A deep ultraviolet catadioptric test objective

Abstract

The application discloses a deep ultraviolet spherical catadioptric detection objective lens and relates to the technical field of optics.The deep ultraviolet spherical catadioptric detection objective lens comprises a first lens group, a second lens group and a diaphragm, one side of the first lens group is provided with an object plane, the first lens group is located between the second lens group and the object plane, the first lens group is used for converging light rays and correcting residual aberration of the second lens group, the diaphragm is arranged in the middle of the second lens group, and the second lens group and the diaphragm are used for correcting coma and other vertical axial aberrations of the system.The objective lens adopts a spherical catadioptric structure, can realize deep ultraviolet wave band application, has a large numerical aperture, the numerical aperture can reach 0.8, a shorter wavelength, a larger numerical aperture and higher resolution, so that smaller defects can be detected, the working distance can be greater than 10 mm, on the basis of realizing the large-NA design, the system length is compressed, the number of original components is reduced, only five lenses are needed, the structure is simple, and installation and detection are facilitated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical technology, in particular to a deep ultraviolet spherical catadioptric inspection objective. BACKGROUND

[0002] In the semiconductor industry, the manufacture of chips or integrated circuits requires multiple photolithography and inspection, and the detection and screening of defects are crucial for improving the yield of semiconductor devices.

[0003] In the detection of chips or integrated circuits, the detection system is required not to contact the fragile wafer, and high-speed and high-resolution scanning is required to improve the detection efficiency and accuracy, so a detection objective with large numerical aperture, long working distance and high resolution is needed. In order to pursue extremely high resolution, traditional high-NA objective lenses usually adopt immersion or extremely high curvature lens design, which results in very short working distance and correction of various aberrations under certain NA, especially when pursuing higher resolution, traditional design often needs a large number of lenses. The complex structure makes the objective lens bulky and heavy, which is not convenient for integration into detection equipment. SUMMARY

[0004] The purpose of the present application is to provide a deep ultraviolet spherical catadioptric inspection objective to solve the problems raised in the background.

[0005] To achieve the above purpose, the present application provides the following technical scheme: a deep ultraviolet spherical catadioptric inspection objective, comprising:

[0006] A first lens group is provided on one side of the objective.

[0007] A second lens group is located between the first lens group and the objective, and the first lens group is used to converge light and correct the residual aberration of the second lens group.

[0008] An aperture stop is provided in the middle of the second lens group, and the second lens group and the aperture stop are used to correct the vertical axial aberration of the system.

[0009] Preferably, the first lens group comprises:

[0010] A first meniscus lens has positive focal power, and both sides of the first meniscus lens are provided with a first curved surface and a second curved surface, the first curved surface is concave, and the second curved surface is convex.

[0011] A second meniscus lens has positive focal power, and both sides of the second meniscus lens are provided with a third curved surface and a fourth curved surface, the third curved surface is concave, and the fourth curved surface is convex.

[0012] The double-convex lens has positive focal length, and fifth and sixth curved surfaces are arranged on both sides of the double-convex lens, and the fifth and sixth curved surfaces are convex.

[0013] Preferably, the second lens group comprises:

[0014] The third lens has positive focal length, and seventh and eighth curved surfaces are arranged on both sides of the third lens, the main body of the seventh curved surface is a plane, a concave spherical surface is arranged at the center of the seventh curved surface, the eighth curved surface is a concave surface.

[0015] The fourth lens has positive focal length, and ninth and tenth curved surfaces are arranged on both sides of the fourth lens, the ninth curved surface is a concave surface, and the tenth curved surface is a convex surface.

[0016] Preferably, the eighth curved surface of the third lens is coated with a mirror film for reflecting divergent light, and the plane of the seventh curved surface of the third lens is coated with an anti-reflection film for projecting light.

[0017] Preferably, the ratio of the diameter of the reflecting surface of the seventh curved surface of the third lens to the overall aperture of the lens is less than 0.1, the tenth curved surface of the fourth lens is coated with a mirror film, the center is coated with an anti-reflection film, and the ratio of the overall aperture to the light aperture is less than 0.1.

[0018] Preferably, the first meniscus lens, the second meniscus lens, the double-convex lens, the third lens and the fourth lens are made of the same fused quartz glass material.

[0019] Preferably, the third lens and the fourth lens are used for catadioptric light, and the catadioptric light beam can expand the numerical aperture of the system after passing through the third lens and the fourth lens.

[0020] Preferably, the optical structure composed of the first meniscus lens, the second meniscus lens, the double-convex lens, the third lens, the diaphragm and the fourth lens is suitable for a deep ultraviolet single-waveband light source, the wavelength can be any waveband in 193nm-365nm, and the bandwidth supports a narrow line width laser light source of ±0.06nm.

[0021] Preferably, the detection objective lens is an infinite imaging microscope objective lens, and can be used in cooperation with different focal length tubes, and the working distance of the detection objective lens is greater than 10mm.

[0022] Preferably, the maximum detection objective lens surface can reach 120μm, and the numerical aperture of the detection objective lens can be any value in 0.55-0.8.

[0023] Technical effects and advantages of the present application:

[0024] The objective lens of the present application adopts a spherical catadioptric structure, can realize deep ultraviolet waveband application, has a large numerical aperture, the numerical aperture can reach 0.8, a shorter wavelength and a larger numerical aperture have higher resolution, so that smaller defects can be detected, and the working distance can be greater than 10 mm, and on the basis of realizing the large NA design, the system length is compressed, the number of original elements is reduced, only 5 lenses are needed, the structure is simple, and installation and detection are convenient.

[0025] The working distance of the objective lens of the present application can reach 10 mm, a long working distance is realized on the basis of a large NA, and the objective lens is more suitable for non-contact detection, the catadioptric structure is adopted, and the system obscuration ratio is very small, and the obscuration ratio is less than 0.1. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is one of the schematic diagrams of the overall structure of the objective lens of the present application.

[0027] Figure 2 It is the second schematic diagram of the overall structure of the objective lens of the present application.

[0028] Figure 3 It is the modulation transfer function (MTF) curve of the objective lens of the present application.

[0029] Figure 4 It is the wavefront phase difference diagram of different fields of view of the objective lens of the present application.

[0030] In the figure: 1, first lens group; 11, first meniscus lens; 111, first curved surface; 112, second curved surface; 12, second meniscus lens; 121, third curved surface; 122, fourth curved surface; 13, double convex lens; 131, fifth curved surface; 132, sixth curved surface; 2, second lens group; 21, third lens; 211, seventh curved surface; 212, eighth curved surface; 22, fourth lens; 221, ninth curved surface; 222, tenth curved surface; 3, diaphragm. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] The present application provides an objective lens as Figures 1-4The deep ultraviolet spherical catadioptric detection objective lens shown comprises a first lens group 1, a second lens group 2 and a diaphragm 3, one side of the first lens group 1 is provided as an object plane, the first lens group 1 is located between the second lens group 2 and the object plane, the first lens group 1 is used for converging light rays and correcting residual aberrations of the second lens group 2, the diaphragm 3 is arranged in the middle of the second lens group 2, and the second lens group 2 and the diaphragm 3 are used for correcting coma and other axial aberrations of the system, the first lens group 1 is mainly responsible for the preliminary convergence of light beams and undertakes the main aberration correction task, thereby reducing the burden of the rear group, the diaphragm 3 is located in the middle of the second lens group 2, accurately controls the light beam aperture, cooperates with the catadioptric mirror, efficiently corrects coma, astigmatism and other axial aberrations, and ensures the imaging consistency in the field of view range, and the clear division of labor of the first lens group 1, the second lens group 2 and the diaphragm 3 makes the aberration correction more efficient, so that better results can be achieved with fewer lenses.

[0033] Specifically, the first lens group 1 comprises a first meniscus lens 11, a second meniscus lens 12 and a double convex lens 13, the first meniscus lens 11 has positive focal power, both sides of the first meniscus lens 11 are provided with a first curved surface 111 and a second curved surface 112, the first curved surface 111 is a concave surface, the second curved surface 112 is a convex surface, the first curved surface 111 faces the object side, can very efficiently receive large-angle incident light rays from the object plane without generating too much aberration, the meniscus structure itself has the characteristic of generating negative spherical aberration, is used for offsetting the positive spherical aberration generated by other positive lenses in the system, and is the main force for correcting spherical aberration, the second meniscus lens 12 has positive focal power, both sides of the second meniscus lens 12 are provided with a third curved surface 121 and a fourth curved surface 122, the third curved surface 121 is a concave surface, and the fourth curved surface 122 is a convex surface, the second meniscus lens 12 cooperates with the first meniscus lens 11, further converges light rays and continues to correct spherical aberration and field curvature, and the air gap between the two forms a “negative lens” effect, which is helpful to the control of astigmatism and other aberrations, the double convex lens 13 has positive focal power, both sides of the double convex lens 13 are provided with a fifth curved surface 131 and a sixth curved surface 132, the fifth curved surface 131 and the sixth curved surface 132 are both convex surfaces, and the double convex lens 13 is placed at the end of the front group, provides strong positive focal power, strongly converges light rays that have been corrected by the previous two lenses, and sends the light rays to the second lens group 2, the first meniscus lens 11 and the second meniscus lens 12 with positive focal power have concave surfaces facing the object side, can effectively converge large-angle light rays, and at the same time contribute negative spherical aberration, which is used for balancing the common positive spherical aberration in the system. The subsequent double convex lens 13 provides strong positive focal power and further converges light rays, the combination of the three lenses can efficiently correct spherical aberration, field curvature and astigmatism through precise curvature, thickness and spacing cooperation, lays a good foundation for the light rays entering the second lens group 2, and is a key front part for realizing high imaging quality.

[0034] Specifically, the second lens group 2 includes a third lens 21 and a fourth lens 22, both sides of the third lens 21 are provided with a seventh curved surface 211 and an eighth curved surface 212, the seventh curved surface 211 is a plane, the eighth curved surface 212 is a concave surface, the center of the seventh curved surface 211 is provided with a concave spherical surface, the concave spherical surface at the center of the seventh curved surface 211 can be used as a local phase corrector for fine optimization of the light path of a specific area, further suppressing residual high-order aberrations, which is a key detail to achieve the diffraction limit performance, the third lens 21 has positive focal power, the eighth curved surface 212 of the third lens 21 is coated with a mirror film for reflecting divergent light, the plane of the seventh curved surface 211 of the third lens 21 is coated with an anti-reflection film for projecting light, the eighth curved surface 212 is coated with a high-reflectivity film to become a concave mirror, light first enters from the seventh curved surface 211, passes through the lens material, is reflected after reaching the eighth curved surface 212, and then exits from the seventh curved surface 211 after passing through the same lens material again. The mirror itself does not introduce any chromatic aberration, but the two times of light passing through the refractive process of the lens provides an additional degree of freedom, which can use the curvature of the refractive surface to correct the spherical aberration inherent in the mirror itself. Both sides of the fourth lens 22 are provided with a ninth curved surface 221 and a tenth curved surface 222, the ninth curved surface 221 is a concave surface, and the tenth curved surface 222 is a convex surface. The diaphragm 3 is arranged between the third lens 21 and the fourth lens 22 for correcting astigmatism and other axial aberrations of the system. The fourth lens 22 has positive focal power and cooperates with the third lens 21 to form a symmetrical catadioptric structure to fold and converge light together. The diaphragm 3 is arranged between the two lenses to strictly limit the aperture and angle of the imaging beam, which is the core of successfully suppressing coma, astigmatism and other axial aberrations. The catadioptric structure is the physical basis for achieving high NA under long working distance. Through the catadioptric structure, the effective propagation distance of light is greatly increased in a limited physical space, so that an extremely curved refractive lens is not needed to collect light. This makes the front end of the objective lens flatter, thus easily achieving a working distance of more than 10 mm, while pushing the NA to 0.8.

[0035] Further, the diameter ratio of the reflecting surface of the seventh curved surface 211 of the third lens 21 to the overall aperture of the lens is less than 0.1, the tenth curved surface 222 of the fourth lens 22 is coated with a reflective film and the center is coated with an anti-reflection film, and the ratio of the clear aperture to the overall aperture is less than 0.1. The extremely small obscuration ratio reduces the negative impact on imaging contrast and resolution, so that the system has the advantages of catadioptric systems while avoiding most of their disadvantages. The final MTF curve of the imaging can still approach the diffraction limit system without obscuration, ensuring that the detection system can clearly distinguish low-contrast micro-defects.

[0036] Further, the first meniscus lens 11, the second meniscus lens 12, the lenticular lens 13, the third lens 21 and the fourth lens 22 are made of the same fused quartz glass material, and the materials of all the lenses are completely the same, which means that the refractive index (n) and the Abbe number (Vd, i.e. the dispersion coefficient) are completely consistent. When the dispersion characteristics of all the elements are the same, the inherent chromatic aberration of the system is fundamentally and completely eliminated. This is the simplest, most stable and most reliable achromatic solution for the detection system in a very narrow waveband (±0.06 nm). Fused quartz has very high transmittance (>99% / cm) and excellent anti-radiation damage capability in the deep ultraviolet waveband of 193 nm to 365 nm, and is the gold standard of optical materials in this waveband. In addition, the thermal expansion coefficient of fused quartz is extremely low, and it is not sensitive to environmental temperature changes. The thermal performance of all the lenses of the objective lens is consistent, which avoids defocus and image quality drift caused by temperature fluctuations, and ensures the stability and repeatability of the detection equipment in long-time high-speed operation.

[0037] Further, the third lens 21 and the fourth lens 22 are used for folding and reflecting light rays. The folding and reflecting of light rays by the third lens 21 and the fourth lens 22 can expand the numerical aperture of the system. The folding and reflecting structure acts as a “light ray angle amplifier”. Through the folding effect of the reflector, the light ray angle emitted from the object side is effectively amplified in the system, which is the direct reason for physically realizing high NA.

[0038] The optical structure composed of the first meniscus lens 11, the second meniscus lens 12, the lenticular lens 13, the third lens 21, the diaphragm 3 and the fourth lens 22 is suitable for a deep ultraviolet single waveband light source. The wavelength can be any waveband in the range of 193 nm to 365 nm. The system supports a narrow linewidth laser light source with a bandwidth of ±0.06 nm. The design covers the mainstream semiconductor lithography and detection wavelengths from KrF excimer laser (248 nm) to ArF excimer laser (193 nm), and supports a narrow linewidth laser light source with a bandwidth of ±0.06 nm. According to the Rayleigh criterion (Resolution=k*λ / NA), shorter wavelengths (such as 193 nm to 365 nm) directly bring higher theoretical resolution. This makes the objective lens capable of detecting smaller defects, meeting the detection needs from micrometer level to advanced 5 nm and 3 nm processes. One set of design can adapt to multiple light sources, enhancing the versatility and return on investment of the equipment.

[0039] The detection objective is an infinite imaging microscope objective, which can be used with different focal length tube lenses. The image side working distance of the detection objective is infinite, the object side working distance is greater than 10 mm, and the objective outputs parallel light, which allows filters, light splitting prisms, differential interference contrast (DIC) components, fluorescence modules, etc. to be inserted between the objective and the tube lens, greatly expanding the functionality and application scenarios of the detection system (such as multi-mode defect analysis). At the same time, the parallel light path is not sensitive to the change in the distance between the objective and the tube lens, reducing the difficulty of adjustment and improving the stability of the system. The object side working distance of more than 10 mm allows the use of faster and higher acceleration motion platforms for high-speed scanning, significantly improving the detection throughput. At the same time, the long working distance also provides space for integrating other sensors (such as confocal sensors).

[0040] The maximum object surface of the detection objective can reach 120 μm. Compared to the field of view of many high-NA objectives which is only two or three tens of microns, the field of view of 120 μm means that a larger area can be covered in a single exposure. Combined with a high-speed platform, the time required for full-scan can be significantly reduced, directly improving the detection efficiency and reducing the detection cost of a single chip. The numerical aperture of the detection objective can be any value between 0.55 and 0.8, providing flexibility in performance. When extremely high resolution defects need to be detected, a high NA (0.8) can be used. When the surface to be detected has a large fluctuation or needs to be scanned faster, a lower NA (such as 0.55) can be selected to obtain a larger depth of field and a more relaxed focusing tolerance.

[0041] Table 1 gives the specific parameters of the deep ultraviolet spherical catadioptric detection objective. The radius value R is positive, indicating that the center of curvature is close to the image side. The radius value R is negative, indicating that the center of curvature is close to the object side. The units of the radius, thickness, and aperture are millimeters.

[0042] Table 1 Specific parameters of deep ultraviolet spherical catadioptric detection objective

[0043]

[0044] Finally, it should be noted that the above description is only a preferred embodiment of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features, as long as they are within the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the scope of the present application should be included in the protection scope of the present application.

Claims

1. A deep ultraviolet catadioptric test objective, characterized in that The application relates to a lens system, which comprises: a first lens group (1), one side of which is arranged as an object plane, and which comprises: a first meniscus lens (11) with positive focal power, both sides of which are provided with a first curved surface (111) and a second curved surface (112), the first curved surface (111) being a concave surface, and the second curved surface (112) being a convex surface; a second meniscus lens (12) with positive focal power, both sides of which are provided with a third curved surface (121) and a fourth curved surface (122), the third curved surface (121) being a concave surface, and the fourth curved surface (122) being a convex surface; a double convex lens (13) with positive focal power, both sides of which are provided with a fifth curved surface (131) and a sixth curved surface (132), both the fifth curved surface (131) and the sixth curved surface (132) being convex surfaces; a second lens group (2), which is located between the first lens group (1) and the object plane, and is used for converging light rays and correcting residual aberration of the second lens group (2), and which comprises: a third lens (21), both sides of which are provided with a seventh curved surface (211) and an eighth curved surface (212), the main body of the seventh curved surface (211) being a plane, the center of the seventh curved surface (211) being provided with a concave spherical surface, the eighth curved surface (212) being a concave surface, the third lens (21) having positive focal power, the eighth curved surface (212) of the third lens (21) being coated with a reflecting film for reflecting divergent light rays, and the plane of the seventh curved surface (211) of the third lens (21) being coated with an anti-reflection film for transmitting light rays; a fourth lens (22), both sides of which are provided with a ninth curved surface (221) and a tenth curved surface (222), the ninth curved surface (221) being a concave surface, and the tenth curved surface (222) being a convex surface, the fourth lens (22) having positive focal power, the tenth curved surface (222) of the fourth lens (22) being coated with a reflecting film, and the center of the tenth curved surface (222) being coated with an anti-reflection film; a diaphragm (3), which is arranged between the third lens (21) and the fourth lens (22), and is used for correcting the astigmatism and other axial aberrations of the system.

2. The DUV catadioptric test objective of claim 1, wherein The ratio of the reflecting surface diameter of the seventh curved surface (211) of the third lens (21) to the overall aperture of the lens is less than 0.1, and the ratio of the light transmission aperture of the anti-reflection film coated on the center of the tenth curved surface (222) to the overall aperture is less than 0.

1.

3. The DUV catadioptric test objective of claim 1, wherein The first meniscus lens (11), the second meniscus lens (12), the double convex lens (13), the third lens (21) and the fourth lens (22) are all made of the same fused quartz glass material.

4. The DUV catadioptric test objective of claim 3, wherein The third lens (21) and the fourth lens (22) are used for folding and reflecting light rays, and the folded and reflected divergent light beams passing through the third lens (21) and the fourth lens (22) can expand the numerical aperture of the system.

5. The DUV catadioptric test objective of claim 1, wherein, The optical structure composed of the first meniscus lens (11), the second meniscus lens (12), the lenticular lens (13), the third lens (21), the diaphragm (3) and the fourth lens (22) is suitable for a deep ultraviolet single-band light source, and the wavelength can be any band in 193nm-365nm, and the bandwidth supports a narrow line width laser light source of ±0.06nm.

6. The DUV catadioptric test objective of claim 1, wherein, The detection objective lens is an infinite imaging microscopic objective lens, and can be used in cooperation with different focal length tubes.

7. The DUV catadioptric test objective of claim 1, wherein, The maximum detection objective lens object plane can reach 120μm, and the numerical aperture of the detection objective lens can be any value in 0.55-0.8.

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