Wide-spectrum epi-erretinal objective

Abstract

The application discloses a wide-spectrum catadioptric objective. The wide-spectrum catadioptric objective comprises a first mirror group, a second mirror group and a third mirror group arranged in sequence along the optical axis direction; the first mirror group comprises a meniscus positive lens, a meniscus negative lens and a plano-convex lens, and the edge region of the first mirror surface of the meniscus positive lens and the second mirror surface of the meniscus negative lens is provided with a reflecting surface region; the incident light is reflected and refracted in the meniscus positive lens and the meniscus negative lens for multiple times, and then forms an intermediate image after passing through the plano-convex lens; the first mirror group has positive focal power, increases the numerical aperture and corrects aberration; the second mirror group and the third mirror group both have negative focal power; the intermediate image is emitted to an image plane in parallel light after passing through the second mirror group and the third mirror group, and satisfies 0.35<|R min / f|<1.5; f is the combined focal length of the meniscus positive lens and the meniscus negative lens, and R min is the minimum curvature radius of the reflecting surface. The wide-spectrum catadioptric objective has the characteristics of wide spectrum, high resolution, high numerical aperture, large field of view and long working distance simultaneously.

Description

Technical Field

[0001] This invention belongs to the field of optical systems, and more specifically, relates to a broadband catadioptric objective lens. Background Technology

[0002] In the field of semiconductor front-end inspection, optical and electronic systems are needed to detect defects and check for the presence of defects on the sample surface. These defects are relatively small, such as particles, scratches, process variations, and repeating patterns. This necessitates higher resolution. Especially in the ultraviolet wavelength region, the transmittance of ordinary optical materials is extremely low. With the increase in numerical aperture and field of view, refractive systems have become very difficult to design.

[0003] As the features on the sample surface become smaller and smaller, and with the use of new materials and manufacturing processes, there is a need to detect new and finer defects. The sample surface needs to be inspected quickly and efficiently as possible. Objectives with wide spectrum, high resolution, large field of view, and long working distance are difficult to design and manufacture, and few objectives can currently meet these requirements.

[0004] Existing technologies have the problem that objectives cannot simultaneously possess both high numerical aperture and a large field of view. Summary of the Invention

[0005] In view of the shortcomings of related technologies, the purpose of this invention is to provide a broadband catadioptric objective lens, which aims to solve the problem that an objective lens cannot simultaneously have a high numerical aperture and a large field of view.

[0006] To achieve the above objectives, the present invention provides a broadband catadioptric objective lens, which includes a first lens group G1, a second lens group G2, and a third lens group G3 sequentially along its optical axis from the object plane side to the image plane side.

[0007] The first lens group G1 includes a meniscus positive lens 1, a meniscus negative lens 2, and a plano-convex lens 3 arranged sequentially along the optical path. The edge region of the first mirror surface of the meniscus positive lens 1 near the object plane is provided with a reflective surface region, and the edge region of the second mirror surface of the meniscus negative lens 2 near the image plane is provided with a reflective surface region. The incident light rays are refracted through the central transmission region of the first mirror surface and reach the reflective surface region of the second mirror surface. They are then reflected back into the meniscus positive lens 1, and after being refracted again, they reach the reflective surface region of the first mirror surface. This allows the incident light rays to undergo multiple refractions in the meniscus positive lens 1 and the meniscus negative lens 2, and after passing through the plano-convex lens 3, an intermediate image is formed between the first lens group G1 and the second lens group G2.

[0008] The first lens group G1 has positive optical power and is used to increase numerical aperture and correct aberrations;

[0009] Both the second lens group G2 and the third lens group G3 have negative optical power; the intermediate image is emitted as parallel light onto the image plane after passing through the second lens group G2 and the third lens group G3.

[0010] The positive meniscus lens 1 and the negative meniscus lens 2 satisfy: 0.35 < |R min / f|<1.5; where f is the combined focal length of the meniscus positive lens 1 and the meniscus negative lens 2, and R min It is the smallest radius of curvature among the reflecting surfaces of the meniscus positive lens 1 and the meniscus negative lens 2.

[0011] Optionally, the area of ​​the central transmission region of the first mirror is 10% of the mirror area, and all areas other than the central transmission region are reflective surface areas.

[0012] The central transmission area of ​​the second mirror is 3.7% of the mirror area, and all areas outside the central transmission area are reflective areas.

[0013] Optionally, the reflective area is coated with a reflective film.

[0014] Optionally, the second lens group G2 includes a biconvex positive lens 4, a biconvex positive lens 5, and a meniscus positive lens 6 arranged sequentially along the optical path; the third lens group G3 includes a biconvex positive lens 7, a meniscus negative lens 8, a meniscus negative lens 9, and a meniscus positive lens 10 arranged sequentially along the optical path.

[0015] Optionally, all lens elements are spherical.

[0016] Optionally, all lens elements are made of non-fluorescent optical materials.

[0017] Optionally, the numerical aperture of the broadband catadioptric objective lens is greater than or equal to 0.9.

[0018] Optionally, the broadband catadioptric objective includes 10 lens elements.

[0019] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0020] 1. The present invention provides a broadband catadioptric objective lens, extending its applicability from the visible light region to the ultraviolet wavelength region, mainly located in the 360nm to 550nm band. The present invention sets reflective surface areas at the edge regions of the meniscus positive lens and meniscus negative lens in the first lens group to reflect the incident light, causing it to undergo multiple refractions in the meniscus positive lens and meniscus negative lens. The folded optical path formed in the meniscus positive lens and meniscus negative lens can effectively correct various aberrations of the system and significantly increase the numerical aperture. Thus, the broadband catadioptric objective lens simultaneously possesses the characteristics of broadband spectrum, high resolution, large field of view, and long working distance.

[0021] 2. The broadband catadioptric objective lens provided by the present invention uses lens elements with small apertures, all of which are spherical lenses; the lens elements used in the first lens group do not require the processing of light-transmitting holes in the central part of the lens, which greatly reduces the difficulty of processing, testing and calibration.

[0022] 3. The broadband catadioptric objective lens provided by this invention can achieve good correction of various aberrations of the optical system with a minimum of 10 optical elements, and has a numerical aperture of 0.9 and a field of view of 1 mm, thus having the effects of high numerical aperture and large field of view. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a broadband catadioptric objective lens provided in an embodiment of the present invention;

[0024] Figure 2 The MTF (Mean Transformer Function) plot of an optical system for a broadband catadioptric objective lens provided in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0027] A broadband catadioptric objective lens, which includes a first lens group G1, a second lens group G2, and a third lens group G3 sequentially from the object plane side to the image plane side along its optical axis.

[0028] The first lens group G1 includes a meniscus positive lens 1, a meniscus negative lens 2, and a plano-convex lens 3 arranged sequentially along the optical path. The edge region of the first mirror surface of the meniscus positive lens 1 near the object plane is provided with a reflective surface region, and the edge region of the second mirror surface of the meniscus negative lens 2 near the image plane is provided with a reflective surface region. The incident light rays are refracted through the central transmission region of the first mirror surface and reach the reflective surface region of the second mirror surface. They are then reflected back into the meniscus positive lens 1, and after being refracted again, they reach the reflective surface region of the first mirror surface. This allows the incident light rays to undergo multiple refractions in the meniscus positive lens 1 and the meniscus negative lens 2, and after passing through the plano-convex lens 3, an intermediate image is formed between the first lens group G1 and the second lens group G2.

[0029] The first lens group G1 has positive optical power and is used to increase numerical aperture and correct aberrations;

[0030] Both the second lens group G2 and the third lens group G3 have negative optical power; the intermediate image is emitted as parallel light onto the image plane after passing through the second lens group G2 and the third lens group G3.

[0031] The positive meniscus lens 1 and the negative meniscus lens 2 satisfy: 0.35 < |R min / f|<1.5;

[0032] Where f is the combined focal length of the meniscus positive lens 1 and the meniscus negative lens 2, and R min It is the smallest radius of curvature among the reflecting surfaces of the meniscus positive lens 1 and the meniscus negative lens 2.

[0033] After the light rays from the object plane pass through the reflecting mirror of the first mirror group G1, they will pass through at least one element with refractive properties and form an intermediate image after the final refractive surface. The intermediate image passes through the second mirror group G2 and the third mirror group G3 and is then emitted as parallel light onto the image plane. The characteristics of the constructed broadband catadioptric objective lens are detected by detecting the intermediate image.

[0034] In this system, the lens convex to the object plane is a meniscus positive lens, and the lens convex to the image plane is a meniscus negative lens. The first lens group G1 has two reflecting surfaces: a reflecting surface area located at the edge of the first mirror of the meniscus positive lens 1, and a reflecting surface area located at the edge of the second mirror of the meniscus negative lens 2. The incident optical fiber enters through the transmission area of ​​the first mirror of the meniscus positive lens 1, is refracted, and exits to the reflecting surface area of ​​the second mirror. After reflection, it exits from the meniscus negative lens 2, returns to the meniscus positive lens 1, is reflected again, reaches the reflecting surface area of ​​the first mirror, is reflected again, exits from the meniscus positive lens 1, and reaches the meniscus negative lens 2 again. By adjusting the size of the reflecting area and the curvature of the meniscus positive lens 1 and the meniscus negative lens 2, the number of reflections and refractions of the incident light in the first lens group G1 can be adjusted, thereby adjusting the correction of various aberrations and numerical aperture parameters of the system, achieving characteristics such as wide spectrum, high resolution, large field of view, and long working distance. In this embodiment, preferably, the incident light is reflected twice and refracted ten times in the first mirror group G1.

[0035] To ensure that as much transmitted light as possible is reflected by the reflecting surface, and that the light after multiple refractions enters the next lens group through the aperture of the meniscus negative lens 2, the combined focal length f of the meniscus positive lens 1 and the meniscus negative lens 2 satisfies: 0.35 < |R min / f|<1.5; if R min If the aperture is too small or too large, it will reduce the resolution, decrease the proportion of the light-transmitting aperture, and thus reduce the brightness.

[0036] Optionally, the area of ​​the central transmission region of the first mirror is 10% of the mirror area, and all areas other than the central transmission region are reflective surface areas.

[0037] The central transmission area of ​​the second mirror is 3.7% of the mirror area, and all areas outside the central transmission area are reflective areas.

[0038] A reflective film is deposited on the reflective areas of the first and second mirror surfaces. The selection of the reflective film needs to meet the requirements of transmittance at ultraviolet wavelengths, as well as processing cost and difficulty. In this embodiment, an ultraviolet-enhanced aluminum reflective film is preferred. Furthermore, in the broadband catadioptric objective lens provided by this invention, all lens elements are spherical, all lens elements are made of non-fluorescent optical materials, and the lens elements used have small apertures. Figure 1 The maximum aperture of the system's optical path is located at the reflecting surface of the meniscus negative lens 2, which in this embodiment is approximately 13mm. This significantly reduces the difficulty of fabricating, testing, and calibrating system components.

[0039] Based on the above embodiments, further reference is made to... Figure 1 The second lens group G2 includes a biconvex positive lens 4, a biconvex positive lens 5, and a meniscus positive lens 6 arranged sequentially along the optical path; the third lens group G3 includes a biconvex positive lens 7, a meniscus negative lens 8, a meniscus negative lens 9, and a meniscus positive lens 10 arranged sequentially along the optical path.

[0040] The broadband catadioptric objective provided in this embodiment has a numerical aperture greater than or equal to 0.9 and a total number of lens elements greater than or equal to 10. The number of lens elements can be adjusted in group G2 according to different requirements for the intermediate image position. While satisfying the functionality of the broadband catadioptric objective, minimizing the number of lens elements can reduce the size of the broadband catadioptric objective. Preferably, the broadband catadioptric objective provided in this embodiment includes 10 lens elements.

[0041] This invention provides a reflective surface at the edge of the lens element in the lens assembly and a transmission area in the middle. Incident light enters the lens from the transmission area, is refracted, and then reflected back to the reflective surface coated with a reflective film for further refraction. This allows the incident light to undergo multiple refractions through the formed folded optical path, solving the problem that objectives cannot simultaneously possess both high numerical aperture and a large field of view. This enables a broadband catadioptric objective to simultaneously possess the characteristics of a wide spectrum, high resolution, large field of view, and long working distance.

[0042] In one specific embodiment: numerical aperture NA = 0.9; object-side field of view diameter: 1 mm; wavelength range: 360 nm to 550 nm; where NA is the numerical aperture of the object side.

[0043] Among them, such as Figure 1 As shown, the first mirror group G1 contains two reflective surfaces, at least four refracting surfaces, and at least one refracting lens. Light rays emitted from the object plane pass through the first mirror group G1 and, before entering the refracting lens, pass through the at least two refracting surfaces three times within the reflecting mirror surface. In the first mirror group G1, the meniscus positive lens 1 has a reflective surface area near the edge of the first mirror surface of the object plane, and is coated with a film. 10% of the central area of ​​this surface is a transmission area, serving as the light-transmitting aperture, while the remaining portion is coated with a reflective film. The meniscus negative lens 2 has a reflective surface area near the edge of the second mirror surface of the image plane, and is coated with a film. 3.7% of the central area of ​​this surface is a transmission area, serving as the light-transmitting aperture, while the remaining portion is coated with a reflective film.

[0044] Among them, the positive meniscus lens 1 and the negative meniscus lens 2 satisfy: 0.35 < |R min / f|<1.5; f is the combined focal length of the meniscus positive lens 1 and the meniscus negative lens 2, R min It is the smallest radius of curvature among the reflecting surfaces of the meniscus positive lens (1) and the meniscus negative lens 2.

[0045] In the embodiments of this invention, the device is applicable to the 360nm to 550nm wavelength range, that is, it is applicable from the ultraviolet to the visible light range. The first lens group G1 is mainly used to increase the numerical aperture, while the second lens group G2 and the third lens group G3 are used to correct the residual aberrations of the first lens group. All lens materials are selected from optical materials with high transmittance in the 360-550nm wavelength range. Specifically, the meniscus positive lens 1 and meniscus negative lens 9 use BASF5 material, the meniscus negative lens 2 and biconvex positive lens 7 use Schott's N-series glass, the plano-convex lens 3 and biconvex positive lens 4 use Chengdu Guangming's D-series glass, the biconvex positive lens 5 uses quartz glass, the meniscus positive lens 6 uses Schott's K10 glass, the meniscus negative lens 8 uses Nikon's NIFS series glass, and the meniscus positive lens 10 uses I-line series I-PBL1Y glass. Through the combination of different materials, axial chromatic aberration can be corrected very well. After the intermediate image plane is enlarged by the third lens group, the system aperture decreases, and the angle of the emitted light rays is parallel to the outside of the system.

[0046] The optical parameters of the lens elements in the three lens groups are shown in Table 1.

[0047] Table 1 Objective lens element parameters

[0048]

[0049]

[0050] Figure 2The MTF plot of the optical system is given, based on Figure 2 It can be seen that the field of view from 0 to 0.5 is very close to the diffraction limit. Throughout the entire spectrum and the entire field of view, it is also close to the diffraction limit of physical optics. Analysis results from optical design software show that the wavefront aberration RMS in the central field of view is less than 0.06 wavelengths, and the wavefront aberration RMS in the entire field of view is less than 0.12 wavelengths. The transverse chromatic aberration is approximately 200 nm, and the second-order spectral correction is also quite good.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband catadioptric objective lens, characterized in that, The broadband catadioptric objective is applicable to the wavelength range of 360nm to 550nm. The broadband catadioptric objective includes a first lens group (G1), a second lens group (G2), and a third lens group (G3) sequentially from the object plane side to the image plane side along its optical axis. The first lens group (G1) includes a meniscus positive lens (1) with its convex surface facing the object plane, a meniscus negative lens (2) with its convex surface facing the image plane, and a plano-convex lens (3) arranged sequentially along the optical path. The meniscus positive lens (1) has a reflective surface area near the edge region of the first mirror surface close to the object plane, and the meniscus negative lens (2) has a reflective surface area near the edge region of the second mirror surface close to the image plane. The incident light is refracted through the central transmission region of the first mirror surface and reaches the reflective surface area of ​​the second mirror surface. It is reflected back into the meniscus positive lens (1), and after being refracted again, it reaches the reflective surface area of ​​the first mirror surface. Then, the incident light is refracted three times in the meniscus positive lens (1) and the meniscus negative lens (2), and after passing through the plano-convex lens (3), an intermediate image is formed between the first lens group (G1) and the second lens group (G2). The first lens group (G1) has positive optical power and is used to increase numerical aperture and correct aberrations; Both the second lens group (G2) and the third lens group (G3) have negative optical power; the intermediate image is emitted onto the image plane as parallel light after passing through the second lens group (G2) and the third lens group (G3); The positive meniscus lens (1) and the negative meniscus lens (2) satisfy: 0.35 < | R min / f | < 1.5; where, f The combined focal length of the meniscus positive lens (1) and the meniscus negative lens (2) is... R min The minimum radius of curvature of the reflecting surfaces of the positive meniscus lens (1) and the negative meniscus lens (2); The second lens group (G2) includes a biconvex positive lens (4), a biconvex positive lens (5), and a meniscus positive lens (6) with its convex surface facing the image plane, arranged sequentially along the optical path; the third lens group (G3) includes a biconvex positive lens (7), a meniscus negative lens (8) with its convex surface facing the object plane, a meniscus negative lens (9) with its convex surface facing the image plane, and a meniscus positive lens (10) with its convex surface facing the image plane, arranged sequentially along the optical path. The broadband catadioptric objective lens comprises a total of 10 lens elements.

2. The broadband catadioptric objective lens according to claim 1, characterized in that, The central transmission area of ​​the first mirror is 10% of the mirror area, and all areas outside the central transmission area are reflective areas. The central transmission area of ​​the second mirror is 3.7% of the mirror area, and all areas outside the central transmission area are reflective areas.

3. The broadband catadioptric objective lens according to claim 2, characterized in that, The reflective surface area is coated with a reflective film.

4. The broadband catadioptric objective lens according to claim 1, characterized in that, All lens elements are spherical.

5. The broadband catadioptric objective lens according to claim 1, characterized in that, All lens elements are made of non-fluorescent optical materials.

6. The broadband catadioptric objective lens according to claim 1, characterized in that, The numerical aperture of the broadband catadioptric objective lens is 0.9.

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