Extremely low back reflection low-power microscope objective

Abstract

The invention discloses an extremely-low back reflection low-power microscope objective, which is applied to a visible light wave band of 400nm-700nm and consists of a first lens group with positive refraction focal power, a second lens group with negative refraction focal power and a third lens group with positive refraction focal power which are sequentially arranged along the light path direction of the microscope objective, a seventh lens is arranged on the side, close to the third lens group, of the second lens group. The seventh lens is a biconcave lens, and the clear aperture of the seventh lens is smaller than that of other lenses of the microscope objective. Extremely low back reflection interference of imaging of the microscope objective is achieved through the seventh lens, good machinability is achieved, and the requirements for high imaging quality, large view field and low stray light in the semiconductor field are met.

Description

Technical Field

[0001] This invention relates to the field of microscope objectives, specifically to a low-magnification microscope objective with extremely low back reflection. Background Technology

[0002] In applications such as semiconductor defect detection and micro / nano structure observation, high resolution, large field of view, and low stray light imaging are key factors in ensuring detection accuracy and efficiency. Currently, while high numerical aperture microscope objectives can provide high resolution, their field of view is often limited, making it difficult to meet the needs of large-scale observation. On the other hand, traditional low-magnification objectives, although possessing a large field of view, often suffer from reduced image resolution and contrast due to their small numerical aperture, insufficient aberration correction, and severe back reflection problems, failing to meet the requirements of high-precision semiconductor detection.

[0003] Especially in optical inspection modes such as bright-field, dark-field, and interferometric imaging, stray light and back reflection from microscope objectives significantly reduce the image signal-to-noise ratio, affecting defect identification capabilities. Existing low-magnification objectives often fail to adequately balance aberration correction, transmittance optimization, and reflection suppression in their design, resulting in poor performance when matched with next-generation semiconductor inspection systems. Therefore, a high-performance microscope objective is needed that combines a large numerical aperture, a wide field of view, low stray light, and excellent back reflection suppression capabilities to improve imaging quality and inspection reliability. Summary of the Invention

[0004] Technical objective: To address the shortcomings of existing low-magnification microscope objectives, this invention discloses an extremely low back reflection low-magnification microscope objective.

[0005] Technical solution: To achieve the above technical objectives, the present invention adopts the following technical solution: An ultra-low back-reflection low-magnification microscope objective comprises a first lens group with positive refractive power, a second lens group with negative refractive power, and a third lens group with positive refractive power, arranged sequentially along the optical path of the microscope objective; 0.6≥|fG1 / fobj|≥0.4, 0.3≥|fG2 / fobj|≥0.1, 0.5≥|fG3 / fobj|≥0.3, where fG1, fG2, and fG3 represent the focal lengths of the first, second, and third lens groups, respectively, and fobj represents the focal length of the microscope objective; a seventh lens is provided on the side of the second lens group closest to the third lens group, and the seventh lens is a biconcave lens with a aperture smaller than that of the other lenses of the microscope objective.

[0006] Preferably, the first lens group of the present invention is a cemented doublet lens, which consists of a first lens with positive optical power and a second lens with negative optical power arranged sequentially along the optical path direction.

[0007] Preferably, the first lens of the present invention is a biconvex lens, and the second lens is a plano-concave lens.

[0008] Preferably, the first lens of the present invention has a d-ray refractive index of n1 and an Abbe number of v1, where 1.6 ≥ n1 ≥ 1.5 and 70 ≥ v1 ≥ 60; and the second lens has a d-ray refractive index of n2 and an Abbe number of v2, where 1.6 ≥ n2 ≥ 1.5 and 65 ≥ v2 ≥ 55.

[0009] Preferably, the second lens group of the present invention includes a third lens with negative optical power, a fourth lens with positive optical power, a fifth lens with positive optical power, a sixth lens with positive optical power, and a seventh lens arranged sequentially along the optical path direction, wherein the third lens and the fourth lens form a cemented doublet lens.

[0010] Preferably, the third lens of the present invention is a biconcave lens, the fourth lens is a meniscus lens, the fifth lens is a biconvex lens, and the sixth lens is a plano-convex lens.

[0011] Preferably, the refractive index and Abbe number of the third lens of the present invention are n3 and v3, respectively, with 1.8 ≥ n3 ≥ 1.7 and 55 ≥ v3 ≥ 45; the refractive index and Abbe number of the fourth lens are n4 and v4, respectively, with 1.6 ≥ n4 ≥ 1.5 and 75 ≥ v4 ≥ 65; the refractive index and Abbe number of the fifth lens are n5 and v5, respectively, with 1.55 ≥ n5 ≥ 1.45 and 85 ≥ v5 ≥ 80; the refractive index and Abbe number of the sixth lens are n6 and v6, respectively, with 1.7 ≥ n6 ≥ 1.6 and 35 ≥ v6 ≥ 30; and the refractive index and Abbe number of the seventh lens are n7 and v7, respectively, with 1.6 ≥ n7 ≥ 1.5 and 60 ≥ v7 ≥ 50.

[0012] Preferably, the third lens group of the present invention consists of an eighth lens and a ninth lens arranged sequentially along the optical path direction, and both the eighth lens and the ninth lens are positive power lenses.

[0013] Preferably, the eighth lens of the present invention is a biconvex lens, and the ninth lens is a meniscus lens.

[0014] Preferably, the d-ray refractive index and Abbe number of the eighth lens of the present invention are n8 and v8, respectively, 1.8≥n8≥1.7, 60≥v8≥50; the d-ray refractive index and Abbe number of the ninth lens are n9 and v9, respectively, 1.96≥n9≥1.9, 36≥v9≥33.

[0015] Beneficial effects: The ultra-low back reflection low-magnification microscope objective disclosed in this invention has the following beneficial effects: 1. The microscope objective of the present invention uses a positive-negative-positive lens group structure, and sets a seventh lens at the second lens group with negative refractive power. The seventh lens collects light and expands the beam. By limiting the light transmission aperture of the seventh lens, the incident angle of the light is increased, thereby suppressing the passage of stray light reflected from the lens on the microscope objective and reducing the influence of stray light on imaging.

[0016] 2. The first lens group of the present invention consists of a doublet lens composed of a biconvex lens and a plano-concave lens. The reasonable setting of the refractive index and Abbe number of the two lenses effectively increases the field of view and meets the wide-range observation needs of low-magnification microscope objectives.

[0017] 3. The second lens group of the present invention, through the combination of a doublet consisting of a biconcave lens and a meniscus lens, a biconvex lens, a plano-convex lens, and a biconcave lens, and the reasonable setting of the refractive index and Abbe number of the five lenses, effectively corrects spherical aberration, coma, astigmatism, and chromatic aberration, thereby improving the imaging quality.

[0018] 4. The third lens group of the present invention consists of a biconvex lens and a meniscus lens, which effectively corrects the astigmatism and field curvature inside the microscope objective and controls the distortion within a small range, thus ensuring the consistency of the image plane in different fields of view. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0020] Figure 1 This is a schematic diagram of the optical structure of the microscope objective of the present invention; Figure 2 This is a modulation transfer function curve of the microscope objective of the present invention; Figure 3 This is a chromatic aberration curve of the microscope objective of this invention; Figure 4 This is a field curvature and distortion curve of the microscope objective of the present invention; Figure 5 This is a two-dimensional energy map of the image plane when the object side is set as a reflecting surface after the microscope objective of the present invention is combined with a 200mm focal length ideal tube lens; Figure 6 This is a two-dimensional energy map of the image plane when the object side is set as the absorption surface after the microscope objective of this invention is combined with a 200mm focal length ideal tube lens; Among them, G1-first lens group, G2-second lens group, G3-third lens group, L1-first lens, L2-second lens, L3-third lens, L4-fourth lens, L5-fifth lens, L6-sixth lens, L7-seventh lens, L8-eighth lens, and L9-ninth lens. Detailed Implementation

[0021] Reference will now be made in detail to embodiments of the present disclosure, one or more of which are set forth herein. Each embodiment and example is provided by way of explanation of the apparatus, composition, and materials of the present disclosure, and not by way of limitation. Rather, the following description provides convenient illustrations for implementing exemplary embodiments of the present disclosure. Indeed, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope or spirit of the present disclosure.

[0022] like Figure 1 As shown, an ultra-low back-reflection low-magnification microscope objective comprises a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power, and a third lens group G3 with positive refractive power, arranged sequentially along the optical path of the microscope objective; 0.6≥|fG1 / fobj|≥0.4, 0.3≥|fG2 / fobj|≥0.1, 0.5≥|fG3 / fobj|≥0.3, where fG1, fG2, and fG3 represent the focal lengths of the first lens group G1, the second lens group G2, and the third lens group G3, respectively, and fobj represents the focal length of the microscope objective; a seventh lens L7 is provided on the side of the second lens group G2 closest to the third lens group G3, and the seventh lens L7 is a biconcave lens with a light-transmitting aperture smaller than that of the other lenses of the microscope objective.

[0023] The three lens groups form a positive-negative-positive optical architecture along the optical path. The seventh lens L7 is positioned at the "waist" of the optical path, that is, at the point where the light beam height is the smallest within the entire optical path. The seventh lens L7 collects light and acts as a beam expander. Due to the small aperture of the seventh lens L7, the incident angle of the light beam is increased, thereby reducing the amount of stray light transmitted and minimizing the impact of stray light on imaging. Preferably, the incident angle of the light beam at the maximum field of view and the maximum aperture is maintained at the aperture of the seventh lens L7.

[0024] The first lens group G1 of this invention is a cemented doublet lens, consisting of a first lens L1 with positive optical power and a second lens L2 with negative optical power arranged sequentially along the optical path. The first lens L1 is a biconvex lens, and the second lens L2 is a plano-concave lens. The cemented doublet lens composed of the first lens L1 and the second lens L2 effectively increases the field of view of the microscope objective and expands the observation area.

[0025] In the embodiments of the present invention, the maximum field of view of the microscope objective is 34, the working wavelength is 400-700nm, the d-ray refractive index and Abbe number of the first lens L1 of the present invention are n1 and v1, respectively, 1.6≥n1≥1.5, 70≥v1≥60; the d-ray refractive index and Abbe number of the second lens L2 are n2 and v2, respectively, 1.6≥n2≥1.5, 65≥v2≥55.

[0026] The second lens group G2 of the present invention includes a third lens L3 with negative optical power, a fourth lens L4 with positive optical power, a fifth lens L5 with positive optical power, a sixth lens L6 with positive optical power, and a seventh lens L7 arranged sequentially along the optical path direction. The third lens L3 and the fourth lens L4 form a cemented doublet lens. The lens combination corrects spherical aberration, coma, astigmatism, and chromatic aberration, thereby improving the imaging quality of the microscope objective.

[0027] Specifically, the third lens L3 of this invention is a biconcave lens, the fourth lens L4 is a meniscus lens, the fifth lens L5 is a biconvex lens, and the sixth lens L6 is a plano-convex lens; the d-ray refractive index and Abbe number of the third lens L3 are n3 and v3, respectively, 1.8≥n3≥1.7, 55≥v3≥45; the d-ray refractive index and Abbe number of the fourth lens L4 are n4 and v4, respectively, 1.6≥n4≥1.5, 75≥v4≥65; the d-ray refractive index and Abbe number of the fifth lens L5 are n5 and v5, respectively, 1.55≥n5≥1.45, 85≥v5≥80; the d-ray refractive index and Abbe number of the sixth lens L6 are n6 and v6, respectively, 1.7≥n6≥1.6, 35≥v6≥30; the d-ray refractive index and Abbe number of the seventh lens L7 are n7 and v7, respectively, 1.6≥n7≥1.5, 60≥v7≥50.

[0028] The third lens group G3 of the present invention consists of an eighth lens L8 and a ninth lens L9 arranged sequentially along the optical path. Both the eighth lens L8 and the ninth lens L9 are positive power lenses. The third lens group G3 corrects the astigmatism and field curvature inside the microscope objective, controls the distortion within a small range, and ensures the consistency of the image plane in different fields of view.

[0029] Specifically, the eighth lens L8 of this invention is a biconvex lens, and the ninth lens L9 is a meniscus lens. The d-ray refractive index and Abbe number of the eighth lens L8 are n8 and v8, respectively, where 1.8 ≥ n8 ≥ 1.7 and 60 ≥ v8 ≥ 50; the d-ray refractive index and Abbe number of the ninth lens L9 are n9 and v9, respectively, where 1.96 ≥ n9 ≥ 1.9 and 36 ≥ v9 ≥ 33.

[0030] By combining the first lens group G1, the second lens group G2, and the third lens group G3, the microscope objective of the present invention possesses the characteristics of high imaging quality, large field of view, and low stray light. The lens parameters provided in the embodiments of the present invention are shown in Table 1.

[0031] Table 1. Parameters of Microscope Objective Lenses

[0032] The surface numbers are marked according to the direction of the light path for different lens surfaces. Cemented doublet lenses share the same surface number. OBJ is the object plane and IMA is the image plane.

[0033] S1 represents the glass surface of the first lens L1 closest to the actual image side, S2 represents the glass surface where the first lens L1 and the second lens L2 are bonded together, and S3 represents the glass surface of the second lens L2 away from the actual image side. In Table 1, the radii of curvature of S1 and S2 correspond to the radii of curvature of the two glass surfaces of the first lens L1, and the radii of curvature of S2 and S3 correspond to the radii of curvature of the two glass surfaces of the second lens L2, respectively. The thickness corresponding to S1 is the thickness of the first lens L1, and the material parameters corresponding to S1 are the glass parameters of the first lens L1. In Table 1, the thickness corresponding to S2 is the thickness of the second lens L2, and the material parameters are the glass parameters of the second lens L2.

[0034] The thickness of S3 represents the distance between the second lens L2 and the third lens L3.

[0035] S4 represents the glass surface of the third lens L3 closest to the second lens L2, S5 represents the glass surface where the third lens L3 and the fourth lens L4 are bonded together, and S6 represents the glass surface of the fourth lens L4 away from the third lens L3. In Table 1, the radii of curvature of S4 and S5 correspond to the radii of curvature of the two glass surfaces of the third lens L3, and the radii of curvature of S5 and S6 correspond to the radii of curvature of the two glass surfaces of the fourth lens L4. In Table 1, the thickness corresponding to S4 is the thickness of the third lens L3, and the material parameters are the glass parameters of the third lens L3. In Table 1, the thickness corresponding to S5 is the thickness of the fourth lens L4, and the material parameters are the glass parameters of the fourth lens L4.

[0036] The thickness of S6 represents the distance between the fourth lens L4 and the fifth lens L5.

[0037] S7 represents the glass surface of the fifth lens L5 on the side closer to the fourth lens L4, and S8 represents the glass surface of the fifth lens L5 on the side away from the fourth lens L4. In Table 1, the radii of curvature of S7 and S8 correspond to the radii of curvature of the two glass surfaces of the fifth lens L5, respectively. The thickness corresponding to S7 is the thickness of the fifth lens, and the material parameters are the glass parameters of the fifth lens L5.

[0038] The thickness of S8 represents the distance between the fifth lens L5 and the sixth lens L6.

[0039] S9 represents the glass surface of the sixth lens L6 on the side closer to the fifth lens L5, and S10 represents the glass surface of the sixth lens L6 on the side away from the fifth lens L5. In Table 1, the radii of curvature of S9 and S10 correspond to the radii of curvature of the two glass surfaces of the sixth lens L6, respectively. The thickness corresponding to S9 is the thickness of the sixth lens L6, and the material parameters are the glass parameters of the sixth lens L6.

[0040] The thickness of S10 represents the distance between the sixth lens L6 and the seventh lens L7.

[0041] S11 represents the glass surface of the seventh lens L7 on the side closer to the sixth lens L6, and S12 represents the glass surface of the seventh lens L7 on the side away from the sixth lens L6. In Table 1, the radii of curvature of S11 and S12 correspond to the radii of curvature of the two glass surfaces of the seventh lens L7, respectively. The thickness corresponding to S11 is the thickness of the seventh lens L7, and the material parameters are the glass parameters of the seventh lens L7.

[0042] The thickness of S12 represents the distance between the seventh lens L7 and the eighth lens L8.

[0043] S13 represents the glass surface of the eighth lens L8 on the side close to the seventh lens L7, and S14 represents the glass surface of the eighth lens L8 on the side away from the seventh lens L7. In Table 1, the radii of curvature of S13 and S14 correspond to the radii of curvature of the two glass surfaces of the eighth lens L8, respectively. The thickness corresponding to S13 is the thickness of the eighth lens L8, and the material parameters are the glass parameters of the eighth lens L8.

[0044] The thickness of S14 represents the distance between the eighth lens L8 and the ninth lens L9.

[0045] S15 represents the glass surface of the ninth lens L9 on the side close to the eighth lens L8, and S16 represents the glass surface of the ninth lens L9 on the side away from the eighth lens L8. In Table 1, the radii of curvature of S15 and S16 correspond to the radii of curvature of the two glass surfaces of the ninth lens L9, the thickness corresponding to S15 is the thickness of the ninth lens L9, and the material parameters are the glass parameters of the ninth lens L9. The thickness of S16 represents the distance between the ninth lens L9 and the object surface.

[0046] like Figure 2 As shown, Figure 2 The horizontal axis represents the spatial frequency (lp / mm), and the vertical axis represents the magnitude of the optical modulation function. From the figure, it can be seen that the MTF curves of each field of view of the microscope objective basically coincide with the diffraction limit curve, which proves that the microscope objective in this embodiment has excellent imaging performance.

[0047] like Figure 3The figure shows the transverse chromatic aberration curve of the microscope objective in this embodiment, where the horizontal axis represents the offset (μm) and the vertical axis represents the field of view. The figure shows that the lateral image plane offset of the microscope objective in this example for different wavelengths of light in different fields of view is less than 0.3 μm, indicating that the microscope objective in this example has corrected for transverse chromatic aberration.

[0048] like Figure 4 The diagram shows the field curvature and distortion curves of the microscope objective in this embodiment. The vertical axis represents the field of view. The left side is the field curvature diagram, and the horizontal axis is the field curvature. The field curvature is less than 0.03 mm. The right side is the distortion curve diagram, and the horizontal axis is the distortion percentage. The distortion is less than 0.2%. This indicates that the microscope objective in this example has corrected the field curvature and distortion, which can achieve better image quality requirements.

[0049] like Figure 5 and Figure 6 The diagram shows the two-dimensional energy distribution of the microscope objective in this embodiment when combined with a 200mm focal length ideal tube lens, with the object side set as either a reflecting or absorbing surface, reaching the image plane. The vertical axis represents the Y-axis dimension on the image plane, and the horizontal axis represents the X-axis dimension. A comparison of the two diagrams reveals extremely low back reflection, meeting the low stray light requirements of the semiconductor field.

[0050] The microscope objective provided in this embodiment meets the following optical specifications: focal length of 100mm, object-side field of view of 17mm, NA of 0.11, working distance of more than 17mm, optical distortion of less than 0.3%, transverse chromatic aberration of less than 1μm, and telecentricity of less than 0.5°, which meets the requirements for the use of low-magnification microscope objectives and reduces the impact of lens back reflection on imaging.

[0051] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-reflection, low-magnification microscope objective, characterized in that, It consists of a first lens group (G1) with positive refractive power, a second lens group (G2) with negative refractive power, and a third lens group (G3) with positive refractive power arranged sequentially along the optical path of the microscope objective. 0.6≥|fG1 / fobj|≥0.4, 0.3≥|fG2 / fobj|≥0.1, 0.5≥|fG3 / fobj|≥0.3, where fG1, fG2, and fG3 represent the focal lengths of the first lens group (G1), the second lens group (G2), and the third lens group (G3), respectively, and fobj represents the focal length of the microscope objective; the second lens group (G2) has a seventh lens (L7) on the side closer to the third lens group (G3), and the seventh lens (L7) is a biconcave lens with a light-transmitting aperture smaller than that of the other lenses of the microscope objective.

2. The low-reflection, low-magnification microscope objective according to claim 1, characterized in that, The first lens group (G1) is a cemented doublet lens, consisting of a first lens (L1) with positive optical power and a second lens (L2) with negative optical power arranged sequentially along the optical path.

3. The low-back-reflection low-magnification microscope objective according to claim 2, characterized in that, The first lens (L1) is a biconvex lens, and the second lens (L2) is a plano-concave lens.

4. The low-back-reflection low-magnification microscope objective according to claim 2, characterized in that, The d-ray refractive index and Abbe number of the first lens (L1) are n1 and v1, respectively, with 1.6≥n1≥1.5 and 70≥v1≥60; the d-ray refractive index and Abbe number of the second lens (L2) are n2 and v2, respectively, with 1.6≥n2≥1.5 and 65≥v2≥55.

5. The low-back-reflection low-magnification microscope objective according to claim 1, characterized in that, The second lens group (G2) consists of a third lens (L3) with negative optical power, a fourth lens (L4) with positive optical power, a fifth lens (L5) with positive optical power, a sixth lens (L6) with positive optical power, and a seventh lens (L7) arranged sequentially along the optical path direction, wherein the third lens (L3) and the fourth lens (L4) form a cemented doublet lens.

6. The low-back-reflection low-magnification microscope objective according to claim 5, characterized in that, The third lens (L3) is a biconcave lens, the fourth lens (L4) is a meniscus lens, the fifth lens (L5) is a biconvex lens, and the sixth lens (L6) is a plano-convex lens.

7. The low-reflection, low-magnification microscope objective according to claim 5, characterized in that, The refractive index and Abbe number of the third lens (L3) are n3 and v3, respectively, with 1.8 ≥ n3 ≥ 1.7 and 55 ≥ v3 ≥ 45; the refractive index and Abbe number of the fourth lens (L4) are n4 and v4, respectively, with 1.6 ≥ n4 ≥ 1.5 and 75 ≥ v4 ≥ 65; the refractive index and Abbe number of the fifth lens (L5) are n5 and v5, respectively, with 1.55 ≥ n5 ≥ 1.45 and 85 ≥ v5 ≥ 80; the refractive index and Abbe number of the sixth lens (L6) are n6 and v6, respectively, with 1.7 ≥ n6 ≥ 1.6 and 35 ≥ v6 ≥ 30; the refractive index and Abbe number of the seventh lens (L7) are n7 and v7, respectively, with 1.6 ≥ n7 ≥ 1.5 and 60 ≥ v7 ≥ 50.

8. The low-reflection, low-magnification microscope objective according to claim 1, characterized in that, The third lens group (G3) consists of an eighth lens (L8) and a ninth lens (L9) arranged sequentially along the optical path direction. Both the eighth lens (L8) and the ninth lens (L9) are positive power lenses.

9. A low-back-reflection, low-magnification microscope objective according to claim 8, characterized in that, The eighth lens (L8) is a biconvex lens, and the ninth lens (L9) is a meniscus lens.

10. A low-back-reflection, low-magnification microscope objective according to claim 8, characterized in that, The d-ray refractive index and Abbe number of the eighth lens (L8) are n8 and v8, respectively, with 1.8≥n8≥1.7 and 60≥v8≥50; the d-ray refractive index and Abbe number of the ninth lens (L9) are n9 and v9, respectively, with 1.96≥n9≥1.9 and 36≥v9≥33.

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