Deep ultraviolet microscope objective

Abstract

The utility model relates to a kind of deep ultraviolet microscopes objective, including the first lens group G1, second lens group G2, third lens group G3 and optical observation window mirror C1 being sequentially arranged along the direction of image side to object side;The first lens group G1 is weak negative power, is made of one or more negative meniscus lens, and the equivalent focal length range is-10mm to-30mm;The second lens group G2 is weak positive power, is made of one or more positive and negative alternate lens, and the equivalent focal length range is 50mm to 100mm;The third lens group G3 is strong positive power, is made of one or more meniscus lens, and the equivalent focal length range is 10mm to 25mm;The optical observation window mirror C1 two sides are parallel and perpendicular to optical axis direction.The utility model has single material construction, high numerical aperture, long working distance and has window thickness self-adapting compensation ability.

Description

Technical Field

[0001] In the field of automated optical inspection of semiconductors, particularly a deep ultraviolet microscope objective. Background Technology

[0002] As semiconductor manufacturing processes advance to nodes of 28nm and below, the precision requirements for mask or wafer defect detection have entered the 20-30nm level. Traditional visible light microscopes can no longer meet these precision requirements. Ultraviolet (UV) microscopy systems, due to their shorter wavelengths, can achieve higher resolution and have become the industry's preferred choice. Semiconductor mask defect detection equipment places three stringent requirements on deep UV microscope objectives: first, to overcome the resolution bottleneck and improve photon collection efficiency, the numerical aperture of the objective must be increased; second, the objective needs a long working distance to avoid collision with the mask's protective coating layer (approximately 6mm thick); and third, to improve detection efficiency, the objective needs to meet a large field of view.

[0003] However, existing technologies present significant contradictions: 1. It is difficult to achieve both high numerical aperture and long working distance: As patents CN114002815A and CN116256878A point out, traditional high-magnification (f≤5mm) objectives typically require sacrificing working distance (WD<4mm) to achieve high numerical aperture (NA>0.8). Short working distance objectives are prone to mask collision risks; while in currently available information, long working distance designs (such as WD=15mm in CN116449550A) only achieve NA=0.7, and the resolution cannot meet the requirements of advanced processes. 2. The complexity of processes introduced by multiple materials: Existing deep ultraviolet objective designs (such as CN119667902A) rely on multiple special optical glasses to correct aberrations, resulting in high material costs and complex coating processes. 3. Aberration compensation challenge: Mask detection requires penetrating the protective film layer, and the spherical aberration and field curvature introduced by the thick window need to be dynamically compensated by the objective lens. However, existing objectives lack adaptive correction capabilities (such as CN114002815A, which attempts to compensate for the window thickness by moving the lens group, but the structure is complex).

[0004] Therefore, there is an urgent need to develop a transmission-type deep ultraviolet microscope objective with a single material, high numerical aperture, long working distance, and adaptive window thickness to meet the mass production inspection requirements of semiconductor photomasks. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide a deep ultraviolet microscope objective lens that is constructed of a single material, has a high numerical aperture, a long working distance, and has the ability to adaptively compensate for window thickness.

[0006] The technical solution of this utility model to solve the above-mentioned technical problems is as follows: A deep ultraviolet microscope objective includes a first lens group G1, a second lens group G2, a third lens group G3, and an optical observation window lens C1 arranged sequentially along the image-to-object direction. The first lens group G1 is a weak negative optical power, consisting of one or more negative meniscus lenses, with an equivalent focal length range of -10mm to -30mm; The second lens group G2 is a weak positive power lens, consisting of one or more alternating positive and negative lenses, with an equivalent focal length range of 50mm to 100mm. The third lens group G3 is a strong positive optical power, consisting of one or more meniscus lenses, with an equivalent focal length range of 10mm to 25mm. The optical observation window mirror C1 has two parallel surfaces that are perpendicular to the optical axis.

[0007] The beneficial effects of this invention are as follows: The first lens group G1, composed of one or more negative meniscus lenses, forms a weak negative optical power group (equivalent focal length -10mm to -30mm). Its primary function is to prevent light from prematurely converging at a high degree. It allows the light beam to enter the subsequent lens group in a more "gentle" manner, laying the foundation for controlling telecentricity. In addition, because telecentricity requires the angle between the principal ray and the optical axis to be as small as possible, the first lens group G1, through its diverging characteristics, can also effectively control the exit angle of the edge rays, keeping the principal ray parallel to the optical axis, satisfying the image-side telecentricity condition, thereby constraining the field curvature and image-side telecentricity of the overall lens, ensuring a flat image plane in a large field of view, and meeting the high-precision detection requirements of the entire area of ​​semiconductor masks.

[0008] The second lens group G2, as a mid-range weak positive focal length lens group, plays a crucial role in finely correcting aberrations and supporting the high numerical aperture performance of the third lens group G3, which has a strong positive focal length. While the third lens group G3 significantly improves the numerical aperture to collect large-angle light, it introduces severe higher-order aberrations such as spherical aberration and coma, leading to blurred images. Each positive and negative lens in the second lens group G2 can be considered a "correction unit" used to balance specific aberrations (such as spherical aberration and coma). One or more lenses mean one or more such correction units that perform extremely fine and thorough correction of remaining aberrations (especially higher-order aberrations and chromatic aberrations not fully corrected by the first lens group G1). Distortion is closely related to the propagation path of the principal ray; the second lens group G2, with its multiple lenses, provides a large number of variables controlling the angle of the principal ray. Through symmetrical or near-symmetrical optical design and in combination with the position of the aperture stop, the second lens group G2 can ensure that the principal rays of different fields of view satisfy the object-image conjugate relationship, thereby reducing optical distortion to an extremely low level. The curvature combination of different lenses can be used to generate reverse aberrations to specifically cancel the spherical aberration and coma introduced by the third lens group G3, ensuring that the overall aberration of the system is at a low level and effectively improving imaging clarity and contrast.

[0009] Furthermore, although the first lens group G1, the second lens group G2, and the third lens group G3 perform different functions—the first lens group G1 (controller) is responsible for managing light and preprocessing aberrations, the second lens group G2 (corrector & imager) is responsible for providing the main optical power and aberration balance, and the third lens group G3 is responsible for increasing the numerical aperture to collect large-angle light—it is precisely this unique division of labor that allows the aberration correction task to be distributed across the three lens groups of the entire system, rather than just on the last few lenses. This results in a better global aberration balance effect. With more lenses and a more balanced distribution of optical power, the system is less sensitive to manufacturing errors (such as small deviations in thickness and spacing) and environmental changes (such as temperature fluctuations), making the system more stable, or more "adaptable."

[0010] Furthermore, by dispersing the pressure through the coordinated division of labor and aberration balance of the three lens groups, both performance and efficiency can be achieved. At the same time, the addition of a non-optical power correction plate (an optical observation window mirror C1 with two parallel surfaces and perpendicular to the optical axis) refracts the large-angle refracted light on the object side from both sides, making the outgoing light closer to the principal optical axis and reducing the output aperture. Thus, within the limited aperture, the field of view of the system is expanded.

[0011] Based on the above technical solution, the present invention can be further improved as follows.

[0012] Furthermore, the first lens group G1 preferably contains three negative meniscus lenses, which are labeled L1 to L3 from the image side to the object side. The surface S1 of lens L1 facing the image side is concave, and the surface S2 facing the object side is concave. The surface S3 of lens L2 facing the image side is concave, and the surface S4 facing the object side is concave. The surface S5 of lens L3 facing the image side is concave, and the surface S6 facing the object side is concave.

[0013] The beneficial effects of adopting the above-mentioned further solution are as follows: Lenses L1 to L3 all adopt a "double-sided concave surface" design. By matching the curvature of the double-sided concave surfaces, the refraction paths of light rays at the edges of different fields of view can be precisely controlled, ensuring that the principal ray always remains parallel to the optical axis and satisfies the image-side telecentric condition. This characteristic can avoid imaging shift caused by image plane displacement and improve the alignment accuracy in semiconductor mask inspection.

[0014] In addition, the double-concave structure helps to enhance the ability to converge light rays at the edge of the field of view, thereby improving the field curvature and astigmatism of the system, making the imaging surface flatter, and improving the consistency of the overall imaging quality.

[0015] Furthermore, the radius of curvature of surface S1 of lens L1 is -261mm to -262mm, and the radius of curvature of surface S2 is 27mm to 28mm; the radius of curvature of surface S3 of lens L2 is -61mm to -62mm, and the radius of curvature of surface S4 is 55mm to 56mm; the radius of curvature of surface S5 of lens L3 is -173mm to -174mm, and the radius of curvature of surface S6 is 37mm to 38mm.

[0016] The beneficial effects of adopting the above-mentioned further scheme are as follows: Surfaces S1, S3, and S5 in lenses L1~L3 are all concave surfaces with large radii of curvature, while surfaces S2, S4, and S6 are all concave surfaces with small radii of curvature. This effectively ensures that the overall equivalent focal length of the first lens group G1 is stable within the weak negative power range of -10mm to -30mm. Therefore, it can both prevent premature convergence of light and provide appropriate pre-processing for light divergence in subsequent lens groups. Furthermore, by matching the large radii of curvature (gentle concave surfaces) of surfaces S1, S3, and S5 with the small radii of curvature (steep concave surfaces) of surfaces S2, S4, and S6, the refraction angle of the edge light can be precisely adjusted, keeping the angle between the principal ray and the optical axis within a very small range (meeting the image-side telecentric requirement), thus improving the alignment stability in semiconductor detection.

[0017] Meanwhile, the double-concave design in lenses L1 to L3 can also "grade diverge" light through curvature gradient (such as the gradual change of the concave curvature radius of lenses L1 to L3), which can suppress some spherical aberration and coma in advance, reduce the aberration correction pressure of the second lens group G2, and thus improve the imaging clarity and uniformity of the overall system.

[0018] Furthermore, by finely optimizing the radius of curvature, chromatic aberration can be suppressed for light of different wavelengths, further enhancing the applicability of the system in multispectral detection scenarios. This design not only improves the functionality and adaptability of the optical system, but also provides a more reliable optical solution for high-precision optical inspection equipment.

[0019] Furthermore, the second lens group G2 preferably contains eight alternating positive and negative lenses, labeled L12 to L15 sequentially from the image side to the object side. Lens L4 has a concave surface S7 facing the image side and a convex surface S8 facing the object side; lens L5 has a convex surface S9 facing the image side and a concave surface S10 facing the object side; lens L6 has a convex surface S11 facing the image side and a convex surface S12 facing the object side; lens L7 has a concave surface S11 facing the image side and a convex surface S12 facing the object side; and lens L7 has a concave surface S11 facing the image side and a convex surface S12 facing the object side. S13 is a concave surface, and S14, the object-facing surface, is a convex surface; S15, the image-facing surface of lens L8, is a convex surface, and S16, the object-facing surface, is a convex surface; S17, the image-facing surface of lens L9, is a concave surface, and S18, the object-facing surface, is a convex surface; S19, the image-facing surface of lens L10, is a convex surface, and S20, the object-facing surface, is a convex surface; S21, the image-facing surface of lens L11, is a convex surface, and S22, the object-facing surface, is a convex surface.

[0020] The beneficial effects of adopting the above-mentioned further scheme are as follows: The combination of concave and convex surfaces in lenses L4-L11 enables efficient light convergence and aberration balance. Specifically, the combination of concave and convex surfaces effectively corrects spherical and coma aberrations and improves the uniformity of the beam incident on the image plane, thereby enhancing the system's imaging quality. Simultaneously, the concave or convex surface designs facing the image side, such as surfaces S7, S9, and S11, can work synergistically with the divergence characteristics of the first lens group G1 to further optimize light distribution, meeting the stringent requirements for high resolution and high contrast in semiconductor inspection. Furthermore, by rationally allocating the curvature radius and thickness of each lens, the overall length and magnification of the system can be effectively controlled, achieving a good balance between compactness and performance in the optical system. Moreover, this design helps suppress stray light generation, improves the optical system's anti-interference capability and signal-to-noise ratio, thereby further enhancing detection accuracy and stability, effectively meeting the stringent requirements of high-density, high-precision semiconductor manufacturing and inspection scenarios for optical systems.

[0021] Furthermore, the radius of curvature of surface S7 of lens L4 is -239mm to -240mm, and the radius of curvature of surface S8 is -50mm to -51mm; the radius of curvature of surface S9 of lens L5 is 68mm to 69mm, and the radius of curvature of surface S10 is 35mm to 36mm; the radius of curvature of surface S11 of lens L6 is 122mm to 123mm, and the radius of curvature of surface S12 is -73mm to -74mm; the radius of curvature of surface S13 of lens L7 is -37mm to -38mm, and the radius of curvature of surface S14 is -77mm to -78mm; lens L8... The radius of curvature of surface S15 is 153mm to 154mm, and that of surface S16 is -108mm to -109mm; the radius of curvature of surface S17 of lens L9 is -31mm to -32mm, and that of surface S18 is -41mm to -42mm; the radius of curvature of surface S19 of lens L10 is 1184mm to 1185mm, and that of surface S20 is -74mm to -75mm; the radius of curvature of surface S21 of lens L11 is 567mm to 568mm, and that of surface S22 is -120mm to -121mm.

[0022] The beneficial effects of adopting the above-mentioned further scheme are as follows: the curvature radii of each surface of lenses L4 to L11 are precisely designed, which can effectively correct spherical aberration and coma over a wide wavelength range. For example, lens L4 (concave-convex surface, S7=-239mm to -240mm / S8=-50mm to -51mm) is a positive optical power unit, and its convex surface (S8) can converge light but introduce positive spherical aberration; the subsequent lens L5 (convex-concave surface, S9=68mm to 69mm / S10=35mm to 36mm) is a negative optical power unit, and its concave surface (S10) diverges light and generates negative spherical aberration. The two form a "positive spherical aberration - negative spherical aberration" cancellation pair, which effectively reduces the total spherical aberration and thus improves the image quality.

[0023] Lens L6 (convex-convex, S11=122mm to 123mm / S12=-73mm to -74mm) and lens L7 (concave-convex, S13=-37mm to -38mm / S14=-77mm to -78mm) use a combination of curved surfaces of “convex (positive) → concave (negative) → convex (positive)” to cancel out the reverse aberrations (such as positive and negative spherical aberration, positive and negative coma) generated by different curvatures. This accurately corrects the higher-order aberrations introduced by the strong positive optical power of the third lens group G3, ensuring that the system's imaging quality is close to the diffraction limit.

[0024] Lens L8 (convex-concave, S15=153mm to 154mm / S16=-108mm to -109mm) and lens L9 (concave-concave, S17=-31mm to -32mm / S18=-41mm to -42mm) form a negative power combination, significantly reducing the advanced spherical aberration remaining from the previous lens group. The combination of the double concave and convex-concave surfaces further balances astigmatism and field curvature, ensuring consistent image sharpness across the entire field of view. Simultaneously, the strong divergence of the concave surface S17 effectively compresses the beam aperture, providing more compact beam input conditions for subsequent lens group light correction.

[0025] Lens L10 (convex-concave, S19=1184mm to 1185mm / S20=-74mm to -75mm) and lens L11 (convex-concave, S21=567mm to 568mm / S22=-120mm to -121mm) constitute the image-side compensation unit. The convex surface (S19) of lens L10 with its ultra-long radius of curvature greatly reduces the incident angle of light, significantly reducing the generation of higher-order coma. Meanwhile, the concave surface (S22) of lens L11 further refines the convergence of light rays at the edge of the image plane, enabling the image quality to reach the diffraction limit.

[0026] Therefore, by synergistically optimizing the curvature radii of the aforementioned lens surfaces, high-resolution imaging with a wide spectral density and high numerical aperture can be achieved, effectively meeting the application requirements of precision optical inspection and imaging equipment.

[0027] Furthermore, the third lens group G3 contains four meniscus lenses, labeled L12 to L15 from the image side to the object side. Lens L12 has a convex surface S23 facing the image side and a concave surface S24 facing the object side; lens L13 has a convex surface S25 facing the image side and a concave surface S26 facing the object side; lens L14 has a convex surface S27 facing the image side and a concave surface S28 facing the object side; and lens L15 has a convex surface S29 facing the image side and a concave surface S30 facing the object side.

[0028] The beneficial effects of adopting the above-mentioned further scheme are as follows: Lenses L12 to L15 all adopt a positive meniscus lens design with an image-side convex surface and an object-side concave surface. The positive meniscus lens (with a center thickness greater than the edge) can produce stable strong positive optical power through the synergistic effect of convex convergence and concave divergence, significantly improving the system's numerical aperture. Simultaneously, the convex surfaces of all four positive meniscus lenses face the image side, forming a symmetrical light guiding path, ensuring that the main ray remains parallel to the optical axis after passing through the third lens group G3, thus satisfying the image-side telecentric condition together with the first lens group G1 and the second lens group G2. Furthermore, the combination of concave and convex surfaces of the positive meniscus lens can achieve a strong converging effect within a shorter optical length. Combined with the optical observation window lens C1, this allows the system to meet the long working distance while avoiding the risk of collision with the mask protective film layer, complying with the mechanical design constraints of semiconductor testing equipment.

[0029] Furthermore, the radius of curvature of surface S23 of lens L12 is 89mm to 90mm, and surface S24 is flat; the radius of curvature of surface S25 of lens L13 is 42mm to 43mm, and the radius of curvature of surface S26 is 98mm to 99mm; the radius of curvature of surface S27 of lens L14 is 42mm to 43mm, and the radius of curvature of surface S28 is 62mm to 63mm; the radius of curvature of surface S29 of lens L15 is 19mm to 20mm, and the radius of curvature of surface S30 is 46mm to 47mm.

[0030] The beneficial effects of adopting the above-mentioned further scheme are as follows: From the curved surface S23 (89mm to 90mm) of lens L12 to the curved surface S29 (19mm to 20mm) of lens L15, the radius of curvature of the convex surface gradually decreases (curvature increases), forming a gradient change of "gentle convergence → strong convergence", which can efficiently collect large-angle light rays from the object side, thereby improving the numerical aperture. Among them, the curved surface S24 of lens L12 is a plane, which can weaken the optical power contribution of this surface and avoid astigmatism caused by excessive concave curvature; at the same time, the planar design reduces the abrupt refraction of light on this surface, reduces the generation of higher-order aberrations (such as distortion, field curvature), and reserves adjustment margin for the strong curvature correction of subsequent lenses L13~L15; the radius of curvature of the curved surfaces S25 / S27 of lenses L13 and L14 is 42mm to 43mm (convex), forming a symmetrical light guiding structure to ensure that the principal rays of different fields of view remain within the third lens group G3. Maintaining parallelism to the optical axis, the lens works in conjunction with the first lens group G1 and the second lens group G2 to maintain image-side telecentric accuracy and avoid alignment deviations during mask inspection. The curved surface S29 (19mm to 20mm) of lens L15 serves as the exit surface of the last lens in the system. Its strong curvature design further enhances the converging capability, ensuring that a high numerical aperture can be maintained even at long working distances. At the same time, its small radius of curvature effectively compresses the overall length of the optical system, improving the compactness and space utilization of the equipment, and meeting the dual requirements of semiconductor inspection equipment for optical performance and structural layout.

[0031] Furthermore, the negative meniscus lens, the alternating positive and negative lens, and the meniscus lens are all spherical designs.

[0032] The advantages of adopting the above-mentioned further solutions are as follows: the processing of spherical lenses relies on mature spherical grinding and polishing processes. Compared with aspherical lenses, their mold development, processing accuracy control, and inspection methods (such as interferometer inspection) are all simpler, which can significantly reduce the processing cost of deep ultraviolet fused silica material (approximately 40% lower than the aspherical solution). At the same time, the standardized production of spherical curvature is conducive to parameter consistency in mass production, reducing performance fluctuations caused by processing errors and improving the stability of system mass production.

[0033] Furthermore, the negative meniscus lens, the alternating positive and negative lens, and the meniscus lens are all made of deep ultraviolet spectral fused silica lens.

[0034] The advantages of adopting the above-mentioned further scheme are: fused silica has excellent light transmittance (transmittance >95%) in the deep ultraviolet spectral band (266nm), which can reduce light energy loss, ensure photon collection efficiency at high numerical apertures (NA≥0.85), meet the high-sensitivity imaging requirements for 20~30nm defect detection in semiconductor masks, and the single material can effectively avoid chromatic aberration (such as secondary spectral distortion) introduced by the difference in refractive index between different optical glasses, simplifying the difficulty of aberration correction; at the same time, fused silica has a low coefficient of thermal expansion (0.55×10⁻⁶). -6 ( / ℃) Ensures the system's refractive index and dimensional stability under temperature fluctuations (-10~50℃), with image plane drift ≤2nm, which is superior to the thermal mismatch risk of multi-material systems.

[0035] Furthermore, the object-side numerical aperture NA is ≥0.85, and the working wavelength is 266nm.

[0036] The beneficial effects of adopting the above-mentioned further scheme are as follows: By combining a 266nm deep ultraviolet short wavelength with a high numerical aperture (NA) ≥ 0.85, the system's characteristic resolution can be improved to 157nm (measured value in the example), meeting the high-precision detection requirements of 20-30nm defects in semiconductor 28nm and below process masks. This breaks through the performance bottleneck of traditional visible light microscopes (such as 405nm wavelength, with a resolution of approximately 350nm when NA=0.7), thereby overcoming the diffraction limit and achieving high-resolution imaging. The high NA (≥0.85) can also collect large-angle light with an object half-angle ≥ 58°. Combined with the high transmittance (>95%) of fused silica in the 266nm band, it significantly improves photon collection efficiency and enhances detection sensitivity. At the same time, the 266nm wavelength is in the deep ultraviolet "transparent window," and fused silica has no obvious absorption peak in this band, which can reduce light energy loss. Furthermore, the short wavelength reduces the influence of scattering sources such as dust and scratches in the optical system. With the low stray light design of the spherical lens, the system's stray light suppression ratio can reach 10. -6 This design avoids interference from false defect signals and improves detection accuracy. Furthermore, through the collaborative design of the first lens group G1 (weak negative optical power), the second lens group G2 (alternating positive and negative aberration correction), and the third lens group G3 (strong positive optical power gradient convergence), the working distance is increased to ≥7.5mm while achieving an NA ≥0.85. It is also safe to use with a mask protective film layer (approximately 6mm thick), avoiding the risk of collision between the objective lens and the mask during the detection process. This further resolves the contradiction between "high resolution and short working distance" in traditional high NA objectives. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the microscope objective of this utility model; Figure 2 This is an evaluation graph of the modulation transfer function and optical transfer function of the microscope objective of this invention; Figure 3 This is a waveform aberration result within the field of view of the microscope objective of this invention; Figure 4 The images show the field curvature and distortion results of the microscope objectives of this invention. Figure 5 An imaging point diagram of the deep ultraviolet objective optical system provided for an embodiment of this utility model. Detailed Implementation

[0038] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0039] The input parameters of the imaging objective of this invention are as follows: a long working distance plan-field ultraviolet microscope objective with numerical aperture NA = 0.85 and focal length f = 5 mm, working wavelength of 266 nm, compensated optical observation window thickness of D = 4 mm, total objective length ≤ 180 mm, object-side working distance ≥ 7.5 mm, and RMS wavelet aberration ≤ 0.003λ@266 nm (i.e. ≤ 8 nm).

[0040] It should be noted that the working wavelength in this embodiment is specifically selected as 266nm, and it is not only applicable to the sub-wavelength. In the case of 255nm-275nm, with appropriate adjustments based on the structure of this utility model patent, the overall effect of objective lens total length ≤180mm, object-side working distance ≥7.5mm, and RMS wavelet aberration ≤0.003λ@266nm (i.e. ≤8nm) can also be achieved. Therefore, all embodiments with wavelength applicability made under this utility model are within the scope of protection of this utility model.

[0041] like Figure 1 As shown, the microscope consists of a first lens group G1, a second lens group G2, a third lens group G3, and an optical observation window C1, totaling 15 lenses and 1 window mirror, arranged sequentially from image to object. The first lens group G1 has a negative optical power, while the second and third lens groups G3 both have positive optical power. The definition is... Figure 1 The object side is the right side, i.e., the position of the object plane, and the image side is the left side.

[0042] In this embodiment, the first lens group G1 has negative optical power and consists of three negative meniscus lenses, labeled L1~L3, with a combined focal length close to -12.5mm. The negative focal length of the first lens group G1 will generate negative PETS, which can control the edge ray angle (image-side telecentricity) and constrain the overall field curvature and image-side telecentricity of the lens. The second lens group G2 is designed with weak positive optical power and consists of eight alternating positive and negative lenses, labeled L4~L11, with a combined focal length close to 60mm. The third lens group G3 has strong positive optical power and consists of four meniscus lenses, labeled L12~L15, with a combined focal length close to 33mm. The strong positive focal length of the third lens group G3 will result in a high numerical aperture (NA) value, thus collecting light at a wider angle. However, it will produce severe spherical aberration and coma, leading to image blurring. The optimized design of the second lens group G2 can be used to counteract the effects of higher-order aberrations such as spherical aberration and coma.

[0043] The first lens group G1, from image to object along the same optical axis, includes: a lens L1 with negative optical power, a lens L2 with negative optical power, and a lens L3 with negative optical power, with focal lengths of f1 = -50.3 mm, f2 = -57.4 mm, and f3 = 62.0 mm, respectively, satisfying 10 ≤ | |≤13、10≤| |≤13、10≤| | ≤13. The first lens L1 has a concave surface S1 facing the image side and a concave surface S2 facing the object side; the second lens L2 has a concave surface S3 facing the image side and a concave surface S4 facing the object side; the second lens L3 has a concave surface S5 facing the image side and a concave surface S6 facing the object side.

[0044] The second lens group G2, from image side to object side along the same optical axis, includes: lens L4 with positive optical power, lens L5 with negative optical power, lens L6 with positive optical power, lens L7 with negative optical power, lens L8 with positive optical power, lens L9 with negative optical power, lens L10 with positive optical power, and lens L11 with positive optical power. The combined focal length of these eight lenses is fm = 60.8 mm, satisfying 10 ≤ | | ≤13. In the second lens group G2, starting from the image side to the object side, the design of each surface is as follows: the curved surface S7 of lens L4 facing the image side is concave, and the curved surface S8 facing the object side is convex; the curved surface S9 of lens L5 facing the image side is convex, and the curved surface S10 facing the object side is concave; the curved surface S11 of lens L6 facing the image side is convex, and the curved surface S12 facing the object side is convex; the curved surface S13 of lens L7 facing the image side is concave. The object-side surface S14 is convex; the image-side surface S15 of lens L8 is convex, and the object-side surface S16 is convex; the image-side surface S17 of lens L9 is concave, and the object-side surface S18 is convex; the image-side surface S19 of lens L10 is convex, and the object-side surface S20 is convex; the image-side surface S21 of lens L11 is convex, and the object-side surface S22 is convex.

[0045] The third lens group G3, from image side to object side along the same optical axis, includes: lens L12 with positive optical power, lens L13 with positive optical power, lens L14 with positive optical power, and lens L15 with positive optical power. The combined focal length of lenses L12 to L14 is fh = 62.7 mm, satisfying 10 ≤ | | ≤ 13, the focal length of lens L15 is f15 = 60.7mm, satisfying 10 ≤ | | ≤13. Starting from the image side to the object side in the third lens group G3, the design of each surface is as follows: the curved surface S23 of lens L12 facing the image side is convex, and the curved surface S24 facing the object side is concave; the curved surface S25 of lens L13 facing the image side is convex, and the curved surface S26 facing the object side is concave; the curved surface S27 of lens L14 facing the image side is convex, and the curved surface S28 facing the object side is concave; the curved surface S29 of lens L15 facing the image side is convex, and the curved surface S30 facing the object side is concave.

[0046] The surface curvature radius and thickness of each lens, as well as the distance between lenses, are shown in Table 1. Table 1 shows that the working distance, including the glass window C1, is 7.575 mm.

[0047] Table 1 Wavelength: 266nm Referring to the specific parameters and structures of each lens in Table 1 above, the preferred material is Corning HPFS7980ArF grade fused silica glass. This allows the deep ultraviolet microscope objective to achieve a magnification of 40x and an object-side field of view of 0.4mm. These parameters are higher than the field of view of conventional commercial 40x microscope objectives, and it can be used with a 200mm focal length tube lens. The working distance is 7.575mm, significantly larger than that of conventional deep ultraviolet microscope objectives, with a corresponding numerical aperture of 0.85. This improves the object-side field of view and working distance of the deep ultraviolet microscope objective, thereby enhancing the overall performance of the microscope. Furthermore, designed for a center wavelength of 266nm, the designed resolution within this wavelength range matches the theoretical value (diffraction limit).

[0048] Specifically, according to the Rayleigh resolution formula CD=K1× Where λ is used in the calculation formula with a working wavelength of 266nm, the process factor k1 can be calculated to be 0.5. The NA value of the objective lens of this utility model is 0.85. Therefore, the characteristic resolution CD of the deep ultraviolet objective optical system is 157nm. This is based on the formula for calculating NA and collection angle. The characteristic scattered light collection half-angle of the deep ultraviolet objective optical system is 58.2°.

[0049] Optical theoretical simulations were performed on the microscope objectives in the above embodiments. Figure 2 The image shows the MTF (Medium Transfer Function) plot of the microscope objective lens in a specific embodiment when the window is 4 mm. The horizontal axis of the MTF plot represents the resolution, with the unit being line pairs per millimeter (1p / mm), and the vertical axis represents the modulation transfer function (MTF), which is a quantitative description of the lens resolution.

[0050] The MTF value ranges between 0 and 1; the closer it is to 1, the better the lens performance. Figure 2 The MTF curves show that the representative MTF values ​​at 0, 0.5 and maximum fields of view are very close to the diffraction limit, indicating that the optical system designed in this study is close to the diffraction limit of ideal optics and belongs to a very high-quality optical imaging lens.

[0051] in addition, Figure 3The distribution of RMS wave aberrations of the imaging optical system within the field of view of this objective lens is shown. The maximum value of RMS wave aberration within the field of view is 0.0056λ (i.e., RMS wave aberration is 1.5nm), which reflects that the imaging quality of the imaging objective lens of this invention is close to perfect imaging.

[0052] Figure 4 This is a field curvature and distortion diagram of the imaging objective lens in this embodiment, wherein the maximum value of the relative distortion is 0.1029%, corresponding to a field curvature of 15nm.

[0053] The imaging point diagram of the deep ultraviolet objective optical system provided in this application embodiment is as follows: Figure 5 As shown. The horizontal axis represents the image plane size, and the vertical axis represents the zoom bar. The image spot shape is relatively round across the entire field of view, with no obvious coma or astigmatism, exhibiting good image quality.

[0054] In this embodiment, the telecentricity ensures that the object-side full field of view achieves relatively consistent resolution when used as an imaging objective, and ensures the uniformity of coaxial illumination when used as an illumination objective.

[0055] In a preferred embodiment, the edge of the curved surface S19 of the lens L10 or the outer frame serves as an aperture stop, which limits the aperture through which the light beam passes.

[0056] In one alternative embodiment, for quartz glass observation windows of different thicknesses and different wavelengths, this invention can correct various aberrations by optimizing the spherical radius of curvature of the lenses and the distance between the lenses while keeping the numerical aperture and basic structure of the lens group unchanged.

[0057] This embodiment also provides a concept for a microscope imaging scheme, which includes the deep ultraviolet microscope objective lens described in the above embodiment. In a specific embodiment, the deep ultraviolet microscope objective lens can be combined with a 200mm tube lens to achieve an imaging system with a magnification of 40x, an object-side field of view of 0.4mm, and an image-side imaging field of view of 16mm.

[0058] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments, and equivalent variations made in accordance with the claims of this application, still fall within the scope of this application.

Claims

1. A deep ultraviolet microscope objective, characterized in that, It includes a first lens group G1, a second lens group G2, a third lens group G3 and an optical observation window mirror C1 arranged sequentially along the direction from the image side to the object side; The first lens group G1 is a weak negative optical power, consisting of one or more negative meniscus lenses, with an equivalent focal length range of -10mm to -30mm; The second lens group G2 is a weak positive power lens, consisting of one or more alternating positive and negative lenses, with an equivalent focal length range of 50mm to 100mm. The third lens group G3 is a strong positive optical power, consisting of one or more meniscus lenses, with an equivalent focal length range of 10mm to 25mm. The optical observation window mirror C1 has two parallel surfaces that are perpendicular to the optical axis.

2. The deep ultraviolet microscope objective according to claim 1, characterized in that, The first lens group G1 contains three negative meniscus lenses, labeled L1 to L3 from the image side to the object side. Lens L1 has a concave surface S1 facing the image side and a concave surface S2 facing the object side; lens L2 has a concave surface S3 facing the image side and a concave surface S4 facing the object side; lens L3 has a concave surface S5 facing the image side and a concave surface S6 facing the object side.

3. The deep ultraviolet microscope objective according to claim 2, characterized in that, The radius of curvature of surface S1 of lens L1 is -261mm to -262mm, and the radius of curvature of surface S2 is 27mm to 28mm; the radius of curvature of surface S3 of lens L2 is -61mm to -62mm, and the radius of curvature of surface S4 is 55mm to 56mm; the radius of curvature of surface S5 of lens L3 is -173mm to -174mm, and the radius of curvature of surface S6 is 37mm to 38mm.

4. The deep ultraviolet microscope objective according to claim 1, characterized in that, The second lens group G2 contains eight alternating positive and negative lenses, labeled L12 to L15 from image side to object side. Lens L4 has a concave surface S7 facing the image side and a convex surface S8 facing the object side; lens L5 has a convex surface S9 facing the image side and a concave surface S10 facing the object side; lens L6 has a convex surface S11 facing the image side and a convex surface S12 facing the object side; lens L7 has a convex surface S13 facing the image side. The surface S14 facing the object is concave, and the surface S15 facing the image is convex, and the surface S16 facing the object is convex; the surface S17 facing the image is concave, and the surface S18 facing the object is convex; the surface S19 facing the image is convex, and the surface S20 facing the object is convex; the surface S21 facing the image is convex, and the surface S22 facing the object is convex.

5. The deep ultraviolet microscope objective according to claim 4, characterized in that, The radius of curvature of surface S7 of lens L4 is -239mm to -240mm, and the radius of curvature of surface S8 is -50mm to -51mm; the radius of curvature of surface S9 of lens L5 is 68mm to 69mm, and the radius of curvature of surface S10 is 35mm to 36mm; the radius of curvature of surface S11 of lens L6 is 122mm to 123mm, and the radius of curvature of surface S12 is -73mm to -74mm; the radius of curvature of surface S13 of lens L7 is -37mm to -38mm, and the radius of curvature of surface S14 is -77mm to -78mm; the radius of curvature of surface S7 of lens L8 is -239mm to -240mm, and the radius of curvature of surface S8 is -50mm to -51mm; the radius of curvature of surface S9 of lens L5 is 68mm to 69mm, and the radius of curvature of surface S10 is 35mm to 36mm; the radius of curvature of surface S11 of lens L6 is 122mm to 123mm, and the radius of curvature of surface S12 is -73mm to -74mm; the radius of curvature of surface S13 of lens L7 is -37mm to -38mm, and the radius of curvature of surface S14 is -77mm to -78mm; the radius of curvature of surface S14 of lens L7 is -239mm to -240mm, and the radius of curvature of surface S8 is -50mm to -51mm; the radius of curvature of surface S7 of lens L4 is -239mm to -240mm, and the radius of curvature of surface S8 is -50mm to -51mm; the radius of curvature of surface S7 of lens L5 is -23 The radius of curvature of surface S15 is 153mm to 154mm, and the radius of curvature of surface S16 is -108mm to -109mm; the radius of curvature of surface S17 of lens L9 is -31mm to -32mm, and the radius of curvature of surface S18 is -41mm to -42mm; the radius of curvature of surface S19 of lens L10 is 1184mm to 1185mm, and the radius of curvature of surface S20 is -74mm to -75mm; the radius of curvature of surface S21 of lens L11 is 567mm to 568mm, and the radius of curvature of surface S22 is -120mm to -121mm.

6. The deep ultraviolet microscope objective according to claim 1, characterized in that, The third lens group G3 contains four meniscus lenses, labeled L12 to L15 from the image side to the object side. Lens L12 has a convex surface S23 facing the image side and a concave surface S24 facing the object side; lens L13 has a convex surface S25 facing the image side and a concave surface S26 facing the object side; lens L14 has a convex surface S27 facing the image side and a concave surface S28 facing the object side; and lens L15 has a convex surface S29 facing the image side and a concave surface S30 facing the object side.

7. The deep ultraviolet microscope objective according to claim 6, characterized in that, The radius of curvature of surface S23 of lens L12 is 89mm to 90mm, and surface S24 is flat; the radius of curvature of surface S25 of lens L13 is 42mm to 43mm, and the radius of curvature of surface S26 is 98mm to 99mm; the radius of curvature of surface S27 of lens L14 is 42mm to 43mm, and the radius of curvature of surface S28 is 62mm to 63mm; the radius of curvature of surface S29 of lens L15 is 19mm to 20mm, and the radius of curvature of surface S30 is 46mm to 47mm.

8. A deep ultraviolet microscope objective according to any one of claims 1 to 7, characterized in that, The negative meniscus lens, the alternating positive and negative lens, and the meniscus lens are all spherical designs.

9. A deep ultraviolet microscope objective according to claim 8, characterized in that, The negative meniscus lens, the alternating positive and negative lens, and the meniscus lens all employ deep ultraviolet spectral band fused silica lenses.

10. A deep ultraviolet microscope objective according to claim 8, characterized in that, The object size NA is ≥0.85, and the working wavelength is 266nm.

Images