CN113126283B

CN113126283B - Wide spectral line and large visual field optical system

Info

Publication number: CN113126283B
Application number: CN201911392646.8A
Authority: CN
Inventors: 刘鹏
Original assignee: Zhangjiagang Zhonghe Automation Technology Co ltd
Current assignee: Zhangjiagang Zhonghe Automation Technology Co ltd
Priority date: 2019-12-30
Filing date: 2019-12-30
Publication date: 2022-09-30
Anticipated expiration: 2039-12-30
Also published as: CN113126283A

Abstract

The invention provides a wide-spectral-line large-field-of-view optical system, which comprises: a light source unit, an illumination unit, an imaging unit; the lighting unit receives a light beam from the light source unit, and includes: first illumination camera lens, dodging part, second illumination camera lens, the light beam that comes from the light source unit passes through first illumination camera lens, dodging part, second illumination camera lens in proper order and throws on an object plane, and imaging unit accepts the light beam that comes from the object plane, and it includes: the imaging lens is arranged in sequence, any imaging lens corresponds to an image plane, and light beams from the lighting unit are sequentially imaged by the first imaging lens and the at least one second imaging lens and then are amplified step by step. The wide-spectrum large-field optical system is suitable for being used in the deep ultraviolet wavelength range of 200nm to 450nm, and has the effects of improving the magnification, shortening the length of the whole system and saving the space by arranging the first imaging lens and the at least one second imaging lens.

Description

Wide spectral line and large visual field optical system

Technical Field

The invention relates to the technical field of optics, in particular to a wide-spectrum large-view-field optical system.

Background

In the semiconductor field of LDSI (large scale integrated circuit), the difficulty of microfabrication is the greatest in which photolithography is the core. In the development and manufacturing process of LDSI, it is necessary to perform a plurality of high-precision optical detections on high-precision fine line patterns made of various different characteristic materials, and there is a demand for high stability and high-speed detection in the manufacturing field. Because the information content of various optical detection is very large, optical detection systems with ultra-large visual field, high resolution and wide spectral lines including ultraviolet wave bands are in use, and the demand is increasing.

As the integration density of semiconductor chips and devices increases, optical inspection systems are required to have higher optical resolution. The main factors determining the optical resolution are the wavelength of light and the numerical aperture, so in order to improve the resolution of the optical detection system, the wavelength range of the illumination light source of the optical system is increasingly shortened, such as near ultraviolet light and even deep ultraviolet light; the numerical aperture of the detection objective lens is increasingly increased and approaches the limit. In the ultraviolet wavelength region, especially in the deep ultraviolet wavelength region of 200nm to 450nm, the absorption of general optical materials is very large, the light transmittance is very low, and applicable optical materials are very limited, so that the design and manufacture of optical systems of wide spectral lines including the ultraviolet band, large field of view, and high resolution become very difficult. Since the solutions to the above problems are very limited, practical solutions are urgently needed.

Disclosure of Invention

The invention aims to provide an optical system with wide spectral line and large visual field, which overcomes the defects in the prior art.

In order to solve the technical problems, the technical scheme of the invention is as follows:

a wide-line, large-field-of-view optical system, comprising: a light source unit, an illumination unit, an imaging unit;

the illumination unit receives a light beam from the light source unit, and includes: the device comprises a first illumination lens, a light homogenizing component and a second illumination lens;

the light beam from the light source unit is projected on an object plane through the first illumination lens, the dodging component and the second illumination lens in sequence, the imaging unit receives the light beam from the object plane, and the imaging unit comprises: the imaging lenses are sequentially arranged, any imaging lens corresponds to an image plane, and after the light beam from the illumination unit is projected on the object plane, the reflected and scattered light beam is sequentially imaged by the first imaging lens and the at least one second imaging lens and then is amplified step by step;

the first imaging lens comprises the following components in sequence: the imaging lens group comprises a first imaging lens group, a second imaging lens group and a third imaging lens group;

an optical path separation element is also arranged between the illumination unit and the first imaging lens;

the light beams from the illumination unit sequentially pass through the light path separation element, the second imaging lens group and the first imaging lens group to reach the object plane, and the light beams reflected and scattered from the object plane sequentially pass through the first imaging lens group, the second imaging lens group, the light path separation element and the third imaging lens group to form a first image plane;

the first imaging lens group and the second imaging lens group satisfy the relation: f1/f2 is more than 0.35 and less than 1.5, and the second imaging mirror group and the third imaging mirror group satisfy the relation: f3/(f2 x beta) < 0.22 < 0.8;

wherein f2 is the combined focal length of the second imaging lens group, f3 is the combined focal length of the third imaging lens group, and β is the magnification ratio of the first imaging lens group;

different pupil filters are selectively inserted at the aperture stop of the illuminating unit and the aperture stop of the second imaging lens;

and field diaphragms are arranged at the second illumination surface and the first imaging surface of the illumination unit, and the clear aperture of each field diaphragm is arranged corresponding to the size of the FOV (field of view) of the object space.

As an improvement of the wide-spectrum large-field optical system, any one of the illuminating lenses comprises the following components in sequence: first illumination mirror group illumination aperture diaphragm and second illumination mirror group, in the first lighting lens, the preceding focus of first illumination mirror group is located first illumination face department, the entry setting of dodging part is in the back focus department of second illumination mirror group, the light beam warp that the light source sent becomes parallel light or nearly parallel light behind the first illumination mirror group, passes through illumination aperture diaphragm with assemble the back focus behind the second illumination mirror group, get into the entry of dodging part.

As an improvement of the wide-spectrum-line large-field-of-view optical system, in the first illuminating lens, the second illuminating lens group can move back and forth along the direction of the optical axis, the light homogenizing component comprises at least two components capable of being switched with each other, the at least two light homogenizing components have different geometric sizes, adaptive illuminating conditions can be obtained when the FOVs of object fields of the corresponding optical systems are different, the position of an outlet is kept unchanged during switching of the light homogenizing component, the second illuminating lens group moves back and forth along the optical axis, and the back focus of the second illuminating lens group and the inlet of the light homogenizing component are kept at the same position, so that light beams emitted by the second illuminating lens group can enter the light homogenizing component most effectively.

As an improvement of the wide-spectrum large-field optical system of the present invention, the first imaging lens group includes, directed from the object plane side to the image plane side: the lens comprises a first compound lens, a second lens and a third reflector; the object plane side curved surface of the first compound lens comprises a reflecting surface, the central part of the object plane side curved surface of the first compound lens is a transmitting surface, and the peripheral part of the object plane side curved surface of the first compound lens is a reflecting surface facing to the image side; the object plane side curved surface of the third reflector is a concave reflecting surface, and the center of the third reflector is provided with a through hole which can allow light beams to pass through.

As an improvement of the wide-spectrum large-field optical system, light beams from the object plane form an intermediate image after passing through the first imaging mirror group, and the intermediate image is formed near a central through hole of the third reflector; the first imaging lens group satisfies the relation: i f 1/R2I is less than 0.35, I f 1/R3I is less than 0.8; wherein f1 is the combined focal length of the first imaging lens group, R2 is the radius of curvature of the image plane side curved surface of the first compound lens at the object plane side, and R3 is the radius of curvature of the object plane side curved surface of the second lens at the object plane side.

As an improvement of the wide-spectrum large-field optical system of the present invention, the intermediate image satisfies the relation: and the I Ti/f2 is less than 0.4, and Ti is the distance between the intermediate image and the first lens in the object space of the second imaging lens group.

As an improvement of the wide-spectrum large-field optical system of the present invention, the second imaging lens group is a lens group adapted to form parallel light or near-parallel light; at least 2 positive lenses in the second imaging lens group satisfy the relation: dop >0.7 XD 1, and the 2 positive lenses with the shortest focal length satisfy the relation: 0.7 < (1/fp1+1/fp2) × f2 < 1.9;

at least 2 negative lenses satisfy the relation: dop >0.7 XD 1, and the 2-piece negative lens in which the absolute value of the focal length is the shortest satisfies the relation: 0.45 < |1/fm1+1/fm2| × f2 < 1.4;

wherein, Dop is the clear aperture of the lens, D1 is the diameter of the aperture diaphragms of the second lens group (G2) and the third lens group (G3), fp1 is the focal length of the shortest positive lens with the focal length satisfying the relational expression Dop >0.7 × D1, fp2 is the focal length of the second shortest positive lens with the focal length satisfying the relational expression Dop >0.7 × D1, fm1 is the focal length of the shortest negative lens with the absolute value satisfying the relational expression Dop >0.7 × D1, fm1 is the focal length of the second shortest negative lens with the absolute value satisfying the relational expression Dop >0.7 × D1.

As an improvement of the wide-spectrum large-field optical system, the second imaging lens comprises a fourth imaging lens group, an aperture diaphragm and a fifth imaging lens group; the fourth imaging lens group comprises a sub lens group with first positive focal power, a sub lens group with negative focal power and a sub lens group with second positive focal power, and the relation is satisfied:

0.3＜f111/f11＜1.6；

0.13＜-f112/f11＜0.8；

0.2＜f113/f11＜1.1；

wherein f11 is the combined focal length of the fourth imaging lens group, f111 is the combined focal length of the first positive focal power sub-lens group, f112 is the combined focal length of the negative focal power sub-lens group, and f113 is the combined focal length of the second positive focal power sub-lens group;

the lens surface of the sub-lens group with negative focal power, which is closest to the object side, in the fourth imaging lens group is a convex surface facing the object side, the lens surface of the sub-lens group with negative focal power, which is closest to the image side, is a concave surface facing the image side, the lens surface of the sub-lens group with second positive focal power, which is closest to the object side, is a convex surface facing the object side, and the lens surface of the sub-lens group with second positive focal power, which is closest to the image side, is a convex surface facing the image side.

As an improvement of the wide-spectrum large-field optical system, the fifth imaging lens group comprises at least two groups which can be replaced with each other, any one group has a corresponding different imaging magnification, the at least two groups of mutually switched fifth imaging lens groups correspond to the same imaging position, and an image sensor is arranged at the same imaging position; when the different fifth imaging lens group is switched, the image sensor keeps the position still, and light beams emitted by object field of view FOVs with different sizes are received at different imaging magnifications.

As an improvement of the wide-spectrum large-field optical system, the aberration coefficient of the wide-spectrum large-field optical system is NA ² ×FOV×λmax/(λmin) ² >2；

Wherein NA is the object-side numerical aperture; FOV is object field, unit: millimeter; λ max is the longest wavelength of the spectrum for which the objective lens is suitable, in units: micron size; λ min is the shortest wavelength of the spectrum suitable for the objective lens, unit: and (3) micron.

Compared with the prior art, the invention has the beneficial effects that: the wide-spectrum large-field optical system is suitable for being used in the deep ultraviolet wavelength range of 200nm to 450nm, and has the effects of improving the magnification, shortening the length of the whole system and saving the space by arranging the first imaging lens and the at least one second imaging lens.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a schematic diagram of a wide-spectral-line large-field-of-view optical system according to an embodiment of the present invention;

FIG. 2 is a schematic view of a first imaging lens group according to an embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a wide-spectral-line large-field-of-view optical system for cooperatively illustrating optical parameters of a first imaging lens;

FIG. 4 is a schematic structural diagram of a second imaging lens according to an embodiment of the disclosure;

FIG. 5 is a schematic view of the fourth imaging lens group shown in FIG. 4;

fig. 6 is a graph of MTF of the transfer function of the first imaging lens.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1, the wide-spectral-line large-field optical system of the present embodiment includes: a light source unit 1, an illumination unit 2, and an imaging unit 3.

The light beam emitted by the light source unit 1 is projected on an object plane through the illumination unit 2 in sequence and is imaged with large resolution after passing through the imaging unit 3. In one embodiment, the light source unit 1 includes: a light source 11 and a light-gathering element 12 for gathering the light beam emitted by the light source 11. In the present embodiment, the light condensing element 12 has an arc-shaped mirror surface structure, and the light source 11 is located at the focal point of the arc-shaped mirror surface. In this way, the light converging element 12 converges the light flux emitted from the light source 11 on the illumination surface S1, and forms a spatial image of the light source 11.

The illumination unit 2 receives the light beam from the light source unit 1 and projects it into the imaging unit 3. The lighting unit 2 comprises the following components arranged in sequence: a first illumination lens 21, a dodging component RD and a second illumination lens 23. Therefore, the light beam from the light source unit 1 is projected onto an object plane through the first illumination lens 21, the dodging unit RD and the second illumination lens 23 in sequence to illuminate the object plane.

The first illumination lens 21 and the second illumination lens 23 have the same structure, wherein the first illumination lens 21 includes, in sequence: a first illumination lens group G21, an illumination aperture stop AS2 and a second illumination lens group G22. The first illumination lens 22 includes, in order: a first illumination lens group G31, an illumination aperture stop AS3 and a second illumination lens group G32.

Meanwhile, in the first illumination lens 21, the front focus of the first illumination lens group G21 is located at the first illumination surface S1, the entrance of the dodging member RD is located at the rear focus of the second illumination lens group G32, and the light beam emitted by the light source 11 passes through the first illumination lens group G21 and becomes parallel light, and then passes through the second illumination lens group G32 and converges to the rear focus, and enters the entrance of the dodging member RD. The first lighting lens group G21 moves back and forth along the optical axis along with the entrance of the dodging unit RD, and the back focus of the first lighting lens group G21 and the entrance of the dodging unit RD are kept at the same position.

In the second illumination lens group, the AS3 at the illumination aperture stop can be inserted into a pupil filter, and the pupil filter can change the spatial distribution of a pupil function, so that the corresponding diffraction spot distribution is changed, and super resolution is realized. Wherein the pupil filter includes an amplitude type pupil filter and a phase type pupil filter.

In one embodiment, the dodging part RD may be a prism rod or a fly-eye lens, the prism rod is a cylinder with a rectangular, square, regular hexagon, regular triangle, etc. cross section, and the edge line of the cylinder is perpendicular to the end surface. By arranging the dodging unit RD, the space image of the light source 11 can be regularly divided into a plurality of parts and then superposed together, and finally, an illumination surface with uniform light intensity is obtained.

Further, the light uniformizing part RD may adopt two sets which can be replaced with each other. The two groups of light homogenizing parts RD correspond to different illumination ranges respectively, but the outlets of the light homogenizing parts RD keep the same position. This has the advantage that the light source 11 is kept free from movement, making the construction simple.

In order to achieve the effects of shortening the length of the whole system and saving space, a reflector is further disposed between the illumination unit 2 and the imaging unit 3, and the reflector can change the exit angle of the light beam exiting from the illumination unit 2 and introduce the light beam into the imaging unit 3.

The imaging unit 3 receives a light beam from an object plane, and realizes high-magnification imaging with a large field of view. Specifically, the imaging unit 3 includes: a first imaging lens 31 and at least one second imaging lens 32, so that imaging with corresponding magnification is realized by arranging at least one second imaging lens 32. For example, when one second imaging lens 32 is provided, 2-stage magnification can be realized. The

imaging lenses

31 and 32 are sequentially arranged, any one of the

imaging lenses

31 and 32 corresponds to an image plane, and after the light beam from the illumination unit 2 is projected on the object plane, the reflected and scattered light beam is sequentially imaged by the first imaging lens 31 and the at least one second imaging lens 32 and then is amplified step by step.

The first imaging lens 31 includes, in order: the first imaging lens group G1, the second imaging lens group G2 and the third imaging lens group G3.

Wherein the first imaging lens group G1 includes, from the object plane side to the image plane side: the lens comprises a first compound lens, a second lens and a third reflector.

The object side curved surface of the first compound lens forms one reflecting surface M2, the object side curved surface of the third lens forms the other reflecting surface M1, the third reflector is provided with a through hole at the center for allowing the light beam to pass through, the central part of the object side curved surface of the first compound lens is a transmission surface, and the peripheral part of the object side curved surface of the first compound lens is a reflecting surface facing the image side. Therefore, the optical components with small quantity are adopted, the structure is simplified, and the effect of correcting various optical aberrations is achieved by effectively utilizing the optical components to the maximum extent.

As shown in fig. 2, the first imaging lens group satisfies the relation: i f 1/R2I is less than 0.35, I f 1/R3I is less than 0.8; wherein f1 is the combined focal length of the first imaging lens group, R2 is the radius of curvature of the image plane side curved surface of the object plane side first compound lens, and R3 is the radius of curvature of the object plane side curved surface of the object plane side second compound lens. If the above-described limits are exceeded, correction of high-order chromatic aberration and spherical aberration may be difficult.

The first imaging lens group G1 includes at least two reflecting surfaces and at least one refractive lens, and the middle area of the at least two reflecting surfaces is an area suitable for light beam transmission. The light beams from the object plane form an intermediate image after passing through the first imaging lens group G1, and the intermediate image is formed near the central through hole of the third reflector.

The intermediate image satisfies the relation: and the I Ti/f 2I is less than 0.4, and Ti is the distance between the intermediate image and the first lens of the second imaging lens group in the object space. Beyond the upper limit of the above relation, aberration correction may be difficult, especially primary and high-order aberration correction may be difficult, resulting in a complicated lens structure and an increase in manufacturing cost.

The second group of imaging lenses G2 is a lens group adapted to form parallel light or near-parallel light.

In the second imaging lens group, at least 2 positive lenses satisfy the relation: dop >0.7 XD 1, and the 2 positive lenses with the shortest focal length satisfy the relation: 0.7 < (1/fp1+1/fp2) × f2 < 1.9;

wherein, Dop is the clear aperture of the lens, D1 is the diameter of the aperture stop of the second lens group (G2) and the third lens group (G3), fp1 is the focal length of the shortest positive lens satisfying the relation Dop >0.7 × D1 focal length, fp2 is the focal length of the second shortest positive lens satisfying the relation Dop >0.7 × D1 focal length, fm1 is the focal length of the shortest absolute value negative lens satisfying the relation Dop >0.7 × D1 focal length, and fm1 is the focal length of the second shortest absolute value negative lens satisfying the relation Dop >0.7 × D1 focal length.

By providing the second imaging lens group satisfying the above-mentioned relational expression, it is possible to achieve an effect of correcting various aberrations in a balanced manner without generating excessive high-order aberrations.

wherein f2 is the combined focal length of the second imaging lens group, f3 is the combined focal length of the third imaging lens group, and β is the magnification of the first imaging lens group. When the limit of the relational expression between the first imaging lens group and the second imaging lens group is exceeded, it may be difficult to correct chromatic aberration and field curvature aberration in particular; beyond the lower limit, spherical aberration correction in particular can be difficult. Further, when the limit of the relational expression between the second imaging lens group and the third imaging lens group is exceeded, it may be difficult to cause correction of high-order chromatic aberration and spherical aberration; it can also be difficult to direct the coaxial epi-illumination beam from the structure.

The third imaging lens group G3 includes: at least two positive lenses and at least one negative lens.

Therefore, the light emitted from the object plane passes through the first set of imaging lenses G1 to form an intermediate image, which is located near the reflective surface of the second set of imaging lenses G2. The intermediate image forms approximately parallel light after passing through the second imaging lens group G2 or the approximately parallel light passes through the third imaging lens group G3 and then is imaged on an image surface S3 at a finite distance.

Further, a mirror group G4 and an optical path separating element BS are provided between the illumination unit 2 and the first imaging lens 31. The light beam from the illumination unit 2 sequentially passes through the lens group G4, the optical path separating element BS, the second imaging lens group G2 and the first imaging lens group G1 to reach the object plane, and the light beam from the object plane sequentially passes through the first imaging lens group G1, the second imaging lens group G2, the optical path separating element BS and the third imaging lens group G3 to form the image plane S3.

Accordingly, the light converging element 12 converges the light beam emitted from the light source 11 to the illumination surface S1, forms a spatial image of the light source 11, and then uniformly projects to the second illumination surface S2. The light beam emitted from the light source 11 is introduced into the first imaging lens 31 through the lens group G4 and the optical path splitting element BS, and is projected onto the object plane, so as to illuminate the object plane.

With reference to fig. 3, the optical parameters of the first imaging lens 31 are shown in table 1 below:

parameter values of the objective lens:

NA＝0.9；

object space field diameter: 1.2 mm;

wavelength: 260-450 nm.

NA is the numerical aperture of the object.

TABLE 1

Wherein the surface 1 is aspheric and is expressed by the following formula

c＝1/R1＝0

k＝0

α1＝-0.002282233

α2＝0.001063988

α3＝-0.000641664

α4＝0.00020374

α5＝-2.62E-05

The characteristic parameters are shown in table 2.

TABLE 2

The calculated values of the relationships are shown in table 3:

(1)	f3/(f2×β)	0.50
			(2)	f1/f2	0.80
(3)	\|f1/R2\|	0.20
			(4)	\|f1/R3\|	0.46
(5)	(1/fp1+1/fp2)×f2	1.16
			(6)	\|1/fm1+1/fm2\|×f2	0.77
(7)	\|Ti/f2\|＜0.4	0.07
			(8)	NA2×FOV×λmax/(λmin)2	6.47

TABLE 3

As shown in fig. 4 and 5, the second imaging lens 32 is used to achieve re-imaging of the image plane S3 on the image plane S4, and includes, in sequence: a fourth imaging lens group G11, an aperture diaphragm AS1 and a fifth imaging lens group G12; the fourth imaging lens group G11 includes a sub-lens group G111 with a first positive power, a sub-lens group G112 with a negative power, and a sub-lens group G113 with a second positive power, and satisfies the relation:

0.3＜f111/f11＜1.6；

0.13＜-f112/f11＜0.8；

0.2＜f113/f11＜1.1。

wherein f11 is the combined focal length of the fourth imaging lens group, f111 is the combined focal length of the first positive power sub-lens group G111, f112 is the combined focal length of the negative power sub-lens group G112, and f113 is the combined focal length of the second positive power sub-lens group G113.

The lens surface of the sub-lens group G112 with negative power closest to the object in the fourth imaging lens group is a convex surface facing the object, the lens surface of the sub-lens group G112 with negative power closest to the image is a concave surface facing the image, the lens surface of the sub-lens group G113 with second positive power closest to the object is a convex surface facing the object, and the lens surface of the sub-lens group G113 with second positive power closest to the image is a convex surface facing the image.

The optical parameters of the first imaging lens 32 are shown in table 4 below:

TABLE 4

For example, the characteristic parameters are shown in table 5.

TABLE 5

For example, the calculated values of the relationships are shown in table 6:

(1)	f111/f11	0.75
			(2)	-f112/F11	0.35
(3)	f113/f11	0.44

TABLE 6

The fifth imaging lens group G12 adopts two groups which can be replaced with each other. The two second imaging lens groups G2 have different imaging magnifications but the same imaging position image plane S4. This has the advantage that the image sensor position at the image plane 2 is kept free from moving, making the structure simple. Different pupil filters may be inserted at the imaging aperture stop AS 1.

Defining the aberration coefficient of wide-spectrum large-field optical system as NA ² ×FOV×λmax/(λmin) ² >2. Wherein NA is the object-side numerical aperture; FOV is object field of view, unit: millimeter; λ max is the longest wavelength of the spectrum available for the objective lens, in units: micron size; λ min is the shortest wavelength of the spectrum applicable to the objective lens, unit: and (3) micron.

This patent introduces the concept of aberration coefficients to compare and evaluate the technical difficulty and complexity of optical lens systems.

The aberration coefficient can represent the technical difficulty of the optical system of the embodiment, and the aberration coefficient comprises the comprehensive influence of factors of the field size FOV, the resolution and the applicable wavelength range of the optical system. The larger the aberration coefficient is, the larger the field of view is, the higher the resolution is, the wider the spectral band is, these factors all directly increase the technical difficulty of the optical system, including many aspects such as design, applicable material, manufacturing, assembling and debugging, and detection operation, the difficulty and cost of the light source and image sensor adapted thereto, and other associated devices are also correspondingly increased.

The aberration coefficient of the conventional optical system is mostly 0.3-1, while the aberration coefficient of the optical system of the present embodiment is larger than 2, which can reach 6.47. The comprehensive technical difficulty of the optical system is several times higher than that of the existing optical system.

In addition, in the optical system of the embodiment, all the lens and mirror elements do not include aspheric surfaces, so that the difficulty and cost of processing, detection and installation and correction can be greatly reduced. Meanwhile, all the lenses are made of quartz or calcium fluoride crystal materials. In the ultraviolet wavelength region, especially the deep ultraviolet wavelength region of 200nm to 450nm, the absorption of the common optical material is very large, the light transmittance is very low, and the light transmittance of the optical system can be improved by using quartz glass or calcium fluoride crystals. Both materials are suitable for use, and correcting the various optical aberrations of the system can become difficult, especially as numerical apertures increase.

As shown in fig. 6, the MTF is a graph of the transfer function of the first imaging lens 31. Wherein, the horizontal axis is resolution, the unit is line pair/millimeter (lp/mm), and the line pair number capable of being resolved per millimeter is the value of the resolution. The vertical axis represents the modulation Transfer function (mtf), which is a quantitative description of the resolution of the lens. The contrast is expressed by Modulation (Modulation). Assuming that the maximum luminance is Imax, the minimum luminance is Imin, and the modulation degree M is defined as: m ═ i (Imax-Imin)/(Imax + Imin). The modulation is between 0 and 1, with a greater modulation indicating a greater contrast. When the maximum brightness and the minimum brightness are completely equal, the contrast disappears completely, and the modulation degree is equal to 0.

For a sine wave with an original modulation degree of M, if the modulation degree of an image reaching an image plane through a lens is M', the MTF function value is as follows: MTF value is M'/M.

It can be seen that the MTF value must be between 0 and 1, and the closer to 1, the better the performance of the lens. If the MTF value of the lens is equal to 1, the modulation degree of the lens output completely reflects the contrast of the input sine wave; whereas if the modulation degree of the input sine wave is 1, the modulation degree of the output image is exactly equal to the MTF value. The MTF function therefore represents the contrast of the lens at a certain spatial frequency.

Further, as can be seen from the curves in fig. 4, the MTF values for the representative 0 field, 0.5 field and maximum field are already very close to the diffraction limit values. The diffraction limit means that when an ideal object point is imaged by an optical system, due to the limitation of diffraction of light of physical optics, an ideal image point cannot be obtained, but a fraunhofer diffraction image is obtained, and the diffraction image is the diffraction limit, namely the maximum value, of the physical optics.

It can be seen that the invention can approach the diffraction limit of physical optics over a wide spectrum range of 260-450 nm over the entire field of view. The analysis result shows that the wave aberration WFE (RMS) of the whole field is less than 0.05 wavelength in the spectrum range of 260-450 nm.

In summary, the wide-spectrum large-field optical system of the present invention is suitable for use in the deep ultraviolet wavelength range of 200nm to 450nm, and has the effects of increasing the magnification, shortening the length of the whole system, and saving space by providing the first imaging lens and the at least one second imaging lens.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. A wide-spectrum large-field optical system, adapted for use in the ultraviolet range, comprising: a light source unit, an illumination unit, an imaging unit;

light beams from the illumination unit sequentially pass through the light path separation element, the second imaging lens group and the first imaging lens group to reach the object plane, light rays emitted by the object plane form an intermediate image after passing through the first imaging lens group, and the intermediate image forms parallel light or approximately parallel light after passing through the second imaging lens group and then is imaged to an image plane at a finite distance through the third imaging lens group;

different pupil filters are selectively inserted at the aperture stop of the illumination unit and the aperture stop of the second imaging lens;

and field diaphragms are arranged at the second illumination surface and the first imaging surface of the illumination unit, and the clear aperture of each field diaphragm is arranged corresponding to the size of the FOV of the object space field.

2. The wide-spectrum large-field optical system according to claim 1, wherein any one of the illumination lenses comprises, in sequence: first illumination mirror group, illumination aperture diaphragm and second illumination mirror group, in the first lighting lens, the preceding focus of first illumination mirror group is located first illumination face department, the entry setting of dodging part is in the back focus department of second illumination mirror group, the light beam warp that the light source sent becomes parallel light or nearly parallel light behind the first illumination mirror group, passes through illumination aperture diaphragm with assemble the back focus behind the second illumination mirror group, get into the entry of dodging part.

3. The wide-spectrum large-field optical system according to claim 2, wherein in the first illumination lens, the second illumination lens group can move back and forth along the optical axis, the dodging component includes at least two kinds that can be switched with each other, the at least two kinds of dodging components have different geometric dimensions, when the FOV of the object field of the optical system is different, adaptive illumination conditions can be obtained, the position of the exit is kept unchanged during switching of the dodging component, the second illumination lens group moves back and forth along the optical axis, the back focus of the second illumination lens group and the entrance of the dodging component are kept at the same position, and therefore the light beam emitted by the second illumination lens group can enter the dodging component most effectively.

4. The wide-line large-field optical system of claim 1, wherein said first set of imaging mirrors comprises, pointing from the object plane side to the image plane side: the lens comprises a first compound lens, a second lens and a third reflector; the object plane side curved surface of the first compound lens comprises a reflecting surface, the central part of the object plane side curved surface of the first compound lens is a transmitting surface, and the peripheral part of the object plane side curved surface of the first compound lens is a reflecting surface facing to the image side; the object plane side curved surface of the third reflector is a concave reflecting surface, and the center of the third reflector is provided with a through hole which can allow light beams to pass through.

5. The wide-spectrum large-field optical system according to claim 4, wherein the light beam from the object plane passes through the first imaging lens group to form an intermediate image, and the intermediate image is formed near the central through hole of the third reflector; the first imaging lens group satisfies the relation: i f 1/R2I is less than 0.35, I f 1/R3I is less than 0.8; wherein f1 is the combined focal length of the first imaging lens group, R2 is the radius of curvature of the image plane side curved surface of the object plane side first compound lens, and R3 is the radius of curvature of the object plane side curved surface of the object plane side second compound lens.

6. The wide-line large-field optical system of claim 5, wherein the intermediate image satisfies the relation: and the I Ti/f 2I is less than 0.4, and Ti is the distance between the intermediate image and the first lens of the second imaging lens group in the object space.

7. The wide-line large-field optical system of claim 1, wherein said second set of imaging mirrors is a set of mirrors adapted to form parallel light or near-parallel light; in the second imaging lens group, at least 2 positive lenses satisfy the relation: dop >0.7 XD 1, and the 2 positive lenses with the shortest focal length satisfy the relation: 0.7 < (1/fp1+1/fp2) × f2 < 1.9;

at least 2 negative lenses satisfy the relation: dop >0.7 × D1, and the 2 negative lenses in which the absolute value of the focal length is the shortest satisfy the relation: 0.45 < |1/fm1+1/fm2| × f2 < 1.4;

8. The wide-line large-field optical system of claim 1, wherein the second imaging lens comprises a fourth imaging lens group, an aperture stop and a fifth imaging lens group; the fourth imaging lens group comprises a sub lens group with first positive focal power, a sub lens group with negative focal power and a sub lens group with second positive focal power, and the relation is satisfied:

0.3＜f111/f11＜1.6；

0.13＜-f112/f11＜0.8；

0.2＜f113/f11＜1.1；

9. The wide-spectrum large-field optical system according to claim 8, wherein said fifth imaging lens group comprises at least two mutually replaceable groups, each group having a different imaging magnification, at least two mutually switchable groups of the fifth imaging lens group corresponding to a same imaging position, and an image sensor is disposed at the same imaging position; when the different fifth imaging lens group is switched, the image sensor keeps the position still, and light beams emitted by object field of view FOVs with different sizes are received at different imaging magnifications.

10. The wide-spectrum large-field optical system according to any one of claims 1 to 9, wherein an aberration coefficient of the wide-spectrum large-field optical system is NA ² ×FOV×λmax/(λmin) ² >2；

Wherein NA is the object-side numerical aperture; FOV is object field of view, unit: millimeter; λ max is the longest wavelength of the spectrum for which the objective lens is suitable, in units: micron size; λ min is the shortest wavelength of the spectrum suitable for the objective lens, unit: and (3) micron.