1, the light-incident portion including a plurality of periodically arranged light-incident units 3; wherein, the light-incident unit 3 includes a recessed structure, the recessed structure having a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure gradually shrinking inward from the first surface to the second surface, each V-shaped structure including two interconnected ramp surfaces; the light-incident portion further includes a bandpass filter film 6, the bandpass filter film 6 at least covering the ramp surfaces of the V-shaped structure.

[0040] In the embodiments of this disclosure, the light incident portion is configured to: reflect illumination light perpendicularly incident on the first surface of the mask substrate 1 through a bandpass filter 6 on one side of the ramp surface to the opposite ramp surface, and transmit the light into the mask substrate 1 when the incident angle satisfies the transmission condition of the bandpass filter 6, forming an off-axis illumination beam. The angle between the ramp of the V-shaped structure and the vertically incident illumination light plays a crucial role in the angle of the incident light. Optionally, the angle α between the normal direction of the ramp surface of the V-shaped structure and the direction of the vertically incident illumination light is 45° to 75° (or the angle β between the ramp surface of the V-shaped structure and the first surface of the photolithography mask is 45° to 75°); the opening size a of the V-shaped structure on the first surface is 500 nm to 1 mm, and the arrangement period b of the V-shaped structure on the first surface can be 500 nm to 1 mm, or slightly larger. By controlling the angle between the ramp surface of the V-shaped structure and the first surface of the mask substrate 1 within the range of 45° to 75°, it is ensured that incident light perpendicular to the first surface of the mask substrate 1 is reflected to form an inclined beam with a high numerical aperture. This angle range balances reflection efficiency and transmission angle requirements, and is a key structural parameter for achieving high-quality off-axis illumination.

[0041] In some exemplary embodiments, the light-incident unit 3 has a recessed structure formed on the first surface of the mask substrate 1. The recessed structure includes a transverse triangular prism structure, an inverted quadrangular pyramid structure, or an inverted cone structure.

[0042] Figure 2 The schematic diagram illustrates the structure of the light incident unit 3 on the first surface of a photomask according to an embodiment of the present disclosure.

[0043] like Figure 2 As shown, when the recessed structure is a transverse triangular prism structure and arranged in a one-dimensional grating, the incident light portion can form a two-electrode illumination. (See [reference]). Figure 2 (a) In this context, when the recessed structure is an inverted square pyramid structure arranged in a two-dimensional array, the incident light portion can form quadrupole illumination; see also (a). Figure 2 (b) In this context, when the recessed structure is an inverted cone structure and arranged in a two-dimensional array, the incident light portion can form ring illumination. See also:Figure 2 (c) in the middle.

[0044] like Figure 2 As shown in (a), the concave structure is a transverse triangular prism structure and is arranged in a one-dimensional grating. When the first surface of the photomask is vertically illuminated, the illumination light illuminating the bandpass filter 6 on one side of the slope of the transverse triangular prism structure cannot pass through or passes very little through the bandpass filter 6 because the incident angle of the vertically illuminated light is not at the transmission window of the bandpass filter 6. However, the vertically illuminated light can be reflected by the bandpass filter 6 to generate reflected light with its propagation direction tilted towards the first and second surfaces of the photomask. This reflected light is incident on the slope on the other side of the transverse triangular prism structure. The incident angle of this reflected light on the slope on the other side of the transverse triangular prism structure is at the transmission window of the bandpass filter 6, and it can pass through the bandpass filter 6 on the opposite slope into the photomask, becoming high numerical aperture illumination. Similarly, the illumination light vertically illuminated by the bandpass filter 6 on the opposite slope of the transverse triangular prism structure is reflected and incident on the bandpass filter 6 on this side of the slope into the photomask, realizing high numerical aperture diode illumination. Optionally, the length c of the transverse triangular prism structure perpendicular to the one-dimensional grating arrangement direction on the first surface can be 0.001mm to 300mm.

[0045] like Figure 2 As shown in (b), the photolithography mask includes multiple periodically arranged inverted quadrangular pyramid structures. These two-dimensional inverted quadrangular pyramid structures are an extension and expansion of the one-dimensional transverse triangular prism structure in a plane. Their core function is to achieve quadrupole illumination, i.e., to form high numerical aperture inclined incident beams from four different directions. From an optical perspective, each inverted quadrangular pyramid structure has a bandpass filter film 6 deposited on its slope surface. When the vertical illumination light 7 is incident on the surface of the inverted quadrangular pyramid structure, reflection and selective transmission occur on each slope surface. Since the structure has inclined surfaces in both two dimensions, the reflected light can propagate in two orthogonal directions and be transmitted into the mask through the bandpass filter film 6 on the opposite slope, thus forming high-angle illumination beams in four directions. This quadrupole illumination method effectively improves imaging contrast and resolution, and is especially suitable for photolithography processes with extremely high requirements for pattern quality and precision. Furthermore, the design of this structure is highly flexible; the period, width, and slope angle of the inverted quadrangular pyramid structure can be adjusted according to actual needs to adapt to the illumination requirements of different pattern areas.

[0046] like Figure 2 As shown in (c), when the recessed structure is an inverted cone structure and arranged in a two-dimensional array, it is used to achieve ring illumination; then, photolithography is performed on the photolithography substrate that is in contact with or close to the photolithography structure through the patterned structure of the second surface of the mask.

[0047] In the embodiments of this disclosure, the light-incident units 3 in different regions of the photolithographic mask can be designed with the same period, width, and slope angle, or light-incident units 3 with different periods, widths, and slope angles can be designed in different regions of the mask to provide the most suitable numerical aperture illumination for different mask pattern structures. This design improves the adaptability of the mask and the uniformity of pattern exposure, and is particularly suitable for complex photolithographic layers containing multiple feature sizes.

[0048] In some exemplary embodiments, the bandpass filter 6 is a Fabry-Perot type interference filter multilayer structure; the bandpass filter 6 is configured to have high reflectivity for illumination light incident perpendicularly to the surface of the bandpass filter 6, and high transmittance for illumination light that has been reflected and incident at a specific tilt angle. Preferably, the high reflectivity is greater than 90%, and the high transmittance is greater than 80%.

[0049] In some exemplary embodiments, the Fabry-Perot interference filter multilayer structure is an all-dielectric type, consisting of alternating stacks of high-refractive-index and low-refractive-index dielectric layers to form a distributed Bragg reflector, with a dielectric resonant cavity layer disposed therein. The high-refractive-index dielectric layer can be made of one or a combination of the following: titanium dioxide, tantalum pentoxide, tantalum trioxide, silicon hydride, silicon nitride, aluminum nitride, and zinc sulfide. The low-refractive-index dielectric layer can be made of one or a combination of the following: silicon dioxide, magnesium fluoride, cryolite, aluminum fluoride, and alumina. The dielectric resonant cavity layer is typically made of a low-absorption, low-refractive-index dielectric to optimize light transmission performance, such as silicon dioxide or magnesium fluoride.

[0050] In some exemplary embodiments, the Fabry-Perot type interference filter multilayer structure is a metal-dielectric hybrid type, comprising two reflective layers made of metallic materials and a dielectric resonant cavity layer sandwiched between the two reflective layers. The material of the metallic reflective layers can be selected from one of the following high-reflectivity metals or their alloys / stacks: aluminum, silver, gold, chromium, molybdenum, tungsten, and titanium. Preferably, for the ultraviolet band, aluminum or chromium can be selected. The material selection for the dielectric resonant cavity layer is similar to that of the all-dielectric type, requiring low absorption, such as silicon dioxide, magnesium fluoride, and aluminum oxide.

[0051] In some exemplary embodiments, the total number of layers in the bandpass filter film 6 is 2 to 100; the thickness of a single layer in the bandpass filter film 6 is 5 nm to 300 nm; and the total thickness of the bandpass filter film 6 is 30 nm to 3000 nm.

[0052] In some exemplary embodiments, the thickness of the mask substrate 1 is 0.01 mm to 10 mm; the material of the mask substrate 1 is a transparent substrate, including one of quartz, glass or sapphire, which not only meets the high transmittance requirements of the ultraviolet to deep ultraviolet band, but also has good thermal stability and mechanical support, and is suitable for high-power lighting and precision exposure scenarios.

[0053] The thickness of the photolithographic mask pattern structure 2 is 50nm to 200nm. The material of the photolithographic mask pattern structure 2 is a non-transparent material, including one of chromium, molybdenum, nickel, germanium or silicon. While ensuring sufficient light-shielding ability and pattern contrast, it avoids the problem of reduced edge steepness or stress accumulation caused by excessive thickness, thereby improving the accuracy and consistency of pattern transfer.

[0054] In the embodiments of this disclosure, the vertically incident light is efficiently converted into a high-angle off-axis illumination beam through the synergistic effect of the incident light unit 3 and the bandpass filter film 6. This structure effectively suppresses zero-order light, enhances the contrast and resolution of the imaging pattern, and is particularly suitable for high-precision lithography processes. The illumination structure is integrated into the first surface of the mask substrate 1, eliminating the need for additional complex off-axis illumination optics. This simplifies the illumination system structure of the lithography equipment, reduces system size and manufacturing costs, and is suitable for various lithography platforms such as proximity, contact, and projection lithography. Utilizing the angular selective transmission characteristics of the bandpass filter film 6, precise control of the incident light direction is achieved, avoiding energy loss, improving illumination efficiency, and facilitating shorter exposure times and increased yield.

[0055] In summary, the solutions of this disclosure, while maintaining the traditional functions of photolithography masks, innovatively integrate off-axis illumination functions into the photolithography mask itself, providing a novel technical path for high numerical aperture lithography that is simple in structure, superior in performance, and feasible in fabrication.

[0056] Figure 3 The schematic diagram illustrates a process flow diagram of a method for fabricating an off-axis illumination lithography mask according to an embodiment of the present disclosure.

[0057] like Figure 3 As shown, the method for fabricating an off-axis illumination lithography mask according to an embodiment of the present disclosure is characterized by comprising steps S1 to S3.

[0058] In step S1, a photolithographic mask pattern structure 2 with a preset pattern is formed on the second surface of the mask substrate 1, see [link to relevant documentation]. Figure 4 (a) in the middle.

[0059] In the embodiments of this disclosure, the thickness of the photomask can be 0.01mm to 10mm; the photomask pattern structure 22 can be a grating, a dot matrix, a marker or other pattern structure.

[0060] In step S2, a light-incident portion comprising a plurality of periodically arranged light-incident units 3 is formed on the first surface of the mask substrate 1; wherein, the light-incident unit 3 includes a recessed structure, the recessed structure having a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure gradually receding inward from the first surface to the second surface, each V-shaped structure including two interconnected ramp surfaces, see [reference needed]. Figure 4(b) in the example; wherein the execution order of steps S1 and S2 can be interchanged.

[0061] In some exemplary embodiments, the method for forming the light-incident unit 3 in step S2 includes: defining a pattern using electron beam lithography or laser direct writing technology, and combining reactive ion etching or wet etching processes to form a V-shaped structure with a slope angle of 45° to 75°.

[0062] In step S3, a bandpass filter film 6 is deposited on at least two sloped surfaces of the V-shaped structure, see [reference]. Figure 4 (c) in the middle.

[0063] In some exemplary embodiments, the method for depositing the bandpass filter film 6 in step S3 includes: employing atomic layer deposition, chemical vapor deposition, or magnetron sputtering techniques; and optimizing the film structure of the bandpass filter film 6 according to the target illumination mode and operating wavelength, including the selection of film material, thickness configuration, and layer number design.

[0064] The photolithographic mask prepared according to the embodiments of this disclosure can be used in a proximity lithography system or a projection lithography system, wherein the light source wavelength range of the lithography system is 157nm~450nm.

[0065] When the lithography system is a proximity or contact lithography system, the gap between the lithography mask and the lithography substrate is 0 to 120 nm; the gap is filled with air, water or a high refractive index liquid with a refractive index of 1.3 to 1.6.

[0066] In embodiments of this disclosure, the lithography system uses an illumination source with a wavelength of 157 nm to 450 nm; an off-axis illumination lithography mask converts vertical illumination into off-axis illumination with a numerical aperture of 0.8 to 1.5; the system also includes an illumination uniformity correction module, which includes diffractive optical elements or microlens arrays, for compensating for the non-uniformity of illumination intensity distribution caused by the periodic arrangement of incident light units 3, ensuring that the illumination uniformity is greater than 90%.

[0067] In the embodiments of this disclosure, by controlling the gap between the photomask and the photolithographic substrate, the mask pattern structure is brought into close proximity or contact with the photolithographic substrate, thereby achieving high-quality exposure of the photolithographic substrate. This high numerical aperture illumination photolithographic mask is suitable not only for proximity lithography but also for projection lithography systems. In projection lithography, this structure can significantly simplify the design of off-axis illumination devices, reduce the overall size of the lithography machine, and improve system integration and process adaptability. Regarding the illumination method, a vertical illumination design is adopted, meaning the illumination light is incident perpendicular to the first and second surfaces of the photomask. The core principle of the high numerical aperture illumination structure is as follows: When vertically incident illumination light strikes the bandpass filter 6 on the slope of the V-shaped structure, it is reflected because the incident angle is not within the transmission window of that side film, forming obliquely propagating reflected light. This reflected light further strikes the bandpass filter 6 on the opposite slope of the V-shaped structure. Since the incident angle is now within the transmission window range of that side film, the light can penetrate into the mask, thereby converting the vertical illumination into high numerical aperture diode, quadrupole, or ring illumination, effectively improving imaging contrast and image resolution. See [link to relevant documentation]. Figure 4 (d) In addition, the fabrication sequence of the photolithographic mask pattern structure 2 has process flexibility. Its fabrication can be completed before the fabrication of the light-incident unit 3 and the bandpass filter film 6 on the first surface of the photolithographic mask, or it can be carried out after the above structure is fabricated. This allows for flexible arrangement of the manufacturing process according to actual process conditions and equipment configuration, thereby improving fabrication efficiency and compatibility.

[0068] Example 1:

[0069] A photolithographic mask pattern structure 2 is fabricated on the second surface of a photolithographic mask. The substrate type is quartz, and the photolithographic mask thickness is 6.25 mm. The photolithographic mask pattern structure 2 is a grating pattern made of chromium. Specifically, electron beam lithography (EBL) is used to form the pattern structure on the second surface of the photolithographic mask. Subsequently, through development, etching, and other process steps, the designed grating structure is precisely transferred onto the mask substrate 1, thereby obtaining the desired photolithographic mask pattern structure 2.

[0070] An incident light unit 3 is fabricated on the first surface of a photomask. The incident light unit 3 is arranged in a one-dimensional grating, and the angle between the ramp normal of the corresponding V-shaped structure and the vertical illumination light 7 is 50°. The incident light unit 3 has a width of 1 μm, a period of 5 μm, and a length of 1 mm in the horizontal direction. Specifically, the fabrication of the incident light unit 3 can be achieved through the following process: first, photoresist is spin-coated on the first surface of the photomask, and the corresponding pattern is formed by direct electron beam writing; then, reactive ion etching (RIE) is used to etch the substrate to obtain the ramp structure with the designed angle.

[0071] A bandpass filter film 6 is deposited on the first surface of the photolithographic mask and the slope of the incident light unit 3. Specifically, the bandpass filter film 6 is an alternating Al / SiO2 film layer, and the bandpass filter film 6 is prepared by chemical vapor deposition (CVD). The prepared bandpass filter film 6 has 10 layers, with a single layer thickness of 20 nm and a total film thickness of 200 nm.

[0072] The prepared photolithography mask is assembled into a proximity lithography system. The bandpass filter film 6 on the first surface of the mask faces the incident light direction and maintains a 30 nm gap with the photolithography substrate. An i-line light source with a wavelength of 365 nm is selected as the light source. When the illumination light is incident perpendicularly on the first surface of the mask, part of the light is reflected by the bandpass filter film 6 on the slope of the V-shaped structure, forming reflected light 8 on the left slope and reflected light 9 on the right slope, which propagate at an angle. This reflected light is then incident on the opposite slope of the V-shaped structure. The reflected light 8 on the left slope is incident on the right slope 5 of the V-shaped structure, and the reflected light 9 on the right slope is incident on the left slope 4 of the V-shaped structure. When the incident angle is within the bandpass window range, it passes through the bandpass filter film 6 and enters the mask substrate 1, thereby realizing the high numerical aperture secondary illumination light with angled incidence, including the high numerical aperture illumination light 10 incident on the left and the high numerical aperture illumination light 11 incident on the right.

[0073] Example 2:

[0074] An incident light unit 3 is fabricated on the first surface of a photomask. The incident light unit 3 is arranged in a one-dimensional grating, with the angle between the ramp normal and the vertical illumination light 7 being 60°. The incident light unit 3 has a width of 5 μm, a period of 10 μm, and a length of 10 mm in the horizontal direction. Specifically, the fabrication of the incident light unit 3 can be achieved through the following process: first, photoresist is spin-coated on the first surface of the photomask, and the corresponding pattern is formed by laser direct writing; then, the substrate is etched using an inductively coupled plasma (ICP) etching method to obtain the ramp structure with the designed angle.

[0075] A bandpass filter film 6 is deposited on the first surface of the photolithographic mask and the slope of the incident light unit 3. Specifically, the bandpass filter film 6 is an alternating Ag / Al2O3 film layer, and the bandpass filter film 6 is prepared by physical vapor deposition (PVD). The prepared bandpass filter film 6 has 20 layers, with a single layer thickness of 30 nm and a total film thickness of 600 nm.

[0076] A photolithographic mask pattern structure 2 is fabricated on the second surface of a photolithographic mask. The substrate type is glass, and the photolithographic mask thickness is 10 mm. The photolithographic mask pattern structure 2 is a dot matrix pattern made of chromium. Specifically, an EBL (Extended Brush Laser) is used to form the pattern structure on the second surface of the photolithographic mask. Subsequently, through development, etching, and other process steps, the designed grating structure is precisely transferred onto the mask substrate 1, thereby obtaining the desired photolithographic mask pattern structure 2.

[0077] The prepared photolithography mask is assembled into a proximity lithography system. The bandpass filter film 6 on the first surface of the mask faces the incident light direction and maintains a 10 nm gap with the photolithography substrate. An ArF light source with a wavelength of 193 nm is selected as the light source. Water is injected between the mask substrate 1 and the photolithography substrate to further improve the light coupling efficiency and resolution. When the illumination light is incident perpendicularly on the first surface of the mask, part of the light is reflected by the bandpass filter film 6 on the V-shaped structure slope, forming reflected light 8 on the left slope and reflected light 9 on the right slope, which propagate at an angle. This reflected light is then incident on the opposite slope of the V-shaped structure, where the reflected light 8 on the left slope is incident on the right slope 5 of the V-shaped structure and the reflected light 9 on the right slope is incident on the left slope 4 of the V-shaped structure. When the incident angle is within the bandpass window range, it passes through the film layer into the mask substrate 1, thereby realizing the high numerical aperture secondary illumination light with angled incident, including the high numerical aperture illumination light 10 incident on the left and the high numerical aperture illumination light 11 incident on the right.

[0078] Example 3:

[0079] A photolithographic mask pattern structure 2 is fabricated on the second surface of a photolithographic mask. The substrate type is sapphire, and the photolithographic mask thickness is 5 mm. The photolithographic mask pattern structure 2 is a marker pattern made of silicon. Specifically, the pattern structure is formed on the second surface of the photolithographic mask using nanoimprint lithography (NIL) technology. Subsequently, through development, etching, and other process steps, the designed grating structure is precisely transferred onto the mask substrate 1, thereby obtaining the desired photolithographic mask pattern structure 2.

[0080] An incident light unit 3 is fabricated on the first surface of a photomask. The incident light unit 3 is arranged in a two-dimensional inverted pyramid structure, with the angle between the ramp normal and the vertical illumination light 7 being 70°. The incident light unit 3 has a width of 5 μm, a period of 20 μm, and a length of 0.5 mm in the horizontal direction. Specifically, the incident light unit 3 is fabricated through the following process: first, photoresist is spin-coated onto the first surface of the photomask, and the corresponding pattern is formed using NIL (Non-Inductively Coupled Irradiation); then, wet etching is used to etch the substrate to obtain the ramp structure with the designed angle.

[0081] A bandpass filter film 6 was deposited on the first surface of the photolithographic mask and the slope of the V-shaped structure. Specifically, the bandpass filter film 6 is an alternating SiO2 / Al2O3 film layer, and the bandpass filter film 6 was prepared by magnetron sputtering. The prepared bandpass filter film 6 has 30 layers, with a single layer thickness of 10 nm and a total film thickness of 300 nm.

[0082] The prepared photolithography mask is assembled into a projection lithography system. The mask is placed on the mask stage of the projection lithography machine, and the depth of focus is controlled by a precision focusing system to ensure that the bandpass filter structure is located within the incident light focal plane. The bandpass filter film 6 on the first surface of the mask faces the incident light direction. A KrF light source with a wavelength of 248 nm is selected as the light source. When the illumination light is incident perpendicularly to the first surface of the mask, part of the light is reflected by the bandpass filter film 6 on the V-shaped structure slope, forming reflected light 8 on the left slope and reflected light 9 on the right slope, which propagate at an angle. This reflected light is then incident on the opposite slope of the V-shaped structure. The reflected light 8 on the left slope is incident on the right slope 5 of the V-shaped structure, and the reflected light 9 on the right slope is incident on the left slope 4 of the V-shaped structure. When the incident angle is within the bandpass window range, the light passes through the film layer and enters the mask substrate 1, thereby realizing the high numerical aperture fourth-order illumination light with angled incidence, including the high numerical aperture illumination light 10 incident on the left and the high numerical aperture illumination light 11 incident on the right.

[0083] 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. An off-axis illumination photolithography mask, characterized in that, The application relates to a mask substrate, which comprises a first surface and a second surface arranged oppositely; a photolithography mask pattern structure is arranged on the second surface of the mask substrate; and a light inlet part is arranged on the first surface of the mask substrate, wherein the light inlet part comprises a plurality of periodically arranged light inlet units; the light inlet unit comprises a recess structure, the recess structure has a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure is gradually inwardly tapered in a direction from the first surface to the second surface, and each V-shaped structure comprises two mutually connected slope surfaces; and the light inlet part further comprises a band-pass filter film which covers at least the two slope surfaces of the V-shaped structure. The recess structure comprises a transverse triangular prism structure, an inverted quadrangular pyramid structure or an inverted circular cone structure.

3. The off-axis illumination photolithography mask according to claim 2, wherein when the recess structure is a transverse triangular prism structure and arranged in a one-dimensional grating, the light inlet part can form two-pole illumination; when the recess structure is an inverted quadrangular pyramid structure and arranged in a two-dimensional array, the light inlet part can form four-pole illumination; and when the recess structure is an inverted circular cone structure and arranged in a two-dimensional array, the light inlet part can form ring illumination. The band-pass filter film is a Fabry-Perot type interference filter multilayer structure. The band-pass filter film is configured to have high reflectivity for illumination light which is normally incident to the surface of the band-pass filter film and high transmissivity for illumination light which is incident at a specific oblique angle after being reflected. The Fabry-Perot type interference filter multilayer structure is a full dielectric type, which comprises a distributed Bragg reflector formed by alternately stacking high refractive index dielectric layers and low refractive index dielectric layers and a dielectric resonant cavity layer arranged in the distributed Bragg reflector.

2. The off-axis illumination lithography mask of claim 1, wherein, The Fabry-Perot type interference filter multilayer structure is a metal-dielectric hybrid type, which comprises two reflection layers composed of metal materials and a dielectric resonant cavity layer arranged between the two reflection layers. The angle between the normal line of the slope surface of the V-shaped structure and the direction of the illumination light which is normally incident to the first surface of the mask substrate is 45-75 degrees. The total number of film layers of the band-pass filter film is 2-100. The thickness of a single film layer in the band-pass filter film is 5-300 nm. The total thickness of the band-pass filter film is 30-3000 nm.

4. The off-axis illumination lithography mask of claim 1, wherein, The application further relates to a method for manufacturing the mask substrate, which comprises the following steps: S1, forming a photolithography mask pattern structure with a preset pattern on the second surface of the mask substrate; S2, forming a light inlet part comprising a plurality of periodically arranged light inlet units on the first surface of the mask substrate, wherein the light inlet unit comprises a recess structure which has a V-shaped structure in a direction perpendicular to the first surface, the V-shaped structure is gradually inwardly tapered in a direction from the first surface to the second surface, and each V-shaped structure comprises two mutually connected slope surfaces; S3, depositing a band-pass filter film on at least the two slope surfaces of the V-shaped structure; and the execution sequence of steps S1 and S2 can be interchanged. The application further relates to a mask substrate manufacturing system, which comprises the off-axis illumination photolithography mask according to any one of claims 1-8.

5. The off-axis illumination lithography mask of claim 4, wherein, ​ 6. The off-axis illumination lithography mask of claim 4, wherein, ​ 7. The off-axis illumination lithography mask of claim 1, wherein, ​ 8. The off-axis illumination lithography mask of claim 4, wherein, ​ ​ ​ 9. A method of making an off-axis illumination lithography mask according to any one of claims 1 to 8, characterized in that, ​ ​ ​ ​ ​ 10. A lithographic system, characterized by, ​ The photolithography system is a proximity contact photolithography system or a projection photolithography system, and the light source wavelength range of the photolithography system is 157nm-450nm.

11. The photolithography system of claim 10, wherein, When the photolithography system is a proximity contact photolithography system, the gap spacing between the photolithography mask and the photolithography substrate is 0-120nm; the gap is filled with air, water or a high refractive index liquid with a refractive index of 1.3-1.6.

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