An objective lens for wafer surface defect detection

Abstract

The application 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 arranged in sequence according to the light incidence direction, and the optical powers of the three lens groups are positive, negative and positive respectively.The first lens group comprises a first lens with a positive optical power, a second lens with a negative optical power and a third lens with a positive optical power.The second lens group comprises a fourth lens with a positive optical power and a fifth lens with a negative optical power.The third lens group comprises a sixth lens with a negative optical power, a seventh lens with a positive optical power and an eighth lens with a positive optical power.The objective lens formed by the above lens arrangement can correct various imaging aberrations, especially distortion, field curvature, astigmatism, axial chromatic aberration and magnification chromatic aberration, has high resolution and a large field of view, and can greatly improve the detection efficiency of the wafer.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical devices, in particular to an objective lens for wafer surface defect detection. BACKGROUND

[0002] Wafer defect detection refers to a process of detecting physical defects such as particles, scratches, bumps, etc. on the surface of a wafer, as well as pattern defects such as broken lines and short circuits of a circuit pattern during the manufacturing process of a semiconductor. With the increasing demand for integrated circuit detection, the efficiency of the detection system is also constantly improving.

[0003] With the advancement of semiconductor device manufacturing processes, devices are gradually miniaturized, and the wafer defects therein are also smaller. In the related optical lens that can currently detect wafer defects, the magnification is usually increased, which results in a smaller field of view due to the large magnification. In the case of limited field of view, the detection efficiency of wafer defect detection is greatly reduced. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide an objective lens for wafer surface defect detection, which aims to solve the above-mentioned problems recorded in the prior art.

[0005] The first aspect of the present application provides an objective lens for wafer surface defect detection, the objective lens comprising a lens group, the lens group comprising a first lens group with positive focal power, a second lens group with negative focal power and a third lens group with positive focal power arranged in sequence from the direction of light exit;

[0006] 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 arranged in sequence from the direction of light incidence;

[0007] The second lens group comprises a fourth lens with positive focal power and a fifth lens with negative focal power arranged in sequence from the direction of light incidence;

[0008] 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 arranged in sequence from the direction of light incidence;

[0009] The first lens group receives a light source and refracts the light source to the second lens group, the second lens group collects the light rays emitted from the first lens group and refracts them to the third lens group, the third lens group collects the light rays emitted from the second lens group and focuses them on the surface of the wafer, and all the lenses in the objective lens are on the same optical axis, and the diaphragm is located before the first lens.

[0010] According to an aspect of the above technical solution, the bandwidth of the objective lens is 456nm±5nm, the numerical aperture NA is 0.095, the object field Φ is 40mm, the theoretical resolution σ is 3μm, and each lens in each lens group of the objective lens is coated with an equal bandwidth of anti-reflection film.

[0011] According to an aspect of the above technical solution, the magnification β of the objective lens is -1x; and the first lens group is used to receive light emitted by a light source through a tube lens with a focal length of 180mm.

[0012] According to an 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.

[0013] According to an aspect of the above technical solution, the second lens and the third lens combine to form a cemented lens group.

[0014] According to an 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 double-concave lens.

[0015] According to an 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 double-convex lens.

[0016] According to an 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;

[0017] 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;

[0018] 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.

[0019] According to an 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;

[0020] The Abbe number of the fourth lens is 52.5~59.1, and the Abbe number of the fifth lens is 54.6~63.2;

[0021] The Abbe number of the sixth lens is 34.4-46.8, the Abbe number of the seventh lens is 60.8-69.5, and the Abbe number of the eighth lens is 52.8-61.9.

[0022] According to an aspect of the above technical solution, the lenses in the objective lens satisfy the following relationship:

[0023] 4.83 < f / epd < 5.15;

[0024] 0.52 < bfl / f < 0.61;

[0025] ttl < 220mm;

[0026] 6.3° < fov < 6.6°;

[0027] Wherein, f is the focal length of the objective lens, epd is the entrance pupil diameter, bfl is the distance between the rear surface vertex of the last lens and the wafer, ttl is the distance from the object side surface of the first lens of the first lens group to the image surface of the objective lens, and fov is the maximum half field of view range of the objective lens.

[0028] Compared with the prior art, the objective lens for wafer surface defect detection provided by the application has the following beneficial effects:

[0029] The objective lens comprises three lens groups, and the optical powers of the three lens groups are positive, negative and positive respectively. Each lens group comprises a plurality of lenses. The first lens group comprises 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 incident light. The second lens group comprises a fourth lens with positive optical power and a fifth lens with negative optical power arranged in sequence according to the direction of incident light. The third lens group comprises 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 incident light. The objective lens formed by the above lens arrangement can correct various imaging aberrations, especially distortion, field curvature, astigmatism, axial chromatic aberration and magnification chromatic aberration, has high resolution and a large field of view, and has a field of view of 40mm and a theoretical resolution of sigma of 3um. The detection efficiency of the wafer can be greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the application will become apparent and more readily appreciated from the following description, taken in conjunction with the following drawings, in which:

[0031] Figure 1 The structure diagram of the objective lens for wafer surface defect detection provided in the embodiments of the application is shown in the drawings.

[0032] Figure 2Theoretical MTF curve of the objective lens for wafer surface defect detection provided in the embodiment of the present application;

[0033] Figure 3 Theoretical field curvature (left) and F-tan (Theta) distortion curve (right) of the objective lens for wafer surface defect detection provided in the embodiment of the present application;

[0034] Explanation of reference signs:

[0035] 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 DESCRIPTION

[0036] In order to make the objects, features and advantages of the present application more apparent, the specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. The present application is shown in several embodiments in the drawings. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0037] It should be noted that when an element is referred to as being "fixedly attached" to another element, it can be directly on the other element or intervening elements can also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements can also be present. The terms "vertical", "horizontal", "left", "right" and similar expressions as used herein are for illustrative purposes only.

[0038] 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 application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] Referring to Figure 1 , a structure schematic diagram of an objective lens for wafer surface defect detection provided in the embodiment of the present application is shown, the objective lens comprises a lens group, the lens group comprises a first lens group G1 with positive refractive power, a second lens group G2 with negative refractive power and a third lens group G3 with positive refractive power arranged in sequence from the light exit direction;

[0040] The first lens group G1 comprises a first lens L1 with positive refractive power, a second lens L2 with negative refractive power and a third lens L3 with positive refractive power arranged in sequence from the light incidence direction;

[0041] The second lens group G2 comprises a fourth lens L4 with positive focal power and a fifth lens L5 with negative focal power arranged in sequence according to the direction of light incidence;

[0042] The third lens group G3 comprises a sixth lens L6 with negative focal power, a seventh lens L7 with positive focal power and an eighth lens L8 with positive focal power arranged in sequence according to the direction of light incidence;

[0043] The first lens group G1 receives light source and refracts the light source to the second lens group G2, the second lens group G2 collects light rays emitted from the first lens group G1 and refracts to the third lens group G3, the third lens group G3 collects light rays emitted from the second lens group G2 and focuses the light rays on the surface of the wafer, and all lenses in the objective lens are on the same optical axis, and the diaphragm is located before the first lens L1.

[0044] The bandwidth of the objective lens is 456nm±5nm, the material is shown in Table 1, the numerical aperture NA is 0.095, the object field Φ is 40mm, the theoretical resolution σ is 3μm, and each lens in each lens group of the objective lens is coated with an antireflection film with the same bandwidth.

[0045] The magnification β of the objective lens is -1x, i.e. equal magnification; the first lens group G1 is used to receive light rays emitted by the tube lens with a focal length of 180mm.

[0046] 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 combine to form a cemented lens group.

[0047] 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 double-concave lens.

[0048] 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 double-convex lens.

[0049] In a 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;

[0050] 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;

[0051] 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.

[0052] Among the lens groups of the objective lens, each lens satisfies the following relationship:

[0053] 1.78 < n11 < 1.85;

[0054] 1.71 < n12 < 1.77;

[0055] 1.53 < n13 < 1.60;

[0056] 1.61 < n21 < 1.67;

[0057] 1.49 < n22 < 1.54;

[0058] 1.59 < n31 < 1.64;

[0059] 1.61 < n32 < 1.65;

[0060] 1.65 < n33 < 1.71;

[0061] 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.

[0062] In one specific embodiment, 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;

[0063] The Abbe number of the fourth lens is 52.5-59.1, and the Abbe number of the fifth lens is 54.6-63.2;

[0064] The Abbe number of the sixth lens is 34.4-46.8, the Abbe number of the seventh lens is 60.8-69.5, and the Abbe number of the eighth lens is 52.8-61.9.

[0065] In each lens group of the objective lens, each lens satisfies the following relationship:

[0066] 35.4 < v11 < 45.3;

[0067] 27.1 < v12 < 35.2;

[0068] 52.4 < v13 < 62.3;

[0069] 52.5 < v21 < 59.1;

[0070] 54.6 < v22 < 63.2;

[0071] 34.4 < v31 < 46.8;

[0072] 60.8 < v32 < 69.5;

[0073] 52.8 < v33 < 61.9;

[0074] 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.

[0075] In addition, the lenses in the objective lens also satisfy the following relationship:

[0076] 4.83 < f / epd < 5.15;

[0077] 0.52 < bfl / f < 0.61;

[0078] ttl < 220 mm;

[0079] 6.3° < fov < 6.6°;

[0080] wherein 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 from the object side surface of the first lens of the first lens group to the image surface of the objective lens, and fov is the maximum half field of view range of the objective lens.

[0081] In the embodiment of the present application, the lens image-side numerical aperture NA is 0.095, according to the formula σ=(Kλ) / NA, K is 0.61, the theoretical resolution σ of the lens can reach 3μm (K is a process coefficient factor), and the field of view reaches 40mm. During assembly, the air gap between lenses and the thickness of lenses need to be fine-tuned to adjust the image quality deviation caused by surface machining, so as to ensure that the imaging quality of the objective lens reaches the optimum.

[0082] The material and specific parameters of the lenses in the objective lens used for wafer surface defect detection in the embodiment are shown in Table 1.

[0083] Table 1

[0084]

[0085] As can be seen from Table 1, after implementing the embodiment according to the above scheme, the image quality of the objective lens is closer to the theoretical calculation result.

[0086] As shown in Figure 2 , the theoretical MTF curve of the objective lens obtained by software ZEMAX simulation analysis is close to the diffraction limit.

[0087] As shown in Figure 3 , the theoretical field curvature (left) and F-tan (Theta) distortion curve (right) of the objective lens obtained by software ZEMAX simulation analysis are shown, wherein the meridional field curvature of the objective lens is less than 0.0067mm, the sagittal field curvature is less than 0.0073mm, and the maximum distortion is about 0.0234%.

[0088] In summary, the objective lens shown in the embodiment includes three lens groups, the optical power of the three lens groups is positive, negative and positive respectively, each lens group includes a plurality of 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 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 order according to the direction of light incidence, and 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 according to the direction of light incidence. The objective lens formed by the above lens arrangement can correct various imaging aberrations, especially distortion, field curvature, astigmatism, axial chromatic aberration and magnification chromatic aberration, has high resolution and large field of view, the field of view reaches 40mm, the theoretical resolution σ is 3μm, and the detection efficiency of the wafer can be greatly improved.

[0089] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present 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 can be combined in any one or more embodiments or examples in a suitable manner.

[0090] The above-described embodiments only express several implementation manners of the present application, which are described in a more specific and detailed manner, but cannot be understood as a limitation on the patent scope of the present application. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An objective lens for wafer surface defect detection, the objective lens comprising a lens group, characterized by, The lens group is composed of a first lens group with positive focal power, a second lens group with negative focal power and a third lens group with positive focal power arranged in sequence according to the light exit direction; The first lens group is composed of a first lens with positive focal power, a second lens with negative focal power and a third lens with positive focal power arranged in sequence according to the light incidence direction; The second lens group is composed of a fourth lens with positive focal power and a fifth lens with negative focal power arranged in sequence according to the light incidence direction; The third lens group is composed of a sixth lens with negative focal power, a seventh lens with positive focal power and an eighth lens with positive focal power arranged in sequence according to the light incidence direction; The first lens group receives the light source and refracts the light source to the second lens group, the second lens group collects the light rays emitted from the first lens group and refracts to the third lens group, the third lens group collects the light rays emitted from the second lens group and focuses the light rays on the surface of the wafer, and all lenses in the objective lens are on the same optical axis, and the diaphragm is located before the first lens. The bandwidth of the objective lens is 456nm±5nm, the numerical aperture NA is 0.095, the object field Φ is 40mm, the theoretical resolution σ is 3μm, and each lens in each lens group of the objective lens is coated with an equal bandwidth of anti-reflection film.

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

3. The objective lens for wafer surface defect detection according to claim 1, wherein, 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.

4. The objective lens for wafer surface defect detection according to claim 3, wherein, The second lens and the third lens combine to form a cemented lens group.

5. The objective lens for wafer surface defect detection according to claim 1, wherein, The fourth lens in the second lens group is a meniscus lens facing the wafer, and the fifth lens is a double concave lens.

6. The objective lens for wafer surface defect detection according to claim 1, wherein, 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 double convex lens.

7. The objective lens for wafer surface defect detection according to claim 1, wherein, 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.

8. The objective lens for wafer surface defect detection according to claim 1, wherein, 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 52.5~59.1, and the Abbe number of the fifth lens is 54.6~63.2; The Abbe number of the sixth lens is 34.4~46.8, the Abbe number of the seventh lens is 60.8~69.5, and the Abbe number of the eighth lens is 52.8~61.

9.

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

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