CN117369082A - Objective lens and optical system - Google Patents

Abstract

An objective lens and an optical system, the objective lens comprising a lens group for converging parallel light beams of different wavelengths at one focal point, and/or the lens group for parallel emission of light beams from the focal point of the lens group, the lens group comprising a mirror group having at least one first reflecting surface; at least one diffraction plane for scattering the light beam and reducing the dispersion of the objective lens. According to the invention, the first reflecting surface and the diffraction surface can realize the self correction of the aberration of the wide-spectrum objective lens, so that the performance of the objective lens is improved, the detection performance of an optical system is correspondingly improved, and the objective lens is also convenient to independently produce, assemble and detect.

Description

Objective lens and optical system

Technical Field

The embodiment of the invention relates to the technical field of optical detection, in particular to an objective lens and an optical system.

Background

The optical defect detection of the wafer mainly detects and identifies the defects of integrated circuits on the wafer, so as to detect whether defects such as grooves, particles, scratches and the like exist in the wafer or not and detect the positions of the defects.

The inspection apparatus requires a special optical inspection system to image defects, and a specially designed objective lens can realize inspection requirements of such an optical inspection apparatus, and the objective lens requires excellent optical properties such as high numerical aperture, large field of view and wide spectrum, thereby improving accuracy and efficiency of defect inspection.

However, the performance of the objective lens is still to be improved.

Disclosure of Invention

The embodiment of the invention solves the problem of providing an objective lens and an optical system, which are beneficial to improving the performance of the objective lens, thereby improving the detection performance of the optical system.

To solve the above problems, an embodiment of the present invention provides an objective lens, including: the lens group is used for converging parallel light beams with different wavelengths to one focus, and/or is used for enabling the light beams from the focus of the lens group to exit in parallel, and comprises a reflector group which is provided with at least one first reflecting surface; at least one diffraction plane for scattering the light beam and reducing the dispersion of the objective lens.

Correspondingly, the embodiment of the invention also provides an optical system comprising the objective lens provided by the embodiment of the invention.

Compared with the prior art, the technical scheme of the embodiment of the invention has the following advantages:

in the objective lens provided by the embodiment of the invention, the lens group comprises a reflector group, the reflector group is provided with at least one first reflecting surface, and the objective lens also comprises at least one diffraction surface, which is used for scattering the light beam and reducing the dispersion of the objective lens; the first reflection surface is used for reducing limitation on the optical wavelength, the light beam is reflected by the first reflection surface, so that a better correcting effect on chromatic aberration can be achieved, the objective lens can be compatible with a wider spectral wavelength range (for example, light with a spectral wavelength range of 260-500 nm is compatible), so that the objective lens can be suitable for more detection scenes, meanwhile, the objective lens is also provided with a diffraction surface, the diffraction surface scatters the light beam and reduces dispersion of the objective lens, and therefore the diffraction surface can achieve a better correcting effect on aberration (for example, chromatic aberration including a second-order spectrum and monochromatic aberration), and the correction of the aberration of the objective lens can be achieved under the condition that the lens group adopts a smaller number of optical elements; in summary, the embodiment of the invention can realize the self-correction of the aberration of the wide-spectrum objective lens by performing the above-mentioned arrangement on the objective lens, thereby improving the performance of the objective lens, being correspondingly beneficial to improving the detection performance of the optical system integrated with the objective lens, reducing the dependence on other optical compensation components (for example, being easy to enable the objective lens to adapt to other tube lenses with good aberration correction so as to achieve excellent imaging effect), being capable of realizing the correction of the aberration of the objective lens, and being further convenient for independently producing, assembling and detecting the objective lens.

Drawings

FIG. 1 is a schematic view of an objective lens and an optical path diagram according to an embodiment of the present invention;

FIG. 2 is a schematic view of a diffraction structure of one of the diffraction planes in an objective lens according to an embodiment of the present invention;

FIG. 3 is a schematic view showing a diffraction structure of another diffraction plane in the objective lens according to an embodiment of the present invention;

FIG. 4 is a graph of MTF for an objective lens at a 0mm field of view position in accordance with an embodiment of the present invention;

FIG. 5 is a graph of MTF for an objective lens of an embodiment of the present invention at a 0.35mm field of view position;

FIG. 6 is a graph of MTF for an objective lens of an embodiment of the present invention at a 0.5mm field of view position;

fig. 7 is a vertical chromatic aberration diagram of an objective lens according to an embodiment of the present invention.

Detailed Description

As known from the background art, the performance of the objective lens still needs to be improved.

It has been found that, since the objective lens includes a plurality of lenses, the performance of the objective lens is limited by the lens material, and it is difficult for the objective lens to completely correct the self-aberration, and a relay lens group or a variable magnification lens group is often required to compensate the aberration of the objective lens. However, this in turn brings about two problems: 1) The objective lens has obvious aberration, which is not beneficial to the assembly and detection of the objective lens; 2) The objective lens can only be used together with a custom optimized tube lens, and when other tube lenses with good self-aberration optimization are replaced, the aberration of the objective lens and the difference of the tube images cannot be compensated for each other, so that the imaging quality is seriously attenuated.

In order to solve the technical problem, an embodiment of the present invention provides an objective lens, including: the lens group is used for converging parallel light beams with different wavelengths to one focus, and/or is used for enabling the light beams from the focus of the lens group to exit in parallel, and comprises a reflector group which is provided with at least one first reflecting surface; at least one diffraction plane for scattering the light beam and reducing the dispersion of the objective lens.

According to the embodiment of the invention, by the arrangement of the objective lens, the aberration of the wide-spectrum objective lens can be self-corrected, so that the performance of the objective lens is improved, the detection performance of an optical system integrated with the objective lens is correspondingly improved, the dependence on other optical compensation components is reduced (for example, the objective lens is easy to adapt to other tube lenses with good aberration correction so as to achieve excellent imaging effects), the correction of the aberration of the objective lens can be realized, and the independent production, assembly and detection of the objective lens are also facilitated.

In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

Fig. 1 is a schematic structural view and an optical path diagram of an objective lens according to an embodiment of the present invention.

Referring to fig. 1, the objective lens 50 includes: a mirror group (not shown) for converging parallel light beams of different wavelengths at one focal point and/or for parallel emission of light beams from the focal point of the mirror group, the mirror group comprising a mirror group (not shown) having at least one first reflecting surface 52; at least one diffraction plane 51 for scattering the light beam and reducing the dispersion of the objective lens 50.

The light beams of different wavelengths have different spectral wavelength ranges, and therefore, imaging definition is improved by converging parallel light beams of different wavelengths at one focal point.

The lens group comprises a reflector group, the reflector group is provided with at least one first reflecting surface 52, the light beam passes through the first reflecting surface 52 to reduce the limitation of the spectrum wavelength, the light beam passes through the first reflecting surface 52 to realize reflection, so that the limitation of the spectrum wavelength can be reduced, a better correcting effect can be achieved on chromatic aberration, the objective lens 50 can be compatible with a wider spectrum wavelength range (for example, the light with the spectrum wavelength range of 260nm to 500nm is compatible), and the objective lens 50 can be suitable for more detection scenes.

In this embodiment, the optical element (e.g., a lens or a mirror) where the first reflecting surface 52 is located has a high reflecting film, and the high reflecting film is used to provide the first reflecting surface 52. As an example, the material of the high reflection film includes aluminum, and the preferable reflection characteristics of aluminum are utilized to improve the reflection performance of the first reflection surface 52.

The objective lens 50 further comprises at least one diffraction surface 51, and the diffraction surface 51 scatters the light beam and reduces the dispersion of the objective lens, so that the diffraction surface 51 can have a better correction effect on aberration (such as chromatic aberration including secondary spectrum and monochromatic aberration), which is beneficial to the correction of the aberration of the objective lens itself in the case that the objective lens 50 adopts a smaller number of optical elements.

Specifically, based on the dispersion characteristics of the diffraction surface 51, the diffraction surface 51 is used to scatter the light beam and reduce the dispersion of the objective lens, so that the diffraction surface 51 can have a better correction effect on the aberration, which is advantageous in that the correction of the aberration of the objective lens 50 itself is achieved in the case that the objective lens 50 employs a smaller number of optical elements, and the diffraction surface 51 can also have a better correction effect on the chromatic aberration, thereby combining the diffraction surface 51 and the first reflection surface 52 to further improve the correction effect on the chromatic aberration.

In summary, by providing the first reflecting surface 52 and the diffraction surface 51 in the objective lens 50, the aberration of the objective lens 50 with a wide spectrum can be self-corrected, so that the performance of the objective lens 50 is improved, the detection performance of the optical system integrated with the objective lens 50 is correspondingly improved, the dependence on other optical compensation components is reduced (for example, the objective lens 50 is easily adapted to other tube lenses with good aberration correction, so as to achieve an excellent imaging effect), the aberration of the objective lens 50 can be corrected, and the objective lens 50 is also conveniently produced, assembled and detected independently.

In this embodiment, the mirror group includes at least two first reflecting surfaces 52, and at least one first reflecting surface 52 is a curved reflecting surface 55.

In one embodiment, the mirror group is used to image the object plane to be measured, so that at least one first reflecting surface 52 is a curved reflecting surface 55, and the curved reflecting surface 55 is used to focus the parallel incident light beam to the focal point of the curved reflecting surface 55.

The light beam can be converged through the curved reflecting surface 55 by the curved reflecting surface 55.

In this embodiment, the at least two first reflecting surfaces 52 further have a turning mirror 80, where the turning mirror 80 is used to change the imaging position of the reflecting mirror group, so that the imaging position of the reflecting mirror group and the focal point of the curved reflecting surface 55 are located at two sides of the curved reflecting surface 55 respectively; the curved reflective surface 55 and the turning mirror 80 are disposed opposite to each other.

The beam is reflected a plurality of times by the turning mirror 80 via the first reflecting surface 52, and the imaging position of the mirror group is changed by the plurality of reflections, thereby enhancing the correction effect on chromatic aberration.

In this embodiment, the number of the first reflecting surfaces 52 is plural, the first reflecting surfaces 52 are located on different optical elements, and the curved reflecting surfaces 55 and the turning mirror 80 are disposed opposite to each other, which makes the distance between the first reflecting surfaces 52 adjustable, thereby being beneficial to improving the design freedom.

In this embodiment, the central area or the edge area of the two first reflecting surfaces 52 has a light passing area adapted to pass the light beam, and the central area is disposed at a position where the optical axis passes, so that the light beam from outside the mirror group can enter between the two first reflecting surfaces 52 via the light passing area and exit via the light passing area.

As an example, the reflective coating has an opening in the central region such that the central region is a light-passing region, thereby enabling a light beam to enter between the two first reflective surfaces 52 via the opening (i.e. via the light-passing region) and exit via the light-passing region.

In other embodiments, the first reflective surface has a central aperture in a central or edge region such that the light beam is transmitted through the central aperture.

Specifically, the central region is provided at a position where the optical axis passes, so that the light beam can pass through the central region.

As an example, the mirror group is used for imaging an object plane to be measured, so that a light beam from outside the mirror group is reflected to the turning mirror 80 by the curved reflecting surface 55, and the light beam is reflected by the turning mirror 80 and then exits by the light passing area of the curved reflecting surface 55.

In other embodiments, depending on the transmission direction of the light beam, it may also be: the light beams from the outside of the reflector group are reflected to the curved surface reflecting surface through the turning reflector, and the light beams are reflected by the curved surface reflecting surface and then emitted out through the light passing area of the turning reflector.

In this embodiment, the lens group includes one or more lenses (not shown) sequentially arranged in the optical axis direction; of the plurality of lenses, at least one of the lenses has a diffraction surface 51.

In this embodiment, the diffraction surface 51 and the first reflection surface 52 are different surfaces, which is advantageous in that the degree of freedom in design is improved (for example, it is easy to adjust the distance between the diffraction surface 51 and the first reflection surface 52).

In other embodiments, the diffractive surface may also be a second reflective surface, that is, the diffractive surface and the reflective surface are integrated on the same surface.

In this embodiment, the lens group further includes: the refractive lens 18 is located between the two first reflecting surfaces 52, and the optical path between the two first reflecting surfaces 52 passes through the refractive lens 18 a plurality of times, and the refractive lens 18 is used for increasing the numerical aperture of the objective lens 50.

By the refractive lens 18, the beam is reflected between the first reflecting surfaces 52 while the angle of the beam is made larger, thereby facilitating an increase in the Numerical Aperture (NA) and field of view of the objective lens 50. For example, the numerical aperture may be up to 0.9, which may provide excellent resolution limits, and the field of view (FOV) may be up to 1mm, which may provide a larger throughput for the detection system.

In summary, by providing the first reflecting surface 52 and the refractive lens 18 between the two first reflecting surfaces 52 in the objective lens 50, it is possible to obtain an objective lens 50 having a high numerical aperture, a large field of view, and a wide spectrum, and the chromatic aberration correction performance of the objective lens 50 is good.

In this embodiment, the distance between the refractive lens 18 and the first reflecting surface 52 is adjustable, so that the design freedom is improved.

As an example, the number of refractive lenses 18 between the two first reflective surfaces 52 is one. In other embodiments, the number of refractive lenses between the two first reflective surfaces may also be plural.

Therefore, the objective lens 50 of the present embodiment has the first reflecting surfaces 52 and the refractive lens 18 located between the first reflecting surfaces 52, and further has the diffraction surfaces 51, so that by the above arrangement of the objective lens 50, a catadioptric objective lens can be obtained, thereby obtaining a wide-spectrum objective lens, having a self-correcting function of aberration, having a larger Numerical Aperture (NA) and a larger field of view, further improving the performance of the objective lens, being beneficial to improving the detection performance of the optical system integrated with the objective lens 50, reducing the dependence on other optical compensation components (for example, being easy to adapt the objective lens to other tube lenses with good aberration correction, so as to achieve excellent imaging effect), being capable of realizing the correction of the aberration of the objective lens, and being convenient to separately produce, assemble and detect the objective lens.

The larger the number of diffraction surfaces 51, the higher the degree of freedom in modulating aberration and chromatic aberration and the better the modulation effect, but increasing the number of diffraction surfaces 51 correspondingly increases the manufacturing cost of the objective lens 50. For this reason, in the present embodiment, the number of the diffraction surfaces 51 is 2, considering the modulation of aberration and chromatic aberration, and the manufacturing cost.

As an example, the objective lens 50 includes two diffraction surfaces 51 disposed opposite to each other, thereby facilitating processing when the two diffraction surfaces 51 are disposed.

In other embodiments, the diffraction surfaces may be spaced apart by a portion of the lens surface.

In this embodiment, two opposite diffraction surfaces 51 are respectively located on adjacent lenses.

In this embodiment, the plane on which the diffraction surface 51 is located is a plane.

In order to obtain the diffraction surface 51, the lens surface needs to be processed to form a diffraction structure on the lens surface, so that the diffraction structure can be formed on a plane by making the surface of the diffraction surface 51 be a plane, thereby reducing processing difficulty, which is correspondingly beneficial to improving processing precision, and further improving the modulation precision of the diffraction surface 51 for aberration and chromatic aberration, and therefore, the effect of correcting chromatic aberration and chromatic aberration in the large-field microscope objective lens is remarkable by utilizing the dispersion characteristic and the aspherical characteristic of the diffraction surface 51.

In other embodiments, the surface on which the diffraction surface is located may be a surface having curvature, such as a spherical surface or an aspherical surface.

In this embodiment, the lens surface on which the diffraction surface 51 is located has a diffraction structure capable of producing a diffraction effect in the optical path, and is used to provide the diffraction surface 51.

Specifically, referring to fig. 2 and 3 in combination, fig. 2 is a schematic view of a diffraction structure of one of the diffraction surfaces 51 (i.e., the first diffraction surface 13) in the present embodiment, and fig. 3 is a schematic view of a diffraction structure of the other diffraction surface 51 (i.e., the second diffraction surface 14) in the present embodiment, where the diffraction structure is a plurality of concentric annular diffraction structures with a position corresponding to the optical axis as a center C, and the direction pointing from the center C to the edge of the lens, the intervals between adjacent annular diffraction structures decrease in order, and in the case that the diffraction surfaces 51 are a plurality, the diffraction surface far from the object has a larger diffraction structure density.

In this embodiment, the objective lens 50 includes a focusing lens group 61, a field lens group 62 and an imaging lens group 63 sequentially arranged along an optical axis direction, at least one of the focusing lens group 61, the field lens group 62 and the imaging lens group 63 includes the reflecting mirror, the focusing lens group 61 and the imaging lens group 63 are respectively located at two sides of an intermediate image plane along the optical axis direction, the imaging lens group 63 is closest to the object space, the field lens group 62 is located in a preset position area between the focusing lens group 61 and the imaging lens group 63, the imaging lens group 63 is used for imaging an object plane to form an intermediate image in the intermediate image plane, the field lens group 62 is suitable for performing chromatic aberration correction on a passing light beam, and the preset position area includes a position of the intermediate image plane; the focusing lens group 61 is used for enabling light beams from one point of the intermediate image plane to exit in parallel.

When the light beams are transmitted to the focusing lens group 61 by the imaging lens group 63, the focusing lens group 61 is used for collimating the light beams with the same transmission direction and converging the light beams for imaging through a tube lens in the optical system. Accordingly, when the light beam is transmitted from the focusing lens group 61 to the imaging lens group 63, the focusing lens group 61 is used for receiving the light beam and converging the light beam in the same transmission direction.

The focusing lens group 61 includes a plurality of lenses having the same material so that monochromatic aberration can be corrected, and after determining the material, the curvatures and positions of the respective lenses in the focusing lens group 61 are easily set so as to satisfy the correction effects of monochromatic aberration and chromatic aberration, and the focusing effect or the collimation effect on the light beam.

As an example, the material of the lenses in the focusing lens group 61 includes fused silica.

In this embodiment, the lens of the focusing lens group 61 has the diffraction surface 51.

The aperture of the lens of the focusing lens group 61 is larger, and a sufficient area is provided for processing the diffraction structure, so that the processing difficulty of the diffraction structure is reduced, the processing precision is improved correspondingly, and the modulation precision of the diffraction surface 51 to the aberration and the chromatic aberration is improved.

As an example, in the focusing lens group 61, one or more lenses farthest from the object side in the optical axis direction have the diffraction surface 51.

The field lens set 62 is located in a preset position area between the focusing lens set 61 and the imaging lens set 63, and the preset position area includes the position of the intermediate image plane, so that the field lens set 62 is arranged near the intermediate image, which is beneficial to better effect of correcting distortion and field curvature.

In this embodiment, the field lens set 62 includes a plurality of lenses having different materials. By increasing the kind of material of the field lens group 62, the chromatic aberration correction effect of the objective lens 50 is further provided.

As one example, the materials of the lenses in the field lens set 62 include fused silica and calcium fluoride.

The numerical aperture, field of view, and compatible spectral range of the objective lens 50 are thereby increased by the imaging lens group 63.

As an example, the focusing lens group 61 is configured to receive parallel light beams with different wavelengths and converge the parallel light beams with the same transmission direction to form an intermediate image, and therefore, the imaging lens group 63 is configured to re-image the light corrected by the field lens group 62, thereby imaging the light onto the final image surface 17.

In this embodiment, the imaging lens group 63 includes a plurality of lenses having the same material, so that after the material is determined, the curvature and the position of each lens in the imaging lens group 63 are easily set to satisfy the correction effect on chromatic aberration.

As one example, the material of the lenses in the imaging lens group 63 includes fused silica.

In a specific embodiment, from the image side to the object side, the focusing lens group 61 includes a first plano-convex positive lens 1, a plano-concave negative lens 2, a first meniscus negative lens 3, a first biconvex positive lens 4, a second biconvex positive lens 5, and a second meniscus negative lens 6, which are sequentially arranged along the optical axis direction, and the plane of the first plano-convex positive lens 1, the concave surface of the plano-concave negative lens 2, the convex surface of the first meniscus negative lens 3, and the convex surface of the second meniscus negative lens 6 are all oriented to the object side.

Correspondingly, the plane of the first plano-convex positive lens 1 facing the plano-concave negative lens 2 is a diffraction plane 51 (i.e., the first diffraction plane 13), and the plane of the plano-concave negative lens 2 facing the first plano-convex positive lens 1 is also a diffraction plane 51 (i.e., the second diffraction plane 14).

Taking the focusing lens group 61 for receiving the light beam and converging the incident light as an example, the light beam is continuously converged along with the increase of the propagation distance, the light beam is transmitted and diverged to a certain extent by the plano-concave negative lens 2 and the first meniscus negative lens 3, and then converged by the first biconvex positive lens 4, the second biconvex positive lens 5 and the first meniscus positive lens 6, so that the light beam can be propagated forward along the light path for a certain distance while converging, and further imaging is realized at the middle image plane position.

In the present embodiment, the field lens group includes a third biconvex positive lens 7, a fourth biconvex positive lens 8, a biconcave negative lens 9, and a fifth biconvex positive lens 10, which are sequentially arranged in the optical axis direction.

In this embodiment, from the image side to the object side, the imaging lens group 63 includes a meniscus mirror 15, a third meniscus negative lens 11, and a second plano-convex positive lens 12 sequentially arranged along the optical axis direction, the concave surface of the meniscus mirror 15, the concave surface of the third meniscus negative lens 11, and the plane of the plano-convex lens 12 are all oriented toward the object side, and the surface of the second meniscus negative lens 15 oriented toward the object side and the surface of the plane lens 12 oriented toward the object side are each provided with the first reflecting surface 52. Correspondingly, the second meniscus negative lens 15 is used for providing a curved reflecting surface, and the plane lens 12 is a turning mirror.

As shown in fig. 4, fig. 4 is a graph of MTF (modulation transfer function) of the objective lens 50 at a 0mm field position, where the abscissa represents spatial frequency and the ordinate represents contrast. The MTF is a method of measuring an optical frequency, and is measured in terms of how many lines can be present in a range of 1mm, and the unit is expressed in line/mm.

In fig. 4, a curve L1 represents an MTF curve corresponding to a diffraction limit (Diffraction limit), and a curve L2 represents an MTF curve corresponding to a line of the objective lens 50 at a 0mm field position, as can be seen from fig. 4, the MTF curve of the objective lens 50 at the 0mm field position in this embodiment is relatively close to the MTF curve of the diffraction limit.

As shown in fig. 5, fig. 5 is an MTF graph of the objective lens 50 at a 0.35mm field of view position, wherein the abscissa represents a spatial frequency, the ordinate represents a contrast, a curve L1 represents an MTF curve corresponding to a diffraction limit, a curve L3 represents an MTF curve of the objective lens 50 at a 0.35mm field of view position, along a meridian direction, and a curve L4 represents an MTF curve of the objective lens 50 at a 0.35mm field of view position, along a sagittal direction perpendicular to a field of view diameter direction. As can be seen from fig. 5, with the above arrangement, the MTF curve of the objective lens 50 at the 0.35mm field of view position in this embodiment is relatively close to the MTF curve of the diffraction limit.

As shown in fig. 6, fig. 6 is an MTF graph of the objective lens 50 at a 0.5mm field of view position, wherein the abscissa represents a spatial frequency, the ordinate represents a contrast, a curve L1 represents an MTF curve corresponding to a diffraction limit, a curve L5 represents an MTF curve of the objective lens 50 at a 0.5mm field of view position, along a meridian direction, and a curve L6 represents an MTF curve of the objective lens 50 at a 0.5mm field of view position, along a sagittal direction perpendicular to a field of view diameter direction. As can be seen from fig. 6, with the above arrangement, the MTF curve of the objective lens 50 at the 0.5mm field of view position in this embodiment is also closer to the MTF curve of the diffraction limit.

Referring to fig. 7 in combination, fig. 7 is a vertical chromatic aberration diagram of the objective lens 50 of the present embodiment, in which the abscissa represents the focal point deviation value (micrometers) of light of different wavelengths, the ordinate represents the distance from the center of the field of view in the field of view diameter direction, the straight line L7 represents light of 380nm in wavelength, the curve L8 represents light of 260nm in wavelength, the curve L9 represents light of 500nm in wavelength, and the broken lines L10 and L11 are used to represent the boundary positions of airy plaques. As can be seen from fig. 7, when 380nm light is used as the reference light, the objective lens 50 of the present embodiment can control the deviation of the converging point of the light with different wavelengths within the airy spot, and the chromatic aberration correction effect is better.

Accordingly, the embodiment of the present invention also provides an optical system including the objective lens 50 of the foregoing embodiment.

Based on the above analysis, the optical system integrated with the objective lens 50 has better detection performance, and can reduce the dependence on other optical compensation components.

Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention, and the scope of the invention should be assessed accordingly to that of the appended claims.

Claims (19)

1. An objective lens, comprising:

the lens group is used for converging parallel light beams with different wavelengths to one focus, and/or is used for enabling the light beams from the focus of the lens group to exit in parallel, and comprises a reflector group which is provided with at least one first reflecting surface;

at least one diffraction plane for scattering the light beam and reducing the dispersion of the objective lens.

2. The objective lens according to claim 1, wherein the lens group includes one or more lenses arranged in order in an optical axis direction, and at least one of the lenses has a diffraction surface, or the diffraction surface is a second reflection surface.

3. The objective of claim 1, wherein the mirror group is configured to image an object plane to be measured, and at least one first reflecting surface is a curved reflecting surface configured to focus a parallel incident beam to a focal point of the curved reflecting surface.

4. The objective lens according to claim 1, wherein the mirror group comprises at least two first reflecting surfaces, at least one first reflecting surface is a curved reflecting surface, and a turning mirror is further arranged in the at least two first reflecting surfaces, and the turning mirror is used for changing the imaging position of the mirror group, so that the imaging position of the mirror group and the focal point of the curved reflecting surface are respectively positioned at two sides of the curved reflecting surface; the curved surface reflecting surface and the turning reflecting mirror are oppositely arranged.

5. The objective lens according to claim 4, wherein a central region or an edge region of the first reflecting surface has a light passing region adapted to pass a light beam, and the central region is disposed at a position where an optical axis passes; the light beams from the outside of the reflector group are reflected to the turning reflector through the curved surface reflecting surface, and the light beams are reflected by the turning reflector and then emitted through the light passing area of the curved surface reflecting surface; or the light beams from the outside of the reflector group are reflected to the curved surface reflecting surface through the turning reflector, and the light beams are reflected by the curved surface reflecting surface and then emitted through the light passing area of the turning reflector.

6. The objective lens according to claim 3 or 4, wherein the lens group further comprises: and a refractive lens positioned between the two first reflecting surfaces, wherein the light path between the two first reflecting surfaces passes through the refractive lens for a plurality of times, and the refractive lens is used for increasing the numerical aperture of the objective lens.

7. Objective according to claim 1, characterized in that the number of the diffraction surfaces is two, the two diffraction surfaces being arranged opposite each other, or the lens group comprises one or more lenses arranged in succession in the direction of the optical axis, the two diffraction surfaces being separated by a part of the surface of the lens.

8. Objective according to claim 7, characterized in that two oppositely disposed diffraction surfaces are located on adjacent lenses, respectively.

9. Objective according to claim 1, characterized in that the plane of the diffraction plane is a plane.

10. Objective according to claim 1, characterized in that the diffraction surface comprises a plurality of concentric annular diffraction structures with the corresponding position of the optical axis as the centre of a circle, the direction from the centre of a circle to the edge of the lens, the spacing between adjacent diffraction structures decreases in sequence, and in case of a plurality of diffraction surfaces, the diffraction surface away from the object has a greater diffraction structure density.

11. The objective lens according to claim 1, wherein the lens group includes a focusing lens group, a field lens group, and an imaging lens group arranged in this order in an optical axis direction, at least one of the focusing lens group, the field lens group, and the imaging lens group includes the reflecting mirror, the focusing lens group and the imaging lens group are respectively located on both sides of an intermediate image plane in the optical axis direction, and the imaging lens group is closest to an object side, the field lens group is located in a preset position area between the focusing lens group and the imaging lens group, the imaging lens group is used for imaging an object plane to form an intermediate image in the intermediate image plane, the field lens group is adapted to perform chromatic aberration correction on a light beam passing through, and the preset position area includes a position of the intermediate image plane, and the focusing lens group is used for making a light beam from a point of the intermediate image plane exit in parallel.

12. Objective according to claim 11, characterized in that the lenses of the focusing lens group have the diffractive surface.

13. Objective according to claim 12, characterized in that in the focusing lens group, one or more lenses furthest from the object side in the optical axis direction have the diffractive surface.

14. The objective lens according to claim 11, wherein the focusing lens group includes, from an image side to an object side, a first plano-convex positive lens, a plano-concave negative lens, a first meniscus negative lens, a first biconvex positive lens, a second biconvex positive lens, and a second meniscus negative lens, which are arranged in order in an optical axis direction, and a plane of the first plano-convex positive lens, a concave surface of the plano-concave negative lens, a convex surface of the first meniscus negative lens, and a convex surface of the second meniscus negative lens are all directed toward the object side.

15. The objective lens according to claim 11, wherein the field lens group includes, from the image side to the object side, a third biconvex positive lens, a fourth biconvex positive lens, a biconcave negative lens, and a fifth biconvex positive lens, which are arranged in order in the optical axis direction.

16. The objective lens according to claim 11, wherein the imaging lens group includes, from an image side to an object side, a meniscus mirror, a third meniscus negative lens, and a second plano-convex positive lens arranged in this order in an optical axis direction, a concave surface of the meniscus mirror, a concave surface of the third meniscus negative lens, and a plane of the plano-convex lens all facing the object side, and a surface of the second meniscus negative lens facing the object side and a surface of the plane lens facing the object side all have the first reflection surface.

17. The objective lens of claim 11, wherein the focusing lens group includes a plurality of lenses having the same material, the field lens group includes a plurality of lenses having different materials, and the imaging lens group includes a plurality of lenses having the same material.

18. The objective of claim 17, wherein the material of the lenses in the focusing lens group comprises fused silica, the material of the lenses in the field lens group comprises fused silica and calcium fluoride, and the material of the lenses in the imaging lens group comprises fused silica.

19. An optical system comprising an objective lens according to any one of claims 1 to 18.