Imaging system

Abstract

The present invention relates to the technical field of microscope imaging, and particularly discloses an imaging system applicable to broadband ultraviolet wavelength band imaging. 【Solution means】It includes a catadioptric lens group, a lens barrel lens group, and an optical path folding reflection assembly. The catadioptric lens group includes a catadioptric assembly, a field lens assembly, and a focus assembly. The catadioptric assembly focuses the light from the object on the field lens assembly to correct chromatic aberration. The light with corrected chromatic aberration is imaged on the image plane through the focus assembly, the lens barrel lens group, and the optical path folding reflection assembly in sequence. The magnification of the imaging system is M, and M = F1 / F2 is satisfied, where F1 is the focal length of the catadioptric lens group and F2 is the focal length of the lens barrel lens group. Moreover, the lens barrel lens group has a zoom range without changing the higher-order chromatic aberration, and the optical path folding reflection assembly has an optical path distance change range adapted to the zoom range of the lens barrel lens group.

Description

Technical Field

[0001] The present invention relates to the technical field of microscope imaging, and particularly to an imaging system particularly suitable for imaging in a broadband ultraviolet wavelength band.

Background Art

[0002] Ultraviolet detection microscopes have great application value in various fields such as physics, chemistry, materials science, and life science. Particularly in the fields of semiconductor industry and optoelectronic industry, deep ultraviolet detection microscopes are very important detection devices. They can be used for detection after exposure, development, etching, etc. of photolithography patterns on silicon wafers (or photomasks), and can quickly observe the overall effect of photolithography patterns on silicon wafers (or reticles), and can be used for measurement of the line width (CD) of photolithography patterns and defect detection, etc.

[0003] Since there are few materials available for chromatic aberration correction in the ultraviolet wavelength band, it is difficult to design a high-performance microscope suitable for the application of the broadband ultraviolet wavelength band. Also, in a wide zoom, it is even more difficult to correct the chromatic aberration of ultraviolet broadband optics.

[0004] Therefore, there is a need to provide a new imaging system suitable for imaging in the broadband ultraviolet wavelength band.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above problems, an object of the present invention is to provide an imaging system particularly applicable to imaging in the broadband ultraviolet wavelength band.

Means for Solving the Problems

[0006] To solve the above technical problems, an embodiment of the present invention provides an imaging system applicable to broadband ultraviolet wavelength band imaging, including a catadioptric lens group, a lens barrel lens group, and an optical path folding reflection assembly. The catadioptric lens group includes a catadioptric assembly, a field lens assembly, and a focus assembly. The catadioptric assembly focuses light from an object onto the field lens assembly to correct chromatic aberration. The light with corrected chromatic aberration is sequentially imaged on an image plane through the focus assembly, the lens barrel lens group, and the optical path folding reflection assembly. Here, the magnification of the imaging system is M, and it satisfies the conditional formula M = F1 / F2, where F1 is the focal length of the catadioptric lens group, F2 is the focal length of the lens barrel lens group, and the lens barrel lens group has a zoom range without changing the higher-order chromatic aberration. The optical path folding reflection assembly has an optical path distance change range adapted to the zoom range of the lens barrel lens group.

[0007] Preferably, the imaging system is applicable to imaging of light with a wavelength range of 250 - 450 nm.

[0008] Preferably, the distortion of the imaging system is less than 0.1%.

[0009] Preferably, the Strehl definition of the imaging system is greater than 0.9.

[0010] Preferably, the magnification of the imaging system is 50 - 250.

[0011] Preferably, the change in magnification within the wavelength range of the imaging system is less than 0.1%.

[0012] Preferably, the imaging system has an extremely high telecentricity of less than 1 mrad.

[0013] Preferably, the catadioptric assembly includes a first lens having a first reflective coating layer on its image side surface and a second lens having a second reflective coating layer on its object side surface. The second lens has a window for receiving light from an object, and the first lens has an opening at its center. The light received through the window is refracted by the second lens and the first lens in sequence onto the first reflective coating layer and then reflected by the first reflective coating layer. The light reflected by the first reflective coating layer is refracted by the first lens and the second lens in sequence onto the second reflective coating layer and then reflected by the second reflective coating layer. The light reflected by the first reflective coating layer is refracted by the second lens and then focused onto the field lens assembly.

[0014] Preferably, at least a part of the field lens assembly is located within the opening.

[0015] Preferably, the field lens assembly includes a plurality of lenses formed of refractive materials having at least two different dispersions, and the plurality of lenses are arranged in sequence from the object side to the image side.

[0016] Preferably, the refractive materials with different dispersions include fused silica and calcium fluoride.

[0017] Preferably, the plurality of lenses are divided into a third lens made of calcium fluoride, and a fourth lens and a fifth lens made of fused silica.

[0018] Preferably, the third lens is adhesively fixed to the object side of the fourth lens, the fifth lens is provided on the image side of the fourth lens and is spaced apart from the fourth lens, and the adhesive surface between the third lens and the fourth lens has the same radius of curvature.

[0019] Preferably, the fifth lens is adhered to the object side of the third lens, and the fourth lens is adhered to the image side of the third lens. Here, the adhesion surface between the third lens and the fourth lens has the same radius of curvature, and the adhesion surface between the fifth lens and the third lens has the same radius of curvature.

Advantages of the Invention

[0020] The beneficial effects of the present invention are as follows. By designing the structure of the imaging system, it can be particularly applied to imaging in the broad-band ultraviolet wavelength band.

Brief Description of the Drawings

[0021] To more clearly explain the technical solution of the embodiment of the present invention, the drawings necessary for the embodiment are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, based on these drawings without creative labor, other drawings can be obtained.

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0022] In order to make the object, solution means, and merits of the present invention clearer, each embodiment of the present invention will be described in detail below with reference to the drawings. However, it can be understood by those skilled in the art that many technical details are described in order to better understand the present invention in each embodiment of the present invention. However, the technical solution to be protected by the present invention can be realized even without these technical details and various changes and modifications based on the following embodiments.

[0023] The imaging system of the present invention is particularly suitable for ultraviolet imaging applications such as, for example, an ultraviolet microscope objective lens, a collector of surface scattered ultraviolet light in a wafer inspection device, and a mask projection optical system of an ultraviolet photolithography system.

[0024] Referring to FIG. 1, the imaging system according to the present invention includes a catadioptric lens group 1, a tube lens group 3, and an optical path folding reflection assembly 5. Light from an object is imaged on an image plane 9 through the catadioptric lens group 1, the tube lens group 3, and the optical path folding reflection assembly 5 in sequence.

[0025] Note that in FIG. 1, the direction of the arrow indicates the direction in which light travels from the object side to the image side.

[0026] As shown in FIG. 1, a reflecting element 8 having a reflecting surface is provided between the catadioptric lens group 1 and the tube lens group 3, and between the optical path folding reflection assembly 5 and the image plane 9. Here, the light emitted from the catadioptric lens group 1 is reflected by the reflecting surface of the reflecting element 8 to the tube lens group 3, and the light emitted from the optical path folding reflection assembly 5 is reflected by the reflecting surface of another reflecting element 8 to the image plane 9 for imaging.

[0027] As the reflecting element 8, a prism (for example, the triangular prism shown in FIG. 1), a plane mirror, or the like can be used.

[0028] Referring to FIG. 2, the catadioptric lens group 1 includes a catadioptric assembly 11, a field lens assembly 13, and a focus assembly 15. The catadioptric assembly 11 focuses the light from the object onto the field lens assembly 13 to correct chromatic aberration. The light with corrected chromatic aberration is sequentially imaged on the image plane 9 through the focus assembly 15, the lens barrel lens group 3, and the optical path folding reflection assembly 5. Here, the magnification of the imaging system is M, and M = F1 / F2 is satisfied, where F1 is the focal length of the catadioptric lens group 1, F2 is the focal length of the lens barrel lens group 3, and the lens barrel lens group 3 has a zoom range without changing the higher-order chromatic aberration. The optical path folding reflection assembly 5 has an optical path distance change range adapted to the zoom range of the lens barrel lens group 3.

[0029] In a specific embodiment, the catadioptric lens group 1 has a focal length of 23.35 mm and an optical length of 345 mm.

[0030] The catadioptric assembly 11 includes a first lens 111 having a first reflection coating layer 112 on its image side surface and a second lens 113 having a second reflection coating layer 114 on its object side surface. The second lens 113 has a window 115 for receiving light from the object, and the first lens 111 has an opening 117 at its center. The light received by the window 115 is refracted by the second lens 113 and the first lens 111 in sequence onto the first reflection coating layer 112 and reflected by the first reflection coating layer 112. The light reflected by the first reflection coating layer 112 is refracted by the first lens 111 and the second lens 113 in sequence onto the second reflection coating layer 114 and reflected by the second reflection coating layer 114. The light reflected by the first reflection coating layer 112 is refracted by the second lens 113 and then focused on the field lens assembly 13.

[0031] It should be noted that the optical aperture of the window 115 does not necessarily have to be limited by the opening 117 and may be simply limited by the second reflection coating layer 114. Specifically, the window 115 is formed by exposing the area where the second reflection coating layer 114 is not applied on the object side surface of the transparent lens.

[0032] Note that the first reflective coating layer 112 and the second reflective coating layer 114 may be a magnesium fluoride coating layer or an aluminum coating layer. Optionally, the first reflective coating layer 112 and the second reflective coating layer 114 may be polarization protected to increase the reflectivity.

[0033] In a specific embodiment, the diameter of the window 115 is 1 mm, the diameter of the aperture 117 is 48 mm, and the exit angle range is ±21 mrad.

[0034] At least a part of the field lens assembly 13 is located within the aperture 117. This can sufficiently reduce the aperture of the aperture 117, which is advantageous for focusing more light on the field lens assembly 13.

[0035] The field lens assembly 13 includes a plurality of lenses formed of refractive materials having at least two different dispersions, and the plurality of lenses are arranged in order from the object side to the image side.

[0036] In this embodiment, the refractive materials with different dispersions include fused quartz and calcium fluoride.

[0037] As shown in FIGS. 2 and 3, the plurality of lenses are divided into a third lens 131 made of calcium fluoride, a fourth lens 133 made of fused quartz, and a fifth lens 135.

[0038] As shown in FIG. 2, the third lens 131 is adhesively fixed to the object side 133 of the fourth lens, the fifth lens 135 is provided on the image side of the fourth lens 133 and is spaced from the fourth lens 133, and the adhesive surface between the third lens 131 and the fourth lens 133 has the same radius of curvature.

[0039] The third lens 131 has a flat object side and a convex image side. The fourth lens 133 has a concave object side and a convex image side. The fifth lens 135 has a convex object side and a concave image side. Note that both the object side and the image side of the fifth lens 135 are weakly curved surfaces.

[0040] Referring to FIG. 3, the fifth lens 135 is adhered to the object side of the third lens 131, and the fourth lens 133 is adhered to the image side of the third lens 131. Here, the adhesion surface between the third lens 131 and the fourth lens 133 has the same radius of curvature, and the adhesion surface between the fifth lens 135 and the third lens 131 has the same radius of curvature.

[0041] The fifth lens 135 has both a flat object side and a flat image side. The third lens 131 has a flat object side and a convex image side. The fourth lens 133 has a concave object side and a convex image side.

[0042] Note that the field lens assembly 13 shown in FIG. 3 is more suitable for wavefront correction than the field lens assembly 13 shown in FIG. 2.

[0043] As shown in FIGS. 2 and 3, the focus assembly 15 includes a plurality of lenses from the object side to the image side. The plurality of lenses are an a-lens 151, a b-lens 152, a c-lens 153, a d-lens 154, an e-lens 155, an f-lens 156, and a g-lens 157, respectively. Here, the a-lens 151 has a concave object side and a concave image side, the b-lens 152 has a flat object side and a convex image side, the c-lens 153 has a convex object side and a convex image side, the d-lens 154 has a convex object side and a concave image side, the e-lens 155 has a concave object side and a convex image side, the f-lens 156 has a convex object side and a flat image side, and the g-lens 157 has a concave object side and a concave image side.

[0044] The lens barrel lens group 3 has a plurality of lenses from the object side toward the image side, and the overall focal length of the lens barrel lens group 3 can be adjusted by adjusting the distance between the lenses.

[0045] In addition, in order for the lens barrel lens group 3 to be zoomable without changing the higher-order chromatic aberration, the focal length may be adjusted by adjusting the distance between at least two lenses, or the focal length may be adjusted by replacing the entire lens barrel lens group 3 having different distances between at least two lenses.

[0046] As shown in FIG. 4, the plurality of lenses are an A lens 31, a B lens 33, a C lens 35, and a D lens 37, respectively. Here, the object side surface of the A lens 31 is convex, and its image side surface is concave. The object side surface of the B lens 33 is flat, and its image side surface is convex. The object side surface of the C lens 35 is concave, and its image side surface is flat. The object side surface of the D lens 37 is concave, and its image side surface is convex.

[0047] As shown in FIG. 1, the optical path folding reflection assembly 5 includes a plurality of light reflection elements. The plurality of light reflection elements are an A light reflection element 51, a B light reflection element 53, a C light reflection element 55, a D light reflection element 57, an E light reflection element 58, and an F light reflection element 59, respectively. Here, the A light reflection element 51 and the B light reflection element 53 constitute the first set of light reflection elements. The C light reflection element 55, the D light reflection element 57, the E light reflection element 58, and the F light reflection element 59 constitute the second set of light reflection elements. The first set of light reflection elements and the second light reflection elements can move away from or face each other to realize a change in the optical path distance.

[0048] As the light reflection element, a prism (for example, the triangular prism shown in FIG. 1), a plane mirror, etc. can be used.

[0049] The imaging system is applied to the imaging of light with a wavelength range of 250 to 450 nm. Note that the autofocus wavelength of the imaging system is 470 nm.

[0050] The imaging system has a distortion of less than 0.1%.

[0051] The imaging system has a Strehl ratio greater than 0.9. In general, for the imaging system, the Strehl ratio at lower wavelengths is lower, except for the automatic wavelength, because the diffraction limit is lower at lower wavelengths.

[0052] The magnification of the imaging system is from 50 to 250. For example, when the focal length of the lens barrel lens group 3 is 1168 mm, the magnification of the imaging system is 50 times; when the focal length of the lens barrel lens group 3 is 5838 mm, the magnification of the imaging system is 250 times.

[0053] The change in magnification within the wavelength range of the imaging system is less than 0.1%.

[0054] The extremely high telecentricity of the imaging system is less than 1 mrad.

[0055] As will be understood by those skilled in the art, the above embodiments are specific embodiments for implementing the present invention, and in actual applications, various changes can be made to the form and details without departing from the gist and scope of the present invention.

Claims

1. An imaging system applicable to broadband ultraviolet wavelength band imaging, comprising a catadioptric lens group, a lens barrel lens group, and an optical path folding reflection assembly, The catadioptric lens group includes a catadioptric assembly, a field lens assembly, and a focus assembly. The catadioptric assembly focuses light from an object onto the field lens assembly to correct chromatic aberration. The light with corrected chromatic aberration is sequentially imaged on an image plane through the focus assembly, the lens barrel lens group, and the optical path folding reflection assembly. The magnification of the imaging system is M, and it satisfies the conditional formula M = F1 / F2, where F1 is the focal length of the catadioptric lens group, F2 is the focal length of the lens barrel lens group, and the lens barrel lens group has a zoom range without changing higher-order chromatic aberration. The optical path folding reflection assembly has an optical path distance change range adapted to the zoom range of the lens barrel lens group. An imaging system characterized by this.

2. The imaging system according to claim 1, characterized in that it is applicable to imaging of light with a wavelength range of 250 to 450 nm.

3. The imaging system according to claim 1, characterized in that the distortion aberration is less than 0.1%.

4. The imaging system according to claim 1, characterized in that the Strehl ratio is greater than 0.

9.

5. The imaging system according to claim 1, characterized in that the magnification is 50 to 250.

6. The imaging system according to claim 5, characterized in that the change in magnification within the wavelength range is less than 0.1%.

7. The imaging system according to claim 1, characterized in that the extremely high telecentricity is less than 1 mrad.

8. The catadioptric assembly includes a first lens having a first reflective coating layer on its image side surface and a second lens having a second reflective coating layer on its object side surface. The second lens has a window for receiving light from an object, and the first lens has an opening at its center. The light received through the window is refracted by the second lens and the first lens in sequence and then reflected by the first reflective coating layer. The light reflected by the first reflective coating layer is refracted by the first lens and the second lens in sequence and then reflected by the second reflective coating layer. The light reflected by the first reflective coating layer is refracted by the second lens and then focused on the field lens assembly. The imaging system according to claim 1, characterized in that

9. The imaging system according to claim 8, characterized in that at least a part of the field lens assembly is located within the opening.

10. The imaging system according to claim 1, characterized in that the field lens assembly includes a plurality of lenses formed of refractive materials having at least two different dispersions, and the plurality of lenses are arranged in sequence from the object side to the image side.

11. The imaging system according to claim 10, characterized in that the refractive materials with different dispersions include fused quartz and calcium fluoride.

12. The imaging system according to claim 11, characterized in that the plurality of lenses are divided into a third lens made of calcium fluoride, a fourth lens and a fifth lens made of fused quartz.

13. The imaging system according to claim 12, characterized in that the third lens is adhesively fixed to the object side of the fourth lens, the fifth lens is provided on the image side of the fourth lens and is spaced apart from the fourth lens, and the adhesive surface between the third lens and the fourth lens has the same radius of curvature.

14. The imaging system according to claim 12, characterized in that the fifth lens is adhesively bonded to the object side of the third lens, the fourth lens is adhesively bonded to the image side of the third lens, the adhesive surface between the third lens and the fourth lens has the same radius of curvature, and the adhesive surface between the fifth lens and the third lens has the same radius of curvature.

Images