Large field of view imaging objective

Abstract

This invention provides a large field-of-view imaging objective, employing a dual telecentric optical structure composed of lens groups with positive, positive, negative, and positive optical powers sequentially along the beam incident direction. The total objective length is ≤1100mm, suitable for a broad spectrum of 450-650nm, with a magnification of -20x, an object-side numerical aperture (NA) ≤0.45, and an object-side field-of-view diameter of 4.1mm. The imaging objective provided by this invention features a large aperture and a wide field of view, improving objective resolution and increasing yield. Furthermore, the imaging objective has a large numerical aperture angle and a small depth-of-field range, making it suitable for detecting different patterns on wafer surfaces. It provides sharper imaging of pit edges, meeting the wafer defect detection requirements of new processes.

Description

Technical Field

[0001] This invention relates to the field of imaging technology, and more particularly to a large field-of-view imaging objective. Background Technology

[0002] With the development of industrial technology, the requirements for detection accuracy, detection speed and detection size are constantly increasing in the fields of biological, genetic, medical and industrial testing. Therefore, the requirements for automated optical inspection (AOI) equipment and imaging lenses are also getting higher and higher. In particular, imaging lenses that can meet the needs of large workpieces, large field of view and distortion-free precision inspection are very difficult to design and manufacture. Summary of the Invention

[0003] The purpose of this invention is to provide a large field-of-view imaging objective lens to achieve aberration correction of a large aperture, large field of view, and dual telecentric system, thereby improving the resolution of the objective lens and increasing productivity.

[0004] To achieve the above objectives, the present invention provides a large field-of-view imaging objective, comprising: a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 arranged sequentially along the incident direction of the light beam, wherein the first lens group G1 is used to converge a large-angle light beam; the second lens group G2 is used to correct the aberrations of the imaging objective; the third lens group G3 is used to magnify the real image formed by the first lens group G1 and the second lens group G2 into a virtual image to achieve high magnification, and is also used to correct field curvature; the fourth lens group G4 is used to realize the formation of a real image from the virtual image generated by the third lens group G3.

[0005] Optionally, the first lens group G1, the second lens group G2, and the fourth lens group G4 have positive optical power, and the third lens group G3 has negative optical power.

[0006] Optionally, the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship:

[0007] 0.1 < |f1 / f2| < 0.5

[0008] 3<|f2 / f3|<8

[0009] 0.1 < |f3 / f4| < 0.5

[0010] 0.1 < |f1 / f4| < 1

[0011] Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

[0012] Optionally, the first lens group G1 consists of at least two lenses, including two positive lenses;

[0013] The second lens group G2 consists of at least 7 lenses, including at least two cemented doublet lenses or one cemented triplet lens group;

[0014] The third lens group G3 consists of at least two lenses, including two negative lenses;

[0015] The fourth lens group G4 consists of at least two lenses, including two positive lenses;

[0016] Except for the two cemented doublet lens groups and the three cemented triplet lens group, the remaining lenses are all spherical single lenses.

[0017] Optionally, the first lens group G1 consists of two lenses, which are positive lens L1 and positive lens L2 in sequence along the incident direction of the light beam;

[0018] The second lens group G2 consists of 9 lenses, which are arranged in sequence along the incident direction of the light beam as follows: positive lens L3, lens L4 and lens L5 forming a cemented doublet lens group G2-1 with negative optical power; positive lens L6, negative lens L7, lens L8 and lens L9 forming a cemented doublet lens group G2-2 with negative optical power; and lens L10 and lens L11 forming a cemented doublet lens group G2-3 with positive optical power.

[0019] The third lens group G3 consists of 3 lenses, which are arranged sequentially along the incident direction of the light beam as a doublet lens group G3-1 with positive optical power, composed of lens L12 and lens L13, and a negative lens L14.

[0020] The fourth lens group G4 consists of three lenses, which are, in order, a negative lens L15, a positive lens L16, and a positive lens L17 along the incident direction of the light beam.

[0021] Optionally, lens L4 and lens L8 are negative lenses, lens L5, lens L9 and lens L10 are positive lenses, lens L11 is either a positive or negative lens, lens L12 is either a positive or negative lens, and lens L13 is a positive lens.

[0022] Optionally, at least two positive lenses in the first lens group G1 are made of flint glass.

[0023] In the second lens group G2, the negative lenses in the cemented doublet are all made of flint glass, and the positive lenses in the cemented doublet are all made of crown glass, or both lenses in the cemented doublet are made of crown glass.

[0024] At least one positive lens in the third lens group G3 is made of crown glass.

[0025] At least one negative lens in the fourth lens group G4 is made of flint glass.

[0026] Optionally, the first lens group G1 consists of two lenses, which are positive lens L1 and positive lens L2 in sequence along the incident direction of the light beam;

[0027] The second lens group G2 consists of 11 lenses, which are arranged in the following order along the incident direction of the light beam: G2-1, a cemented triplet lens group with negative optical power composed of positive lens L3, lens L4, lens L5 and lens L6; G2-2, a cemented doublet lens group with positive optical power composed of lens L7 and lens L8; G2-3, a cemented doublet lens group with positive optical power composed of negative lens L9, negative lens L10 and positive lens L11; and G2-4, a cemented doublet lens group with positive optical power composed of lens L12 and lens L13.

[0028] The third lens group consists of four lenses, which are, in sequence along the incident direction of the light beam, a doublet lens group G3-1 with negative optical power composed of lens L14 and lens L15, negative lens L16 and negative lens L17.

[0029] The fourth lens group consists of three lenses, which are, in order, a negative lens L18, a positive lens L19, and a positive lens L20 along the incident direction of the light beam.

[0030] Optionally, lens L4, lens L6 and lens L14 are negative lenses, lens L5, lens L7, lens L11, lens L12 and lens L15 are positive lenses, lens L8 is a positive or negative lens, lens L10 is a positive or negative lens, and lens L13 is a positive or negative lens.

[0031] Optionally, at least two positive lenses in the first lens group G1 are made of flint glass.

[0032] In the second lens group G2, the negative lenses in the cemented doublet lens group are all made of flint glass, the positive lenses in the cemented doublet lens group are all made of crown glass, or both lenses in the cemented doublet lens group are made of crown glass, and at least one negative lens in the triplet lens group is made of flint glass.

[0033] At least one negative lens in the third lens group G3 is made of flint glass.

[0034] At least one negative lens in the fourth lens group G4 is made of flint glass.

[0035] Optionally, an illumination beam splitter and an aperture are sequentially arranged between the first lens group G1 and the second lens group G2.

[0036] Optionally, the object-side working distance of the large field-of-view imaging objective is >45mm, and the distortion is less than 0.5%.

[0037] Optionally, the total length of the large field-of-view imaging objective lens is less than 1100 mm, the object-side numerical aperture (NA) is less than or equal to 0.45, and the magnification is -20x.

[0038] Optionally, the diameter of the object's field of view is 4.1 mm.

[0039] Optionally, the wide field-of-view imaging objective is suitable for a spectrum of 450-650 nm.

[0040] In summary, the large field-of-view imaging objective provided by this invention employs a dual telecentric optical structure composed of lens groups with positive, positive, negative, and positive optical powers sequentially along the beam incident direction. The total objective length is ≤1100mm, suitable for a wide spectrum of 450-650nm, with a magnification of -20x, an object-side numerical aperture (NA) ≤0.45, and an object-side field-of-view diameter of 4.1mm. The imaging objective provided by this invention features a large aperture and a large field of view, improving the objective's resolution and increasing yield. Furthermore, the imaging objective has a large numerical aperture angle and a small depth-of-field range, making it suitable for detecting different patterns on wafer surfaces. It provides sharper imaging of pit edges, meeting the requirements for wafer defect detection under new processes. Attached Figure Description

[0041] Figure 1 An optical structure diagram of a large field-of-view imaging objective lens provided in an embodiment of the present invention;

[0042] Figure 2 The transfer function (MTF) diagram of an imaging objective optical system provided in an embodiment of the present invention;

[0043] Figure 3 This is an image of astigmatism and distortion of an imaging objective lens according to an embodiment of the present invention;

[0044] Figure 4 An optical structure diagram of a large field-of-view imaging objective lens provided in another embodiment of the present invention;

[0045] Figure 5 A transfer function (MTF) diagram of an imaging objective optical system provided in another embodiment of the present invention;

[0046] Figure 6 This is an image of astigmatism and distortion of an imaging objective lens according to another embodiment of the present invention. Detailed Implementation

[0047] The large field-of-view imaging objective of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description and drawings; however, it should be noted that the concept of the technical solution of the present invention can be implemented in many different forms and is not limited to the specific embodiments described herein. The accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0048] The terms “first,” “second,” etc., used in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a particular order or chronological sequence. It should be understood that these terms, used so in this way, may be replaced where appropriate, for example, to allow embodiments of the invention described herein to operate in a different order than that described or shown herein. Similarly, if the methods described herein comprise a series of steps, and the order of these steps presented herein is not necessarily the only possible order in which these steps can be performed, and some described steps may be omitted and / or some other steps not described herein may be added to the method. If a component in one figure is identical to a component in another figure, although these components are readily identifiable in all figures, this specification will not label all identical components in every figure for the sake of clarity.

[0049] This invention provides a large field-of-view imaging objective lens, comprising: a first lens group G1 with positive optical power, an illumination beam splitter R, an aperture stop, a second lens group G2 with positive optical power, a third lens group G3 with negative optical power, and a fourth lens group G4 with positive optical power, arranged sequentially along the incident direction of the light beam. The first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship:

[0050] 0.1 < |f1 / f2| < 0.5

[0051] 3<|f2 / f3|<8

[0052] 0.1 < |f3 / f4| < 0.5

[0053] 0.1 < |f1 / f4| < 1

[0054] Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

[0055] In this invention, the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a dual telecentric optical path on the object and image sides. The aperture stop of the imaging objective lens is located between the first lens group G1 and the second lens group G2, and the illumination beam splitter R is located between the first lens group G1 and the aperture stop. The effective aperture of the objective lens can be adjusted by adjusting the size of the aperture stop, i.e., the numerical aperture of the objective lens can be adjusted by adjusting the aperture stop to adapt to different coherent or incoherent illumination application scenarios. Specifically, the principal rays of each field of view on the object side are incident on the front surface of the first lens approximately parallel to the optical axis. On the object side, the principal rays of each field of view on the object surface are incident on the first optical element parallel to the optical axis, with the angle between the principal rays and the optical axis being less than 5 mrad. On the image side, the principal rays of each field of view point are emitted approximately parallel to the optical axis and imaged on the image plane, with the angle between the principal rays and the optical axis being less than 2 mrad.

[0056] The imaging objective provided by this invention is a wide field of view, large aperture, high resolution, and wide visible light spectrum imaging objective. The total length of the objective does not exceed 1100mm, it is suitable for a wide spectrum of 450-650nm, the magnification is -20x, the numerical aperture (NA) of the object side is less than or equal to 0.45, and the object side field of view is 4.1mm in diameter.

[0057] The first lens group G1 is located in front of the illumination beam splitter R and is used to converge a large-angle beam into the illumination beam splitter R at a smaller incident angle. The first lens group G1 consists of at least two lenses, including two positive lenses.

[0058] The second lens group G2 is located behind the aperture stop and is used to correct aberrations of the optical system, including spherical aberration, coma, and chromatic aberration. The second lens group G2 consists of at least 7 lenses, including at least two cemented doublet lenses or one cemented triplet lens group.

[0059] The third lens group G3 has a long air gap with the second lens group G2, which is used to magnify the real image formed by the front lens group into a virtual image to achieve high magnification, and at the same time to correct field curvature. The third lens group G3 is composed of at least two lenses, including two negative lenses.

[0060] The fourth lens group G4 is located in front of the imaging plane, enabling the virtual image generated by the third lens group G3 to be transformed into a real image. The fourth lens group G4 consists of at least two lenses, including two positive lenses.

[0061] Except for the cemented doublet lens group and the cemented triplet lens group, all other lenses are spherical single lenses.

[0062] Optical materials are generally classified into two categories according to their refractive index and Abbe number: Category A: flint glass materials, which are high refractive index materials with low Abbe numbers, i.e., a refractive index greater than 1.52 and an Abbe number less than 60; Category B: crown glass materials, which are low refractive index materials with high Abbe numbers, i.e., a refractive index less than 1.52 and an Abbe number greater than 60. Specifically, in this invention, at least one positive lens in the first lens group G1 is made of flint glass; in the second lens group G2, all negative lenses in the cemented doublet are made of flint glass, and all positive lenses in the cemented doublet are made of crown glass, or both lenses in the cemented doublet are made of crown glass, and at least one negative lens in the cemented triplet is made of flint glass; at least one negative lens in the third lens group G3 is made of flint glass; and at least one negative lens in the fourth lens group G4 is made of flint glass.

[0063] Example 1

[0064] Figure 1 This is an optical structure diagram of the large field-of-view imaging objective provided in this embodiment, with reference to... Figure 1 As shown, the large field-of-view imaging objective provided by the present invention includes: a first lens group G1 with positive optical power, an illumination beam splitter, an aperture stop, a second lens group G2 with positive optical power, a third lens group G3 with negative optical power, and a fourth lens group G4 with positive optical power, arranged sequentially along the incident direction of the light beam (from the object plane OBJ to the image plane IMA), wherein the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship:

[0065] 0.1 < |f1 / f2| < 0.5

[0066] 3<|f2 / f3|<8

[0067] 0.1 < |f3 / f4| < 0.5

[0068] 0.1 < |f1 / f4| < 1

[0069] Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

[0070] Specifically, the first lens group G1 consists of two lenses, namely positive lens L1 and positive lens L2, which are arranged sequentially along the incident direction of the light beam. The positive lens L1 is a meniscus positive lens, and the positive lens L2 is a biconvex positive lens.

[0071] The second lens group G2 consists of 9 lenses, arranged sequentially along the incident direction of the light beam as follows: a cemented doublet group G2-1 with negative optical power consisting of positive lens L3, lens L4 and lens L5; a cemented doublet group G2-2 with negative optical power consisting of positive lens L6, negative lens L7, lens L8 and lens L9; and a cemented doublet group G2-3 with positive optical power consisting of lens L10 and lens L11. Among them, lens L4 and lens L8 are negative lenses, lens L5, lens L9 and lens L10 are positive lenses, and lens L11 is either a positive lens or a negative lens. For example, the positive lens L3 is a plano-convex positive lens, the lens L4 is a biconcave negative lens, the lens L5 is a meniscus positive lens, the positive lens L6 is a biconvex positive lens, the negative lens L7 is a plano-concave negative lens, the lens L8 is a plano-concave negative lens, the lens L9 is a biconvex positive lens, the lens L10 is a biconvex positive lens, and the lens L11 is a plano-concave negative lens or a biconcave negative lens.

[0072] The third lens group G3 consists of three lenses, arranged sequentially along the incident direction of the light beam: a cemented doublet lens group G3-1 with positive optical power composed of lens L12 and lens L13, and a negative lens L14. Lens L12 is either a positive or negative lens, and lens L13 is a positive lens. For example, lens L12 is a plano-concave negative lens, the positive lens L3 is a meniscus positive lens or a biconvex positive lens, and the negative lens L14 is a biconcave negative lens.

[0073] The fourth lens group G4 consists of two lenses, namely a negative lens L15, a positive lens L16, and a positive lens L17, arranged sequentially along the incident direction of the light beam. The negative lens L15 is a plano-concave negative lens, the positive lens L16 is a meniscus positive lens, and the positive lens L17 is a biconvex positive lens.

[0074] In the first lens group G1, at least two positive lenses are made of flint glass; in the second lens group G2, all negative lenses in the three cemented doublets are made of flint glass, and all positive lenses in the three cemented doublets are made of crown glass. Using two achromatic cemented lens groups, each composed of positive-power crown glass and negative-power flint glass, can effectively correct chromatic aberration caused by a wide spectrum. Optionally, when the cemented doublet consists of two positive lenses, both can also be made of crown glass. In the third lens group G3, at least one positive lens is made of crown glass; and in the fourth lens group G4, at least one negative lens is made of flint glass.

[0075] In this embodiment, the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a dual telecentric optical path on both the object and image sides. The principal rays of each field of view on the object side are incident on the front surface of the first lens (meniscus lens L1) approximately parallel to the optical axis. On the object side, the principal rays of each field of view on the object plane (OBJ) are incident on the first lens (meniscus lens L1) parallel to the optical axis, with an angle less than 5 mrad between the principal rays and the optical axis. On the image side, the principal rays of each field of view exit approximately parallel to the optical axis, forming an image on the image plane (IMA), with an angle less than 2 mrad between the image and the optical axis. Therefore, both the object and image sides exhibit relatively small telecentricity.

[0076] The large field-of-view imaging objective provided in this embodiment has an object-side working distance greater than 45mm, which can meet the working distance requirements of other components in the objective application scenario. The total length of the objective is less than or equal to 1100mm, suitable for a wide spectrum of 450-650nm with a magnification of -20x, an object-side numerical aperture (NA) less than or equal to 0.45, and an object-side field-of-view diameter of 4.1mm. Under the same near-diffraction-limit image quality requirements, it can achieve a longer working distance and a larger field of view among microscope imaging lenses to meet the spatial requirements of the system, and can effectively realize aberration correction for large-aperture, high-magnification, and dual-telecentric systems.

[0077] The imaging objective lens provided in this embodiment includes 18 optical elements. Among them, the illumination beam splitter R is located between the first lens group G1 and the stop stop, and is mainly used for bright-field illumination beam splitting. In addition to the illumination beam splitter R, the remaining 17 optical elements include four cemented doublets and the rest are spherical single lenses.

[0078] Specifically, Table 1 provides the specific design values ​​for the imaging objective lens provided in this embodiment. The radius column indicates the radius of curvature of the lens; a positive radius means the center of curvature is on the right side of the surface, and a negative radius means the center of curvature is on the left side. "Infinity" indicates that the surface is flat. In the table, OBJ represents the object plane, STOP represents the aperture stop, and IMA represents the image plane. The surface numbering starts from the light incident end. The filling gas between the lenses is air. The values ​​in the material column indicate that the lens is a virtual material; the values ​​represent the refractive index and Abbe number. "Air" represents the air gap between lenses, and the filling gas is air. The thickness / gap column in the table represents the air gap or lens thickness. Lens thickness or the gap between two lenses refers to the axial distance from this surface to the next surface. All dimensions are in millimeters (mm).

[0079]

[0080]

[0081] In actual operation, the specific parameters of each lens can be adjusted and optimized according to the size of the numerical aperture to meet different system parameter requirements. Specifically, based on the current embodiment, if the working distance is small, the objective lens can meet the design requirements of a larger field of view and a larger aperture, and the overall length of the objective lens can be reduced; if the field of view is reduced, it can meet the design requirements of a larger aperture and higher resolution; if the aperture is reduced, it can meet the design requirements of a wider field of view. That is, the optical structure of the imaging objective lens provided in this embodiment can adapt to the application needs of various parameters.

[0082] Figure 2 This is a plot of the transfer function (MTF) of the imaging objective optical system provided in this embodiment. The horizontal axis represents the spatial frequency, and the vertical axis represents the MTF value. Figure 2 It can be seen that the imaging objective provided in this embodiment has a field of view close to the diffraction limit, indicating that the wavefront aberration of the objective is well corrected.

[0083] Figure 3 This is a diagram showing the astigmatism and distortion of the imaging objective lens in this embodiment. It can be seen from the diagram that the distortion at each object-side field of view is less than 0.03%, and the field curvature and astigmatism are also corrected to a very small range.

[0084] Furthermore, the imaging objective lens provided in this embodiment has a resolution of MTF > 0.42 @ 37 lp / mm. The depth of field is + / - 2.25 μm, MTF > 0.2 @ 37 lp / mm, and the total lens length is less than 1100 mm. The objective lens provided by this invention is suitable for a wide spectral range of 450-650 nm.

[0085] Example 2

[0086] Figure 4 This is an optical structure diagram of the large field-of-view imaging objective provided in this embodiment, with reference to... Figure 4 As shown, the large field-of-view imaging objective provided by the present invention includes: a first lens group G1 with positive optical power, an illumination beam splitter R, an aperture stop, a second lens group G2 with positive optical power, a third lens group G3 with negative optical power, and a fourth lens group G4 with positive optical power, arranged sequentially along the incident direction of the light beam (from the object plane to the image plane IMA). The first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship:

[0087] 0.1 < |f1 / f2| < 0.5

[0088] 3<|f2 / f3|<8

[0089] 0.1 < |f3 / f4| < 0.5

[0090] 0.1 < |f1 / f4| < 1

[0091] Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4.

[0092] Specifically, the first lens group G1 consists of two lenses, namely a positive lens L1 and a positive lens L2, which are arranged sequentially along the incident direction of the light beam. For example, the positive lens L1 is a meniscus positive lens and the positive lens L2 is a biconvex positive lens.

[0093] The second lens group G2 consists of 11 lenses, arranged sequentially along the incident direction of the light beam as follows: a cemented triplet lens group G2-1 with negative optical power consisting of positive lens L3, lens L4, lens L5 and lens L6; a cemented doublet lens group G2-2 with positive optical power consisting of lens L7 and lens L8; a cemented doublet lens group G2-3 with positive optical power consisting of negative lens L9, negative lens L10 and positive lens L11; and a cemented doublet lens group G2-4 with positive optical power consisting of lens L12 and lens L13. Among them, lens L4 and lens L6 are negative lenses, lens L5, lens L7, lens L11 and lens L12 are positive lenses, lens L8 is either a positive or negative lens, lens L10 is either a positive or negative lens, and lens L13 is either a positive or negative lens. For example, the positive lens L3 is a plano-convex positive lens, the lenses L4, L6 and L13 are biconcave negative lenses, the lens L5 is a biconvex positive lens, the lenses L7, L11 and L12 are biconvex positive lenses, the lenses L8 and L10 are meniscus negative lenses, and the negative lens L9 is a meniscus negative lens.

[0094] The third lens group consists of four lenses, arranged sequentially along the incident direction of the light beam: a cemented doublet lens group G3-1 with negative optical power composed of lens L14 and lens L15, a negative lens L16, and a negative lens L17. Lens L14 is a negative lens, and lens L15 is a positive lens. For example, lens L14 is a biconvex-concave lens, lens L15 is a biconvex positive lens, negative lens L16 is a meniscus negative lens, and negative lens L17 is a biconvex-concave lens.

[0095] The fourth lens group consists of three lenses, which are, in order, a negative lens L18, a positive lens L19, and a positive lens L20 along the incident direction of the light beam. For example, the negative lens L18 is a plano-concave negative lens, the positive lens L19 is a meniscus positive lens, and the positive lens L20 is a biconvex positive lens.

[0096] In the first lens group G1, at least two positive lenses are made of flint glass; in the second lens group G2, at least one negative lens in the cemented triplet lens group is made of flint glass; in the second lens group G2, all negative lenses in the cemented doublet lens group are made of flint glass, and all positive lenses are made of crown glass; or in the second lens group G2, both lenses in the cemented doublet lens group are made of flint glass; in the third lens group G3, at least one negative lens is made of flint glass; and in the fourth lens group G4, at least one negative lens is made of flint glass.

[0097] In this embodiment, the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 constitute a dual telecentric optical path on both the object and image sides. The principal rays of each field of view on the object side are incident on the front surface of the first lens (meniscus lens L1) approximately parallel to the optical axis. On the object side, the principal rays of each field of view on the object plane (OBJ) are incident on the first lens (meniscus lens L1) parallel to the optical axis, with an angle less than 5 mrad between the principal rays and the optical axis. On the image side, the principal rays of each field of view exit approximately parallel to the optical axis, forming an image on the image plane (IMA), with an angle less than 2 mrad between the image and the optical axis. Therefore, both the object and image sides exhibit relatively small telecentricity.

[0098] The large field-of-view imaging objective provided in this embodiment has an object-side working distance greater than 45mm, which can meet the working distance requirements of other components in the objective application scenario. The total length of the objective is less than or equal to 1100mm, suitable for a wide spectrum of 450-650nm with a magnification of -20x, an object-side numerical aperture (NA) less than or equal to 0.45, and an object-side field-of-view diameter of 4.1mm. Under the same near-diffraction-limit image quality requirements, it can achieve a longer working distance and a larger field of view among microscope imaging lenses to meet the spatial requirements of the system, and can effectively realize aberration correction for large-aperture, high-magnification, and dual-telecentric systems.

[0099] The imaging objective lens provided in this embodiment contains 21 optical elements. Among them, the illumination beam splitter R is located between the first lens group G1 and the stop stop, and is mainly used for bright-field illumination beam splitting. In addition to the illumination beam splitter R, the remaining 20 optical elements include four cemented doublets and the rest are spherical single lenses.

[0100] Specifically, Table 1 provides the specific design values ​​for the imaging objective lens provided in this embodiment. The radius column indicates the radius of curvature of the lens; a positive radius means the center of curvature is on the right side of the surface, and a negative radius means the center of curvature is on the left side. "Infinity" indicates that the surface is flat. In the table, OBJ represents the object plane, STOP represents the aperture stop, and IMA represents the image plane. The surface numbering starts from the light incident end. The filling gas between the lenses is air. The values ​​in the material column indicate that the lens is a virtual material; the values ​​represent the refractive index and Abbe number. "Air" represents the air gap between lenses, and the filling gas is air. The thickness / gap column in the table represents the air gap or lens thickness. Lens thickness or the gap between two lenses refers to the axial distance from this surface to the next surface. All dimensions are in millimeters (mm).

[0101]

[0102]

[0103] In actual operation, the specific parameters of each lens can be adjusted and optimized according to the size of the numerical aperture to meet different system parameter requirements. Specifically, based on the current embodiment, if the working distance is small, the objective lens can meet the design requirements of a larger field of view and a larger aperture, and the overall length of the objective lens can be reduced; if the field of view is reduced, it can meet the design requirements of a larger aperture and higher resolution; if the aperture is reduced, it can meet the design requirements of a wider field of view. That is, the optical structure of the imaging objective lens provided in this embodiment can adapt to the application needs of various parameters.

[0104] Figure 5 This is a plot of the transfer function (MTF) of the imaging objective optical system provided in this embodiment. The horizontal axis represents the spatial frequency, and the vertical axis represents the MTF value. Figure 5 It can be seen that the imaging objective provided in this embodiment has a field of view close to the diffraction limit, indicating that the wavefront aberration of the objective is well corrected.

[0105] Figure 6 This is a diagram showing the astigmatism and distortion of the imaging objective lens in this embodiment. It can be seen from the diagram that the distortion at each object-side field of view is less than 0.05%, and the field curvature and astigmatism are also corrected to a very small range.

[0106] Furthermore, the imaging objective lens provided in this embodiment has a resolution of MTF > 0.42 @ 37 lp / mm. The depth of field is + / - 2.25 μm, MTF > 0.2 @ 37 lp / mm, and the total lens length is less than 1100 mm. The objective lens provided by this invention is suitable for a wide spectral range of 450-650 nm.

[0107] In summary, the large field-of-view imaging objective provided by this invention employs a dual telecentric optical structure composed of lens groups with positive, positive, negative, and positive optical powers sequentially along the beam incident direction. The total objective length is ≤1100mm, suitable for a wide spectrum of 450-650nm, with a magnification of -20x, an object-side numerical aperture (NA) ≤0.45, and an object-side field-of-view diameter of 4.1mm. The imaging objective provided by this invention features a large aperture and a wide field of view, improving the objective's resolution and increasing yield. Furthermore, the imaging objective has a large numerical aperture angle and a small depth-of-field range, making it suitable for detecting different patterns on wafer surfaces. It provides sharper imaging of pit edges, meeting the wafer defect detection requirements of new processes.

Claims

1. A large field-of-view imaging objective lens, characterized in that, include: A first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 are sequentially arranged along the incident direction of the light beam. The first lens group G1 is used to converge large-angle light beams; the second lens group G2 is used to correct aberrations of the imaging objective lens; the third lens group G3 is used to magnify the real image formed by the first lens group G1 and the second lens group G2 into a virtual image to achieve high magnification, and is also used to correct field curvature; the fourth lens group G4 is used to form a real image from the virtual image generated by the third lens group G3. The first lens group G1, the second lens group G2 and the fourth lens group G4 have positive optical power, and the third lens group G3 has negative optical power. The first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship: 0.1 < |f1 / f2| < 0.5 3<|f2 / f3|<8 0.1 < |f3 / f4| < 0.5 0.1 < |f1 / f4| < 1 Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4. The first lens group G1 consists of two lenses, namely positive lens L1 and positive lens L2, which are arranged sequentially along the incident direction of the light beam. The second lens group G2 consists of 9 lenses, which are arranged in sequence along the incident direction of the light beam as follows: positive lens L3, lens L4 and lens L5 forming a cemented doublet lens group G2-1 with negative optical power; positive lens L6, negative lens L7, lens L8 and lens L9 forming a cemented doublet lens group G2-2 with negative optical power; and lens L10 and lens L11 forming a cemented doublet lens group G2-3 with positive optical power. The third lens group G3 consists of 3 lenses, which are arranged sequentially along the incident direction of the light beam as a doublet lens group G3-1 with positive optical power, composed of lens L12 and lens L13, and a negative lens L14. The fourth lens group G4 consists of three lenses, which are, in order, a negative lens L15, a positive lens L16, and a positive lens L17 along the incident direction of the light beam.

2. The large field-of-view imaging objective lens according to claim 1, characterized in that, Lens L4 and L8 are negative lenses, lens L5, lens L9 and lens L10 are positive lenses, lens L11 is either a positive or negative lens, lens L12 is either a positive or negative lens, and lens L13 is a positive lens.

3. The large field-of-view imaging objective lens according to claim 2, characterized in that, At least two positive lenses in the first lens group G1 are made of flint glass. In the second lens group G2, the negative lenses in the cemented doublet are all made of flint glass, and the positive lenses in the cemented doublet are all made of crown glass, or both lenses in the cemented doublet are made of crown glass. At least one positive lens in the third lens group G3 is made of crown glass. At least one negative lens in the fourth lens group G4 is made of flint glass.

4. A large field-of-view imaging objective lens, characterized in that, include: A first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 are sequentially arranged along the incident direction of the light beam. The first lens group G1 is used to converge large-angle light beams; the second lens group G2 is used to correct aberrations of the imaging objective lens; the third lens group G3 is used to magnify the real image formed by the first lens group G1 and the second lens group G2 into a virtual image to achieve high magnification, and is also used to correct field curvature; the fourth lens group G4 is used to form a real image from the virtual image generated by the third lens group G3. The first lens group G1, the second lens group G2 and the fourth lens group G4 have positive optical power, and the third lens group G3 has negative optical power. The first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 satisfy the following relationship: 0.1 < |f1 / f2| < 0.5 3<|f2 / f3|<8 0.1 < |f3 / f4| < 0.5 0.1 < |f1 / f4| < 1 Wherein, f1 is the focal length of the first lens group G1, f2 is the focal length of the second lens group G2, f3 is the focal length of the third lens group G3, and f4 is the focal length of the fourth lens group G4. The first lens group G1 consists of two lenses, namely positive lens L1 and positive lens L2, which are arranged sequentially along the incident direction of the light beam. The second lens group G2 consists of 11 lenses, which are arranged in the following order along the incident direction of the light beam: G2-1, a cemented triplet lens group with negative optical power composed of positive lens L3, lens L4, lens L5 and lens L6; G2-2, a cemented doublet lens group with positive optical power composed of lens L7 and lens L8; G2-3, a cemented doublet lens group with positive optical power composed of negative lens L9, negative lens L10 and positive lens L11; and G2-4, a cemented doublet lens group with positive optical power composed of lens L12 and lens L13. The third lens group consists of four lenses, which are, in sequence along the incident direction of the light beam, a doublet lens group G3-1 with negative optical power composed of lens L14 and lens L15, negative lens L16 and negative lens L17. The fourth lens group consists of three lenses, which are, in order, a negative lens L18, a positive lens L19, and a positive lens L20 along the incident direction of the light beam.

5. The large field-of-view imaging objective lens according to claim 4, characterized in that, Lens L4, L6, and L14 are negative lenses; lens L5, L7, L11, L12, and L15 are positive lenses; lens L8 is either a positive or negative lens; lens L10 is either a positive or negative lens; and lens L13 is either a positive or negative lens.

6. The large field-of-view imaging objective lens according to claim 5, characterized in that, At least two positive lenses in the first lens group G1 are made of flint glass. In the second lens group G2, the negative lenses in the cemented doublet lens group are all made of flint glass, the positive lenses in the cemented doublet lens group are all made of crown glass, or both lenses in the cemented doublet lens group are made of crown glass, and at least one negative lens in the triplet lens group is made of flint glass. At least one negative lens in the third lens group G3 is made of flint glass. At least one negative lens in the fourth lens group G4 is made of flint glass.

7. The large field-of-view imaging objective according to claim 1 or 4, characterized in that, An illumination beam splitter and an aperture are sequentially arranged between the first lens group G1 and the second lens group G2.

8. The large field-of-view imaging objective according to claim 1 or 4, characterized in that, The large field-of-view imaging objective has an object-side working distance >45mm and distortion less than 0.5%.

9. The large field-of-view imaging objective lens according to claim 1 or 4, characterized in that, The large field-of-view imaging objective has a total lens length of less than 1100mm, an object-side numerical aperture (NA) of less than or equal to 0.45, and a magnification of -20x.

10. The large field-of-view imaging objective according to claim 1 or 4, characterized in that, The diameter of the object-side field of view is 4.1 mm.

11. The large field-of-view imaging objective according to claim 1 or 4, characterized in that, The wide field-of-view imaging objective is suitable for the 450-650nm spectrum.

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