Objective lens for wafer surface defect detection

Abstract

The invention discloses an objective lens for wafer surface defect detection, and relates to the technical field of optical devices, the objective lens comprises three lens groups which are sequentially arranged according to the light incident direction, and the focal powers are respectively positive, negative and positive; the first lens group comprises a first lens with positive focal power, a second lens with negative focal power and a third lens with positive focal power, and the second lens group comprises a fourth lens with positive focal power and a fifth lens with negative focal power. The third lens group comprises a sixth lens with negative focal power, a seventh lens with positive focal power and an eighth lens with positive focal power, and the objective lens formed by arranging the lenses can correct various imaging differences, especially distortion, field curvature, astigmatism, axial chromatic aberration and chromatic aberration of magnification in the process of wafer detection imaging, so that the imaging quality is improved. The high resolution ratio and the large view field are achieved, the view field reaches 40 mm, the theoretical resolution ratio sigma is 3 microns, and the wafer detection efficiency can be greatly improved.

Description

Technical Field

[0001] This invention relates to the field of optical device technology, and more specifically to an objective lens for detecting defects on the surface of wafers. Background Technology

[0002] Semiconductor wafer defect inspection refers to the process of detecting physical defects on the wafer surface, such as particles, scratches, and bumps, as well as pattern defects, such as broken lines and short circuits in circuit patterns, during semiconductor manufacturing. With the increasing demand for integrated circuit inspection, the requirements for the efficiency of inspection systems are also constantly increasing.

[0003] With the advancement of semiconductor device manufacturing processes, devices are becoming increasingly miniaturized, and wafer defects are becoming even smaller. Currently, the optical lenses that can detect tiny wafer defects typically increase the magnification. However, the larger the magnification, the smaller the field of view. Under such limited field of view conditions, the detection efficiency of wafer defects is greatly reduced. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide an objective lens for wafer surface defect detection, aiming to solve the above-mentioned problems described in the prior art.

[0005] The first aspect of the present invention is to provide an objective lens for detecting defects on the surface of a wafer, the objective lens comprising a lens group, the lens group comprising a first lens group with positive optical power, a second lens group with negative optical power and a third lens group with positive optical power arranged sequentially from the light emission direction; The first lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, arranged in sequence according to the direction of light incidence. The second lens group includes a fourth lens with positive optical power and a fifth lens with negative optical power arranged in sequence according to the direction of light incidence; The third lens group includes a sixth lens with negative optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power, arranged in sequence according to the direction of light incidence. In this configuration, the first lens group receives the light source and refracts it to the second lens group, the second lens group collects the light emitted from the first lens group and refracts it to the third lens group, the third lens group collects the light emitted from the second lens group and focuses the light onto the surface of the wafer, and all lenses in the objective lens are on the same optical axis, with the aperture stop located in front of the first lens.

[0006] According to one aspect of the above technical solution, the objective lens has a bandwidth of 456nm±5nm, a numerical aperture (NA) of 0.095, an object-side field of view (Φ) of 40mm, a theoretical resolution (σ) of 3μm, and each lens in each lens group of the objective lens is coated with an anti-reflection coating of equal bandwidth.

[0007] According to one aspect of the above technical solution, the magnification β of the objective lens is -1x; the first lens group is used to receive light emitted by the light source through the tube lens with a focal length of 180mm.

[0008] According to one aspect of the above technical solution, the first lens in the first lens group is a meniscus lens facing the wafer, the second lens is a meniscus lens facing the wafer, and the third lens is a meniscus lens facing the wafer.

[0009] According to one aspect of the above technical solution, the second lens and the third lens are combined to form a cemented lens group.

[0010] According to one aspect of the above technical solution, the fourth lens in the second lens group is a meniscus lens facing the wafer, and the fifth lens is a biconcave lens.

[0011] According to one aspect of the above technical solution, the sixth lens in the third lens group is a meniscus lens facing the light source, the seventh lens is a meniscus lens facing the light source, and the eighth lens is a biconvex lens.

[0012] According to one aspect of the above technical solution, the refractive index of the first lens is 1.78~1.85, the refractive index of the second lens is 1.71~1.77, and the refractive index of the third lens is 1.53~1.60; The refractive index of the fourth lens is 1.61~1.67, and the refractive index of the fifth lens is 1.49~1.54; The refractive index of the sixth lens is 1.59~1.64, the refractive index of the seventh lens is 1.61~1.65, and the refractive index of the eighth lens is 1.65~1.71.

[0013] According to one aspect of the above technical solution, the Abbe number of the first lens is 35.4~45.3, the Abbe number of the second lens is 27.1~35.2, and the Abbe number of the third lens is 52.4~62.3; The Abbe number of the fourth lens is 52.5 to 59.1, and the Abbe number of the fifth lens is 54.6 to 63.2. The Abbe number of the sixth lens is 34.4 to 46.8, the Abbe number of the seventh lens is 60.8 to 69.5, and the Abbe number of the eighth lens is 52.8 to 61.9.

[0014] According to one aspect of the above technical solution, the lens in the objective lens satisfies the following relationship: 4.83 <f / epd<5.15; 0.52 <bfl / f<0.61; ttl<220mm; 6.3° <fov<6.6°; Where f is the focal length of the objective lens, epd is the entrance pupil diameter, bfl is the distance between the vertex of the rear surface of the last lens and the wafer, ttl is the distance between the object side of the first lens of the first lens group and the image plane of the objective lens, and fov is the maximum half field of view range of the objective lens.

[0015] Compared with existing technologies, the advantages of using the objective lens for wafer surface defect detection as shown in this invention are as follows: The objective lens of this invention includes three lens groups, with positive, negative, and positive optical powers, respectively. Each lens group further includes multiple lenses. The first lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, arranged in order of the light incident direction. The second lens group includes a fourth lens with positive optical power and a fifth lens with negative optical power, arranged in order of the light incident direction. The third lens group includes a sixth lens with negative optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power, arranged in order of the light incident direction. The objective lens constructed using the above lens arrangement can correct various imaging aberrations, especially distortion, field curvature, astigmatism, axial chromatic aberration, and magnification chromatic aberration, during wafer inspection imaging. It has high resolution and a large field of view, reaching 40mm, with a theoretical resolution σ of 3μm, which can significantly improve wafer inspection efficiency. Attached Figure Description

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the structure of an objective lens for wafer surface defect detection provided in an embodiment of the present invention; Figure 2 The theoretical MTF curve of the objective lens for wafer surface defect detection provided in this embodiment of the invention; Figure 3 The theoretical field curve (left) and F-tan (Theta) distortion curve (right) of the objective lens for wafer surface defect detection provided in this embodiment of the invention. Explanation of reference numerals in the attached figures: First lens group G1, second lens group G2, third lens group G3, first lens L1, second lens L2, third lens L3, fourth lens L4, fifth lens L5, sixth lens L6, seventh lens L7, eighth lens L8. Detailed Implementation

[0017] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0018] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0020] Please see Figure 1 The image shows a schematic diagram of an objective lens for detecting defects on a wafer surface provided in an embodiment of the present invention. The objective lens includes a lens group, which includes a first lens group G1 with positive optical power, a second lens group G2 with negative optical power, and a third lens group G3 with positive optical power arranged sequentially from the light emission direction. The first lens group G1 includes a first lens L1 with positive optical power, a second lens L2 with negative optical power, and a third lens L3 with positive optical power, arranged in order according to the direction of light incident. The second lens group G2 includes a fourth lens L4 with positive optical power and a fifth lens L5 with negative optical power arranged in sequence according to the direction of light incidence. The third lens group G3 includes a sixth lens L6 with negative optical power, a seventh lens L7 with positive optical power, and an eighth lens L8 with positive optical power, arranged in sequence according to the direction of light incidence. In this system, the first lens group G1 receives the light source and refracts it to the second lens group G2. The second lens group G2 collects the light emitted from the first lens group G1 and refracts it to the third lens group G3. The third lens group G3 collects the light emitted from the second lens group G2 and focuses the light onto the surface of the wafer. All lenses in the objective lens are on the same optical axis, and the aperture stop is located in front of the first lens L1.

[0021] The objective lens has a bandwidth of 456nm±5nm, the material is shown in Table 1, the numerical aperture NA is 0.095, the object-side field of view Φ is 40mm, the theoretical resolution σ is 3μm, and each lens in each lens group of the objective lens is coated with an anti-reflection coating of the same bandwidth.

[0022] The magnification β of the objective lens is -1x, i.e., equal magnification; the first lens group G1 is used to receive light emitted by the light source through the tube lens with a focal length of 180mm.

[0023] In a preferred embodiment, the first lens L1 in the first lens group G1 is a meniscus lens facing the wafer, the second lens L2 is a meniscus lens facing the wafer, and the third lens L3 is a meniscus lens facing the wafer. Furthermore, the second lens L2 and the third lens L3 together constitute a cemented lens group.

[0024] In a preferred embodiment, the fourth lens L4 in the second lens group G2 is a meniscus lens facing the wafer, and the fifth lens L5 is a biconcave lens.

[0025] In a preferred embodiment, the sixth lens L6 in the third lens group G3 is a meniscus lens facing the light source, the seventh lens L7 is a meniscus lens facing the light source, and the eighth lens L8 is a biconvex lens.

[0026] In one specific embodiment, the refractive index of the first lens L1 is 1.78~1.85, the refractive index of the second lens L2 is 1.71~1.77, and the refractive index of the third lens L3 is 1.53~1.60; The refractive index of the fourth lens L4 is 1.61~1.67, and the refractive index of the fifth lens L5 is 1.49~1.54; The refractive index of the sixth lens L6 is 1.59~1.64, the refractive index of the seventh lens L7 is 1.61~1.65, and the refractive index of the eighth lens L8 is 1.65~1.71.

[0027] In the objective lens shown, each lens in each lens group satisfies the following relationship: 1.78 <n11<1.85; 1.71 <n12<1.77; 1.53 <n13<1.60; 1.61 <n21<1.67; 1.49 <n22<1.54; 1.59 <n31<1.64; 1.61 <n32<1.65; 1.65 <n33<1.71; Wherein, n11 is the refractive index of the first lens L1 in the first lens group G1, n12 is the refractive index of the second lens L2 in the first lens group G1, n13 is the refractive index of the third lens L3 in the first lens group G1, n21 is the refractive index of the fourth lens L4 in the second lens group G2, n22 is the refractive index of the fifth lens L5 in the second lens group G2, n31 is the refractive index of the sixth lens L6 in the third lens group G3, n32 is the refractive index of the seventh lens L7 in the third lens group G3, and n33 is the refractive index of the eighth lens L8 in the third lens group G3.

[0028] In one specific embodiment, the Abbe number of the first lens is 35.4 to 45.3, the Abbe number of the second lens is 27.1 to 35.2, and the Abbe number of the third lens is 52.4 to 62.3. The Abbe number of the fourth lens is 52.5 to 59.1, and the Abbe number of the fifth lens is 54.6 to 63.2. The Abbe number of the sixth lens is 34.4 to 46.8, the Abbe number of the seventh lens is 60.8 to 69.5, and the Abbe number of the eighth lens is 52.8 to 61.9.

[0029] In the objective lens shown, each lens in each lens group satisfies the following relationship: 35.4 <v11<45.3; 27.1 <v12<35.2; 52.4 <v13<62.3; 52.5 <v21<59.1; 54.6 <v22<63.2; 34.4 <v31<46.8; 60.8 <v32<69.5; 52.8 <v33<61.9; Wherein, v11 is the Abbe number of the first lens L1 in the first lens group G1, v12 is the Abbe number of the second lens L2 in the first lens group G1, v13 is the Abbe number of the third lens L3 in the first lens group G1, v21 is the Abbe number of the fourth lens L4 in the second lens group G2, v22 is the Abbe number of the fifth lens L5 in the second lens group G2, v31 is the Abbe number of the sixth lens L6 in the third lens group G3, v32 is the Abbe number of the seventh lens L7 in the third lens group G3, and v33 is the Abbe number of the eighth lens L8 in the third lens group G3.

[0030] Furthermore, the lenses in the objective lens also satisfy the following relationship: 4.83 <f / epd<5.15; 0.52 <bfl / f<0.61; ttl<220mm; 6.3° <fov<6.6°; Where f is the focal length of the objective lens, epd is the entrance pupil diameter, bfl is the distance between the vertex of the rear surface of the last lens and the wafer, ttl is the distance between the object side of the first lens of the first lens group and the image plane of the objective lens, and fov is the maximum half field of view range of the objective lens.

[0031] In an embodiment of the present invention, the image-side numerical aperture NA of the lens is 0.095. According to the formula σ=(Kλ) / NA, K is taken as 0.61. The theoretical resolution σ of this lens can reach 3μm (K is a process coefficient factor), and the field of view reaches 40mm. During assembly, the air gaps between each lens and the thickness of the lens need to be finely adjusted to adjust the image quality deviation caused by surface processing, so as to ensure that the imaging quality of the objective lens reaches the optimal level.

[0032] The material and specific parameters of the lens in the objective lens used for wafer surface defect detection in this embodiment are shown in Table 1.

[0033] Table 1

[0034] As can be seen from Table 1, after implementing this embodiment according to the above scheme, the image quality of the objective lens is close to the theoretical calculation result.

[0035] like Figure 2 As shown, the theoretical MTF curve of the objective lens obtained by simulation analysis using the software ZEMAX is close to the diffraction limit.

[0036] like Figure 3As shown, the theoretical field curvature (left) and F-tan (Theta) distortion curve (right) of the objective lens were obtained through simulation analysis using the software ZEMAX. The meridional field curvature of the objective lens is less than 0.0067 mm, the sagittal field curvature is less than 0.0073 mm, and the maximum distortion is approximately 0.0234%.

[0037] In summary, the objective lens shown in this embodiment includes three lens groups, with positive, negative, and positive optical powers, respectively. Each lens group further includes multiple lenses. The first lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, arranged in order of the light incident direction. The second lens group includes a fourth lens with positive optical power and a fifth lens with negative optical power, arranged in order of the light incident direction. The third lens group includes a sixth lens with negative optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power, arranged in order of the light incident direction. The objective lens constructed using the above lens arrangement can correct various imaging aberrations during wafer inspection imaging, especially distortion, field curvature, astigmatism, axial chromatic aberration, and magnification chromatic aberration. It has high resolution and a large field of view, reaching 40mm, with a theoretical resolution σ of 3μm, which can significantly improve wafer inspection efficiency.

[0038] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. An objective lens for detecting defects on the surface of a wafer, the objective lens comprising a lens group, characterized in that, The lens group includes a first lens group with positive optical power, a second lens group with negative optical power, and a third lens group with positive optical power, arranged sequentially from the direction of light emission. The first lens group includes a first lens with positive optical power, a second lens with negative optical power, and a third lens with positive optical power, arranged in sequence according to the direction of light incidence. The second lens group includes a fourth lens with positive optical power and a fifth lens with negative optical power arranged in sequence according to the direction of light incidence; The third lens group includes a sixth lens with negative optical power, a seventh lens with positive optical power, and an eighth lens with positive optical power, arranged in sequence according to the direction of light incidence. In this configuration, the first lens group receives the light source and refracts it to the second lens group, the second lens group collects the light emitted from the first lens group and refracts it to the third lens group, the third lens group collects the light emitted from the second lens group and focuses the light onto the surface of the wafer, and all lenses in the objective lens are on the same optical axis, with the aperture stop located in front of the first lens.

2. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The objective lens has a bandwidth of 456nm±5nm, a numerical aperture (NA) of 0.095, an object-side field of view (Φ) of 40mm, and a theoretical resolution (σ) of 3μm. Furthermore, each lens in each lens group of the objective lens is coated with an anti-reflection coating of equal bandwidth.

3. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The magnification β of the objective lens is -1x; the first lens group is used to receive light emitted by the light source through the tube lens with a focal length of 180mm.

4. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The first lens in the first lens group is a meniscus lens facing the wafer, the second lens is a meniscus lens facing the wafer, and the third lens is a meniscus lens facing the wafer.

5. The objective lens for wafer surface defect detection according to claim 4, characterized in that, The second lens and the third lens together form a cemented lens group.

6. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The fourth lens in the second lens group is a meniscus lens facing the wafer, and the fifth lens is a biconcave lens.

7. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The sixth lens in the third lens group is a meniscus lens facing the light source, the seventh lens is a meniscus lens facing the light source, and the eighth lens is a biconvex lens.

8. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The first lens has a refractive index of 1.78 to 1.85, the second lens has a refractive index of 1.71 to 1.77, and the third lens has a refractive index of 1.53 to 1.

60. The refractive index of the fourth lens is 1.61~1.67, and the refractive index of the fifth lens is 1.49~1.54; The refractive index of the sixth lens is 1.59~1.64, the refractive index of the seventh lens is 1.61~1.65, and the refractive index of the eighth lens is 1.65~1.

71.

9. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The Abbe number of the first lens is 35.4 to 45.3, the Abbe number of the second lens is 27.1 to 35.2, and the Abbe number of the third lens is 52.4 to 62.

3. The Abbe number of the fourth lens is 52.5 to 59.1, and the Abbe number of the fifth lens is 54.6 to 63.

2. The Abbe number of the sixth lens is 34.4 to 46.8, the Abbe number of the seventh lens is 60.8 to 69.5, and the Abbe number of the eighth lens is 52.8 to 61.

9.

10. The objective lens for wafer surface defect detection according to claim 1, characterized in that, The lenses in the objective lens satisfy the following relationship: 4.83 <f / epd<5.15; 0.52 <bfl / f<0.61; ttl<220mm; 6.3° <fov<6.6°; Where f is the focal length of the objective lens, epd is the entrance pupil diameter, bfl is the distance between the vertex of the rear surface of the last lens and the wafer, ttl is the distance between the object side of the first lens of the first lens group and the image plane of the objective lens, and fov is the maximum half field of view range of the objective lens.

Images