Deep ultraviolet objective lens and optical system

Abstract

The embodiment of the invention provides a deep ultraviolet objective lens and an optical system. The deep ultraviolet objective lens comprises a front group lens and a rear group lens; the front group lens is arranged close to an object plane, and the front group lens has positive diopter; and the rear group lens has negative diopter. The front group lens includes a refractive lens and at least one diffractive optical element to eliminate chromatic aberration.

Description

Technical Field

[0001] The present application relates to the field of optical technology, and in particular to a deep ultraviolet objective lens and an optical system. Background Art

[0002] In the field of deep ultraviolet objective lenses, the dispersion curve of commonly used materials changes faster than in the visible light field. For example, for fused quartz, at around 193 nanometers (nm), a wavelength change of 1nm causes a refractive index change of 0.0016, which is equivalent to a wavelength change of 38nm at around 532nm, resulting in large chromatic aberration. Chromatic aberration will affect the imaging quality of deep ultraviolet objective lenses. Summary of the invention

[0003] The purpose of this application is to provide a deep ultraviolet objective lens and an optical system that can reduce chromatic aberration to improve imaging quality.

[0004] To achieve the purpose of this application, this application provides the following technical solutions:

[0005] In a first aspect, an embodiment of the present application provides a deep ultraviolet objective lens, the deep ultraviolet objective lens comprising a front lens group and a rear lens group. The front lens group has a positive refractive power; the rear lens group has a negative refractive power. The front lens group comprises a refractive lens and at least one diffractive optical element.

[0006] The deep ultraviolet objective lens provided in the present application achieves achromatism due to the complementarity of the diffractive optical element and other refractive lenses in the deep ultraviolet objective lens, which is beneficial to improving the imaging quality and resolution of the deep ultraviolet objective lens.

[0007] According to the first aspect, in some possible implementations of the present application, the diffraction optical element includes a first surface and a second surface that are relatively arranged in the optical axis direction of the deep ultraviolet objective lens, the first surface is arranged away from the rear lens group, and at least one of the first surface and the second surface is a diffraction surface, the diffraction surface forms a plurality of diffraction bands, and the surface of the diffraction band includes at least four steps.

[0008] The diffractive optical element may be a step diffractive optical element. The diffractive band includes at least four steps. The more steps there are, the more conducive it is to improving the diffraction efficiency of the diffractive optical element, reducing light energy loss and improving energy utilization.

[0009] The diffraction optical element includes a first surface and a second surface which are arranged opposite to each other in the optical axis direction of the deep ultraviolet objective lens, the first surface is arranged away from the rear lens group, at least one of the first surface and the second surface is a diffraction surface, the diffraction surface includes a blazed grating surface, the diffraction surface forms a plurality of diffraction bands, and the surface of the diffraction band in the optical axis direction is a continuous surface.

[0010] The diffraction surface includes a blazed grating surface. Since the diffraction optical element is a continuous diffraction optical element, the diffraction band is a continuous surface, which is convenient for processing.

[0011] According to the first aspect, in some possible implementations of the present application, the diffraction surface is a harmonic diffraction surface, and the harmonic diffraction order of the harmonic diffraction surface is at least 2.

[0012] In this possible implementation, the etching depth of the microstructure on the surface of the ordinary diffraction element is increased, and its phase modulation function is changed so that the phase difference between adjacent ring zones is equal to an integer multiple of 2π.

[0013] According to the first aspect, in some possible implementations of the present application, in the direction of the optical axis, the refractive lens with the largest diameter in the front group of lenses is arranged on the side of the front group of lenses closest to the rear group of lenses, and at least one of the sides of the refractive lens with the largest diameter in the front group of lenses facing toward and away from the rear group of lenses is provided with at least one of the diffractive optical elements.

[0014] In this possible implementation, the diffractive optical element is arranged on the side of the seventh lens having the largest optical path diameter in the front lens group, which is beneficial to reducing the incident angle of light incident on the diffractive optical element, thereby facilitating improving the diffraction efficiency of the diffractive optical element.

[0015] According to the first aspect, in some possible implementations of the present application, the rear lens group includes at least one refractive lens and an aperture, and the aperture and the refractive lens of the rear lens group are arranged along the optical axis of the deep ultraviolet objective lens.

[0016] In this possible implementation, the aperture is used to limit the size of the light beam.

[0017] According to the first aspect, in some possible implementations of the present application, at least one refractive lens of the rear group of lenses includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens. Along the optical axis direction of the deep ultraviolet objective lens, the second lens is located between the first lens and the third lens, the third lens is located between the second lens and the fourth lens, the fourth lens is located between the third lens and the aperture, the aperture is located between the fourth lens and the fifth lens, and the fifth lens is located between the fourth lens and the sixth lens.

[0018] According to the first aspect, in some possible implementations of the present application, the first lens, the fourth lens, and the sixth lens are positive lenses, and the second lens and the third lens are negative lenses.

[0019] According to the first aspect, in some possible implementations of the present application, the refractive lens of the rear lens group is a spherical lens. Since spherical lenses have a uniform shape and a relatively simple processing process, the production cost is low.

[0020] According to the first aspect, in some possible implementations of the present application, the refractive lens in the front lens group is a positive spherical lens.

[0021] According to the first aspect, in some possible implementations of the present application, the refractive lens in the front lens group includes a seventh lens, an eighth lens, a ninth lens and a tenth lens. Along the optical axis direction of the deep ultraviolet objective lens, the seventh lens is arranged on the side of the front lens group closest to the rear lens group, the eighth lens is arranged between the seventh lens and the ninth lens, the ninth lens is arranged between the eighth lens and the tenth lens, and the diffractive optical element is arranged on at least one of the side of the seventh lens facing the rear lens group and between the seventh lens and the eighth lens.

[0022] According to the first aspect, in some possible implementations of the present application, the diffractive optical element is provided between the seventh lens and the eighth lens, and the surface parameters of the deep ultraviolet objective lens are as follows:

[0023] surface Remark Face type Material Curvature radius R[mm] S0 Incident surface Infinity S1 Infinity S2 L1 front surface STANDARD / Spherical NIFS-V 32.9267 S3 L1 rear surface STANDARD / Spherical 26.8984 S4 L2 front surface STANDARD / Spherical NIFS-V 110.3358 S5 L2 rear surface STANDARD / Spherical 36.7947 S6 L3 front surface STANDARD / Spherical NIFS-V 67.5487 S7 L3 rear surface STANDARD / Spherical 37.5656 S8 L4 front surface STANDARD / Spherical NIFS-V 221.6010 S9 L4 rear surface STANDARD / Spherical -136.2531 S10 stop Infinity S11 L5 front surface STANDARD / Spherical NIFS-V -51.3103 S12 L5 rear surface STANDARD / Spherical -68.2697 S13 L6 front surface STANDARD / Spherical NIFS-V -301.9177 S14 L6 rear surface STANDARD / Spherical -87.7386 S15 L7 front surface STANDARD / Spherical NIFS-V -2529.4195 S16 L7 rear surface STANDARD / Spherical -160.8592 S17 Front surface of DOE STANDARD NIFS-V Infinity S18 Back surface of DOE BINARY_2 Infinity S19 L8 front surface STANDARD / Spherical NIFS-V 56.9772 S20 L8 rear surface STANDARD / Spherical 90.4278 S21 L9 front surface STANDARD / Spherical NIFS-V 34.8584 S22 L9 rear surface STANDARD / Spherical 41.4434 S23 L10 front surface STANDARD / Spherical NIFS-V 35.0282 S24 L10 rear surface STANDARD / Spherical 52.5573 S25 STANDARD Infinity S26 exit surface STANDARD Infinity

[0024] In this possible implementation, at least one diffractive optical element is provided on a side of the seventh lens facing the rear lens group, and the above-mentioned surface design is used to improve the imaging quality while reducing energy loss.

[0025] According to the first aspect, in some possible implementations of the present application, at least one diffractive optical element is disposed on a side of the seventh lens facing the rear lens group and between the seventh lens and the eighth lens, and the surface parameters of the deep ultraviolet objective lens are as follows:

[0026]

[0027] In this possible implementation, at least one diffractive optical element is provided on a side of the seventh lens facing the rear lens group and between the seventh lens and the eighth lens, and the above-mentioned surface design is used to improve the imaging quality while reducing energy loss.

[0028] According to the first aspect, in some possible implementations of the present application, the material of the diffractive optical element is fused quartz.

[0029] According to the first aspect, in some possible implementations of the present application, the numerical aperture NA of the deep ultraviolet objective lens is ≥ 0.88.

[0030] In this possible implementation, the larger the numerical aperture NA of the deep ultraviolet objective lens is, the better its optical resolution k*λ / NA is.

[0031] According to the first aspect, in some possible implementations of the present application, the working distance of the deep ultraviolet objective lens is ≥7.8 mm.

[0032] In this possible implementation, when the sample is a photomask, the distance between the photomask and the mask pellicle is generally about 7.5 mm. The working distance of the deep ultraviolet objective lens is ≥ 7.8 mm, that is, the working distance of the deep ultraviolet objective lens is greater than the distance between the photomask and the mask pellicle. Due to the high optical resolution of the deep ultraviolet objective lens, the deep ultraviolet objective lens is suitable for detecting the photomask.

[0033] According to the first aspect, in some possible implementations of the present application, the working bandwidth of the deep ultraviolet objective lens is ≥10 pm.

[0034] According to the first aspect, in some possible implementations of the present application, the wave aberration of the deep ultraviolet objective lens is ≤0.02λ, where λ is the working wavelength of the deep ultraviolet objective lens, which is beneficial to improving the imaging quality and imaging effect of the deep ultraviolet objective lens.

[0035] According to the first aspect, in some possible implementations of the present application, the operating wavelength range of the deep ultraviolet objective lens is [193.358 nm, 193.378 nm].

[0036] In a second aspect, the present application provides an optical system, comprising a housing and a deep ultraviolet objective lens, wherein the deep ultraviolet objective lens is the deep ultraviolet objective lens provided according to the first aspect, and the deep ultraviolet objective lens is mounted in the housing. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram of an optical system provided by one embodiment of the present application;

[0038] Figure 2 is a schematic structural diagram of a deep ultraviolet objective lens provided in the first embodiment of the present application;

[0039] Figure 3 is a three-dimensional schematic diagram of a diffractive optical element provided in one embodiment of the present application;

[0040] Figure 4 yes Figure 3 A schematic cross-sectional view of a partial structure of a diffractive optical element shown;

[0041] Figure 5 is a schematic diagram of a step diffractive optical element provided in one embodiment of the present application;

[0042] Figure 6 and Figure 7 It is a schematic diagram of imaging optical simulation of a deep ultraviolet objective lens provided by the first embodiment when the working temperature is within the range of about 23°C;

[0043] Figure 8 is a schematic structural diagram of a deep ultraviolet objective lens provided in the second embodiment of the present application;

[0044] Fig. 9 and Fig.10 It is a schematic diagram of imaging optical simulation of a deep ultraviolet objective lens provided by the second embodiment within a working temperature range of about 23°C.

[0045] Description of reference numerals:

[0046] 100. optical system; 10. housing; 20. imaging module; 30. deep ultraviolet objective lens; 31. rear lens group; L1. first lens; L2. second lens; L3. third lens; L4. fourth lens; L5. fifth lens; L6. sixth lens; 401. aperture; 33. front lens group; L7. seventh lens; L8. eighth lens; L9. ninth lens; L10. tenth lens; 201. diffractive optical element; 301. diffractive zone; 3011. step; 2011. first diffractive optical element; 2012. second diffractive optical element; S0-S28. surface; 40. optical path switching module; 60. lighting module. DETAILED DESCRIPTION

[0047] Defects in the semiconductor integrated circuit manufacturing process have an increasingly greater impact on the performance and yield of integrated circuits. In the semiconductor integrated circuit process, effective control of defects is the key to ensuring yield and performance. In terms of defect detection, optical imaging detection is the main and fastest method. Semiconductor detection devices usually use objective lenses to detect defects in integrated circuits. Semiconductor detection devices can also detect masks, etc.

[0048] In the field of deep ultraviolet objective lenses, the dispersion curve of commonly used materials changes faster than in the visible light field. For example, for fused quartz, a wavelength change of 1nm near 193nm results in a refractive index change of 0.0016, which is equivalent to a wavelength change of 38nm near 532nm, resulting in large chromatic aberration. Chromatic aberration will affect the resolution of the objective lens.

[0049] In addition, in the deep ultraviolet field, the bandwidth of the light source is generally around 8 to 20 pm. The additional bandwidth narrowing process will cause a decrease in power and an increase in coherence. Therefore, achieving achromatism in the objective lens field is of great significance to improving the resolution of the objective lens.

[0050] Based on this, the present application provides a deep ultraviolet objective lens and a related optical system to reduce chromatic aberration and improve imaging quality. The deep ultraviolet objective lens includes a front lens group and a rear lens group. The front lens group has positive refractive power; the rear lens group has negative refractive power. The front lens group includes at least one diffractive optical element (DOE).

[0051] See also Figure 1 , Figure 1 The optical system 100 provided in one embodiment of the present application is a schematic diagram of the structure of the optical system 100, which can be used to detect defects of a sample. The sample can be a wafer or a photomask, etc., and the present application does not limit the type of the sample.

[0052] The optical system 100 includes a housing 10, an imaging module 20, a deep ultraviolet objective lens 30, an optical path switching module 40 and an illumination module 60. The housing 10 can be a sealed structure, and the housing 10 is enclosed and surrounded to form an inner cavity. The illumination module 60, the imaging module 20, the optical path switching module 40 and the objective lens 30 are all contained in the inner cavity. Among them, the deep ultraviolet objective lens 30 can be installed on the housing 10 and pass through the housing 10. The illumination module 60 is used to emit an illumination beam. The optical path switching module 40 is used to switch the illumination beam to the deep ultraviolet objective lens 30, and to irradiate the imaging beam to the imaging module 20, wherein the imaging beam is formed by the illumination beam passing through the deep ultraviolet objective lens 30 and then being reflected by the sample. The imaging module 20 may include an image sensor. The imaging module 20 performs microscopic imaging according to the imaging beam.

[0053] The optical system 100 may also be a semiconductor inspection device or a microscope.

[0054] It can be understood that the present application does not limit the specific architecture of the optical system 100. For example, the optical system 100 can omit the imaging module 20, the optical path switching module 40 and the lighting module 60; or, the optical system 100 can include an eyepiece and a deep ultraviolet objective lens 30, and the eyepiece is used to transform the inverted real image formed by the deep ultraviolet objective lens 30 into an upright, magnified virtual image.

[0055] See also Figure 2 The first embodiment of the present application provides a deep ultraviolet objective lens 30, which includes a front lens group 33 and a rear lens group 31. The deep ultraviolet objective lens 30 can be used Figure 1 In the optical system 100 shown.

[0056] In this embodiment, the front lens group 33 is arranged close to the object surface (object plane) S26, and the light beam is incident from the surface S0 side, that is, the surface S0 can be regarded as the incident surface, the surface S25 can be regarded as the exit surface of the deep ultraviolet objective lens 30, and the distance between the surface S25 and the object plane S26 can be the working distance (WD) of the deep ultraviolet objective lens 30. In other embodiments, the rear lens group 31 can also be arranged close to the object plane S26. The front lens group 33 has a positive refractive power. The rear lens group 31 has a negative refractive power. The rear lens group 31 includes a refractive lens. The front lens group 33 includes a refractive lens and at least one diffractive optical element 201. The refractive lens and the diffractive optical element 201 of the front lens group 33 are arranged along the optical axis direction of the deep ultraviolet objective lens 30.

[0057] Please refer to the achromatic formula (1):

[0058]

[0059] Among them, φ i is the focal power of the i-th element of the deep ultraviolet objective lens 30, v o is the Abbe number of the i-th element in the deep ultraviolet objective lens 30.

[0060] According to formula (1), if the optical system 100 needs to be achromatic, that is, the optical system 100 is dispersion-free, the diffractive optical element 201 needs to be complementary to other refractive lenses in the deep ultraviolet objective lens 30. The dispersion of the diffractive optical element 201 is independent of the material of the diffractive optical element 201, and the dispersion of the diffractive optical element 201 is related to the wavelength. The Abbe number of the diffractive optical element 201 is negative, that is, the Abbe number of the diffractive optical element 201 is opposite to that of the refractive lens, and the diffractive optical element and the refractive lens are complementary.

[0061] The deep ultraviolet objective lens 30 provided in the present application is a hybrid lens of a diffractive optical element 201 and a refractive lens. Since the diffractive optical element 201 and other refractive lenses in the deep ultraviolet objective lens 30 complement each other to achieve achromatism, it is beneficial to improve the imaging quality and resolution of the deep ultraviolet objective lens 30.

[0062] In some embodiments of the present application, the working wavelength λ range of the deep ultraviolet objective lens 30 is in the ultraviolet region between 100nm and 400nm, that is, the working wavelength λ range of the deep ultraviolet objective lens 30 is [100nm, 400nm]. For example, the working wavelength λ range can be [193.358nm, 193.378nm]. The numerical aperture (NA) of the deep ultraviolet objective lens 30 is ≥0.88. The working distance of the deep ultraviolet objective lens 30 is ≥7.8mm. The working bandwidth of the deep ultraviolet objective lens 30 is ≥10pm. The wave aberration of the deep ultraviolet objective lens 30 is ≤0.02λ. The working distance refers to the distance from the deep ultraviolet objective lens 30 to the surface to be detected of the sample.

[0063] The optical resolution formula of the deep ultraviolet objective lens 30 is: k*λ / NA, where k is a process factor. Theoretically, the minimum limit of exposure k is about 0.25. The larger the numerical aperture NA, the better the optical resolution. The numerical aperture NA of the deep ultraviolet objective lens 30 is ≥ 0.88, so that the deep ultraviolet objective lens 30 can obtain high optical resolution.

[0064] Wave aberration refers to the phenomenon that the wavefront of light in an optical system is distorted. The smaller the wave aberration, the higher the imaging quality. The wave aberration of the deep ultraviolet objective lens 30 provided in the present application is ≤0.02λ, which can improve the imaging effect and quality of the deep ultraviolet objective lens 30.

[0065] When the sample is a photomask, the distance between the photomask and the mask pellicle is generally about 7.5 mm. The working distance of the deep ultraviolet objective lens 30 is ≥ 7.8 mm, that is, the working distance of the deep ultraviolet objective lens 30 is greater than the distance between the deep ultraviolet objective lens 30 and the mask pellicle. Since the deep ultraviolet objective lens 30 can eliminate chromatic aberration by setting the diffractive optical element 201, the optical resolution of the deep ultraviolet objective lens 30 is high, and the deep ultraviolet objective lens 30 is suitable for detecting photomasks.

[0066] It can be understood that the present application does not limit the numerical aperture range of the deep ultraviolet objective lens 30 , the present application does not limit the working distance range of the deep ultraviolet objective lens 30 , and the present application does not limit the working bandwidth range of the deep ultraviolet objective lens 30 .

[0067] It is understood that the technical solution provided in this application can also be applied to other objective lenses, such as microscope objective lenses, and this application does not limit the working wavelength of deep ultraviolet objective lenses. In this embodiment, the diffractive optical element 201 is made of fused quartz material, and other refractive lenses in the deep ultraviolet objective lens 30 can be made of fused quartz or calcium fluoride material.

[0068] The diffractive optical element 201 includes a first surface S18 and a second surface S17 which are disposed opposite to each other in the optical axis direction of the deep ultraviolet objective lens 30, and the first surface S18 is disposed away from the rear lens group 31. The first surface S18 is a diffractive surface.

[0069] In some embodiments of the present application, the diffractive optical element 201 can be used as a binary (diffractive) optical element (BINARY2), and the surface shape of the diffractive surface can be called BINARY2. The binary (diffractive) optical element is a multi-order phase structure. The ideal continuous phase profile is quantized by 2 and made into a step-like approximation, so it is called a binary (diffractive) optical element. The binary (diffractive) optical element has the characteristics of small size, light weight, easy array integration and mass replication. For details, please refer to Figure 3 and Figure 4 The diffraction surface forms a plurality of diffraction bands 301, and the diffraction optical element 201 may be a step diffraction optical element. The diffraction band 301 includes at least four steps 3011. The more steps 3011 there are, the higher the diffraction efficiency of the diffraction optical element 201 is. For example, the efficiency of 8 steps 3011 can reach 95% at most, and the efficiency of 16 steps 3011 can reach 99% at most.

[0070] In some embodiments of the present application, the diffraction surface of the diffraction optical element 201 may be a blazed grating surface, the outer surface of the diffraction band 301 is a non-step structure, and the outer surface of the diffraction band 301 in the optical axis direction is a continuous surface. In this case, the diffraction optical element 201 may be referred to as a continuous diffraction optical element. Blazed gratings, also known as small step gratings, are a specific reflection or projection diffraction grating structure that produces maximum diffraction efficiency at a specific diffraction level. This means that the optical power is concentrated as much as possible on the preset diffraction level, while the loss of optical power at other levels (especially the zeroth order) is minimized. Figure 5 The abscissa of is the radius of the diffractive optical element, Figure 5 The ordinate is the phase (0 to 2π), Figure 5 The radius and phase are for exemplary purposes only and do not constitute a limitation to the present application.

[0071] The diffraction surface satisfies the phase function represented by the following formula (2):

[0072] phi=M∑ i A i ·ρ 2i , (2)

[0073] Wherein, M is the diffraction order, generally ±1, Ai is the phase coefficient, ρ is the normalized radius coefficient, specifically the actual radius / normalized radius of the diffractive optical element 201. In this embodiment, as shown in Table 1, they represent the coefficient values ​​of the 2nd order term, 4th order term, and 6th order term, respectively.

[0074] Table 1

[0075] Normalized radius / mm 100 <![CDATA[ρ 2 The coefficient of A2]]> -1.24E+06 <![CDATA[ρ 4 The coefficient of A4]]> -1.12E+05 <![CDATA[ρ 6 The coefficient of A6]]> -2.53E+05

[0076] It can be understood that the second surface S17 can also be set as a diffraction surface.

[0077] In some embodiments of the present application, the diffractive optical element 201 may be a harmonic diffractive optical element (HDOE), and at least one of the first surface S18 and the second surface S17 forms a harmonic diffraction surface with a harmonic diffraction order of at least 2.

[0078] The diffractive optical element can be a step-type or a continuous-surface-type diffractive optical element. Figure 4 or Figure 5 The diffractive optical element shown in the example is taken as an example of a common diffractive optical element. Assume that the height of the diffraction zone of the common diffractive optical element is d 0 , let the distance between the diffraction zone closest to the center of the ordinary diffractive optical element and the center be r 01 The diffraction surface of the harmonic diffractive optical element may include a diffraction band, and the diffraction band includes at least four steps. Alternatively, the diffraction surface is a continuous surface. When the diffractive optical element 201 is a harmonic diffractive optical element, the height of the diffraction band (diffraction band) of the harmonic diffractive optical element is set to D 0 , let the distance between the ring zone closest to the center of the harmonic diffractive optical element and the center be R 01 , D 0 =N·d 0 ; R 01 =N·r 01 , N is a positive integer.

[0079] The harmonic diffraction element increases the etching depth of the surface microstructure of the ordinary diffraction element and changes its phase modulation function so that the phase difference between adjacent ring zones (diffraction zones) is equal to an integer multiple of 2π. Compared with ordinary diffraction optical elements, the diffraction efficiency of the harmonic diffraction element will be higher.

[0080] Please refer again Figure 2, the rear lens group 31 includes at least one refractive lens and a stop 401. The stop 401 is used to limit the size of the light beam. In one embodiment, the refractive lens of the rear lens group 31 includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5 and a sixth lens L6. Along the optical axis direction of the deep ultraviolet objective lens 30, the first lens L1 is arranged on the side of the rear lens group 31 farthest from the front lens group 33, and the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the stop 401, the fifth lens L5 and the sixth lens L6 are arranged in sequence. That is, along the optical axis direction of the deep ultraviolet objective lens 30, the second lens L2 is located between the first lens L1 and the third lens L3, the third lens L3 is located between the second lens L2 and the fourth lens L4, the fourth lens L4 is located between the third lens L3 and the stop, the stop is located between the fourth lens L4 and the fifth lens L5, and the fifth lens L5 is located between the fourth lens L4 and the sixth lens L6. The first lens L1, the fourth lens L4, and the sixth lens L6 are positive lenses, and the second lens L2 and the third lens L3 are negative lenses. The first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 are all spherical lenses. A spherical lens refers to a lens whose front and back surfaces are both parts of a spherical surface, and the curvature of the spherical surface is fixed. Since the shape of spherical lenses is uniform and the processing process is relatively simple, the production cost is low.

[0081] It can be understood that the present application does not limit the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 to be spherical lenses. Each of the first lens L1, the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5 and the sixth lens L6 can be a spherical lens or an aspherical lens.

[0082] It can be understood that the present application does not limit the number of refractive lenses of the rear lens group 31 , and the rear lens group 31 may include at least one refractive lens, and the rear lens group 31 only needs to have negative refractive power.

[0083] In one embodiment, the refractive lens of the front lens group 33 includes a seventh lens L7, an eighth lens L8, a ninth lens L9 and a tenth lens L10. Optionally, along the optical axis direction of the deep ultraviolet objective lens 30, the seventh lens L7 is disposed on the side of the front lens group 33 closest to the rear lens group 31, and the seventh lens L7, the diffractive optical element 201, the eighth lens L8, the ninth lens L9 and the tenth lens L10 are disposed in sequence. The seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10 are all spherical lenses. The seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10 are all positive lenses.

[0084] It can be understood that the present application does not limit the seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10 to be spherical lenses, and each of the seventh lens L7, the eighth lens L8, the ninth lens L9 and the tenth lens L10 can be one of a spherical lens and an aspherical lens.

[0085] In this embodiment, the seventh lens L7 is a refractive lens with the largest diameter in the rear lens group 31. The diffractive optical element 201 is arranged on the side of the seventh lens L7 with the largest optical path diameter in the front lens group 33, which is conducive to reducing the incident angle of the light beam incident on the diffractive optical element 201, thereby facilitating the improvement of the diffraction efficiency of the diffractive optical element 201. In this embodiment, the diameter of the diffractive optical element 201 is also greater than the diameters of the eighth lens L8, the ninth lens L9 and the tenth lens L10.

[0086] It can be understood that the diffractive optical element 201 can also be arranged on the side of the seventh lens L7 facing the rear lens group 31.

[0087] It can be understood that the present application does not limit the height at which the light beam is incident on the diffractive optical element 201 .

[0088] It can be understood that the present application does not limit the specific structure of the front lens group 33 , and the front lens group 33 only needs to include at least one diffractive optical element 201 .

[0089] It can be understood that the number of refractive lenses in the front lens group 33 can be one. In some embodiments, the refractive lens with the largest height in the front lens group 33 is arranged on the side of the front lens group 33 closest to the rear lens group 31, and a diffractive optical element 201 is provided on the side of the refractive lens with the largest height in the front lens group 33 facing or away from the rear lens group 31.

[0090] In some embodiments of the present application, the lens design parameters in the deep ultraviolet objective lens 30 are shown in Table 2. The material of the diffractive optical element 201 is fused quartz, and NIFS-V in Table 2 represents fused quartz. STANDARD is a standard surface type, and STANDARD is a plane or a spherical surface. Surfaces S0-S26 are surfaces of each lens of the deep ultraviolet objective lens 30, and S0, S1, S25, and S26 can be virtual surfaces. See Table 2 below for details. In Table 2, in the optical axis direction of the deep ultraviolet objective lens 30, the front surface is the surface of the optical element away from the object plane, and the rear surface of the deep ultraviolet objective lens 30 is the surface of the optical element facing the object plane.

[0091] Table 2

[0092]

[0093]

[0094] See also Figure 6 and Figure 7 , Figure 6 The horizontal axis is the field of view value (+YField Degrees). Figure 8 The vertical axis in is the RMS wavefront error value (RMSwavefront Error in Waves). Figure 6 It is the comprehensive wave aberration of the deep ultraviolet objective lens 30 when the working temperature is approximately 23°C, A, B, C, D, E, and F respectively represent the wave aberrations of ultraviolet wavelengths 193.358 / 193.362 / comprehensive / 193.368 / 193.378 / 193.374 within the working temperature range of 23°C, where comprehensive is the average of the RMS wave aberrations of the remaining five wavelengths. Figure 7 IMA is the position of the exit surface, and OBJ is the angle of incidence. According to the simulation results, the deep ultraviolet objective lens 30 achieves a comprehensive wave aberration of ≤0.01λ in the wavelength range of 193.358nm / 193.362 / 193.368 / 193.374 / 193.378nm when the working temperature is approximately 23°C. It can be seen that the deep ultraviolet objective lens 30 of the present application can still achieve a low comprehensive wave aberration value at a long working distance of not less than 7.8mm and a working bandwidth of not less than 10pm, which is beneficial to improving the imaging quality and imaging effect.

[0095] See also Figure 8 The second embodiment of the present application provides a deep ultraviolet objective lens 30. The deep ultraviolet objective lens 30 provided in the second embodiment is different from the deep ultraviolet objective lens 30 provided in the first embodiment in that, in the optical axis direction, diffractive optical elements are provided on both sides of the seventh lens L7, that is, diffractive optical elements are provided between the sixth lens L6 and the seventh lens L7, and between the seventh lens L7 and the eighth lens L8. The two diffractive optical elements include a first diffractive optical element 2011 (labeled as DOE1 in Table 4) and a second diffractive optical element 2012 (labeled as DOE2 in Table 4). The first surfaces of the first diffractive optical element 2011 and the second diffractive optical element 2012 are both diffractive surfaces. The diffractive surfaces satisfy the phase function represented by formula (2).

[0096] In this embodiment, as shown in Table 3, they represent the coefficient values ​​of the 2nd order term, the 4th order term, and the 6th order term, respectively.

[0097] Table 3

[0098] DOE1(2011) DOE1(2012) Normalized radius / mm 100 1.00E+02 <![CDATA[ρ 2 Coefficient A2]]> -6.91E+05 -5.58E+05 <![CDATA[ρ 4 Coefficient A4]]> 6.09E+04 -1.18E+05 <![CDATA[ρ 6 Coefficient A6]]> 1.95E+05 1.20E+00

[0099] In some embodiments of the present application, on the diffraction surface of the diffraction optical element, multiple diffraction bands are concentrically arranged with the center of the diffraction surface. The more diffraction bands there are, the smaller the minimum annular band width of the diffraction bands is, making the diffraction optical element more difficult to process. Providing two diffraction optical elements is equivalent to separately arranging multiple diffraction bands on a diffraction surface of a diffraction optical element on the diffraction surfaces of two diffraction optical elements. In this way, the minimum annular band width will increase with the increase of the number of diffraction elements used, making it easier to process.

[0100] It can be understood that the number of diffractive optical elements can be maintained at one, and the first surface and the second surface of the diffractive optical element are both diffractive surfaces, which is equivalent to separately arranging multiple diffraction bands on a diffraction surface of a diffractive optical element on two diffraction surfaces of the same diffractive optical element. In this way, the minimum ring band width will increase with the increase of the diffraction elements used, and it will become easier to process.

[0101] It can be understood that at least one of the first surface and the second surface is configured as a diffraction surface.

[0102] It can be understood that the present application does not limit the number of refractive lenses in the front lens group 33. In the direction of the optical axis, the refractive lens with the largest diameter in the front lens group 33 is arranged on the side of the front lens group 33 closest to the rear lens group 31, and at least one of the sides of the refractive lens with the largest diameter in the front lens group 33 facing toward and away from the rear lens group 31 is provided with a diffractive optical element.

[0103] In some embodiments of the present application, the design parameters of the deep ultraviolet objective lens 30 are shown in Table 4. Surfaces S0-S28 are surfaces of each lens of the deep ultraviolet objective lens 30. S0, S1, S27, and S28 can be virtual surfaces. In Table 4, in the optical axis direction of the deep ultraviolet objective lens 30, the front surface is the surface of the optical element away from the object plane of the deep ultraviolet objective lens 30, and the rear surface is the surface of the optical element facing the object plane.

[0104] Table 4

[0105]

[0106] See also Fig. 9 and Fig.10 , Fig. 9 The horizontal axis is the field of view value (+YField Degrees). Fig.10 The vertical axis in is the RMS wavefront error value (RMSwavefront Error in Waves). Fig. 9It is the comprehensive wave aberration of the deep ultraviolet objective lens 30 when the working temperature is approximately 23°C, A, B, C, D, E, and F respectively represent the wave aberrations of ultraviolet wavelengths 193.358 / 193.362 / comprehensive / 193.368 / 193.378 / 193.3749 within the working temperature range of 23°C, where comprehensive is the average of the RMS wave aberrations of the remaining five wavelengths. Fig.10 IMA is the position of the exit surface, and OBJ is the angle of incidence. According to the simulation results, the deep ultraviolet objective lens 30 achieves a comprehensive wave aberration of ≤0.02λ in the wavelength range of 193.358nm / 193.362 / 193.368 / 193.374 / 193.378nm within the working temperature range of 23°C. It can be seen that the deep ultraviolet objective lens 30 of the present application can still achieve a low comprehensive wave aberration value at a long working distance of not less than 7.8mm and a working bandwidth of not less than 10pm, which is beneficial to improving the imaging quality and imaging effect.

[0107] In the description of the implementation methods of the present application, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0108] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there can be a central component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there can be a central component at the same time.

[0109] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items.

[0110] What is disclosed above is only a preferred implementation of the present application, and it certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above implementation and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A deep ultraviolet objective lens (30), characterized in that: The deep ultraviolet objective lens (30) comprises a front lens group (33) and a rear lens group (31); the front lens group (33) has a positive refractive power; the rear lens group (31) has a negative refractive power; The front lens group (33) includes a refractive lens and at least one diffractive optical element (201).

2. The deep ultraviolet objective lens (30) according to claim 1, characterized in that: The diffraction optical element (201) includes a first surface and a second surface which are arranged opposite to each other in the optical axis direction of the deep ultraviolet objective lens (30), the first surface is arranged away from the rear lens group (31), at least one of the first surface and the second surface is a diffraction surface, the diffraction surface forms a plurality of diffraction bands (301), and the surface of the diffraction bands (301) includes at least four steps (3011).

3. The deep ultraviolet objective lens (30) according to claim 1, characterized in that: The diffraction optical element (201) comprises a first surface and a second surface which are arranged opposite to each other in the optical axis direction of the deep ultraviolet objective lens (30), the first surface being arranged away from the rear lens group (31), at least one of the first surface and the second surface being a diffraction surface, the diffraction surface comprising a blazed grating surface, the diffraction surface forming a plurality of diffraction bands (301), and the surface of the diffraction bands (301) in the optical axis direction is a continuous surface.

4. The deep ultraviolet objective lens (30) according to claim 2 or 3, characterized in that: The diffraction surface is a harmonic diffraction surface, and the harmonic diffraction order of the harmonic diffraction surface is at least 2.

5. The deep ultraviolet objective lens (30) according to any one of claims 1 to 4, characterized in that: In the direction of the optical axis, the refractive lens with the largest diameter in the front lens group (33) is arranged on the side of the front lens group (33) closest to the rear lens group (31), and at least one of the sides of the refractive lens with the largest diameter in the front lens group (33) facing toward and away from the rear lens group (31) is provided with at least one of the diffractive optical elements (201).

6. The deep ultraviolet objective lens (30) according to any one of claims 1 to 5, characterized in that: The rear lens group (31) comprises at least one refractive lens and an aperture (401), and the aperture (401) and the refractive lens of the rear lens group (31) are arranged along the optical axis of the deep ultraviolet objective lens (30).

7. The deep ultraviolet objective lens (30) according to claim 6, characterized in that: At least one refractive lens of the rear lens group (31) includes a first lens (L1), a second lens (L2), a third lens (L3), a fourth lens (L4), a fifth lens (L5) and a sixth lens (L6). Along the optical axis direction of the deep ultraviolet objective lens (30), the second lens (L2) is located between the first lens (L1) and the third lens (L3), the third lens (L3) is located between the second lens (L2) and the fourth lens (L4), the fourth lens (L4) is located between the third lens (L3) and the aperture (401), the aperture (401) is located between the fourth lens (L4) and the fifth lens (L5), and the fifth lens (L5) is located between the fourth lens (L4) and the sixth lens (L6).

8. The deep ultraviolet objective lens (30) according to claim 7, characterized in that: The first lens (L1), the fourth lens (L4), and the sixth lens (L6) are positive lenses, and the second lens (L2) and the third lens (L3) are negative lenses.

9. The deep ultraviolet objective lens (30) according to claim 6, characterized in that: The refractive lens of the rear lens group (31) is a spherical lens.

10. The deep ultraviolet objective lens (30) according to claim 6, characterized in that: The refractive lenses in the front lens group (33) include a seventh lens (L7), an eighth lens (L8), a ninth lens (L9) and a tenth lens (L10); Along the optical axis direction of the deep ultraviolet objective lens (30), the seventh lens (L7) is arranged on the side of the front lens group (33) closest to the rear lens group (31), the eighth lens (L8) is located between the seventh lens (L7) and the ninth lens (L9), and the ninth lens (L9) is located between the eighth lens (L8) and the tenth lens (L10), and at least one of the side of the seventh lens (L7) facing the rear lens group (31) and between the seventh lens (L7) and the eighth lens (L8) is provided with at least one of the diffractive optical element (201).

11. The deep ultraviolet objective lens (30) according to claim 10, characterized in that: The diffractive optical element (201) is provided between the seventh lens (L7) and the eighth lens (L8), and the surface parameters of the deep ultraviolet objective lens (30) are as follows:

12. The deep ultraviolet objective lens (30) according to claim 10, characterized in that: At least one diffractive optical element (201) is disposed on the side of the seventh lens (L7) facing the rear lens group (31) and between the seventh lens (L7) and the eighth lens (L8), and the surface parameters of the deep ultraviolet objective lens (30) are as follows:

13. The deep ultraviolet objective lens (30) according to any one of claims 1 to 10, characterized in that: The refractive lens in the front lens group (33) is a positive spherical lens.

14. The deep ultraviolet objective lens (30) according to any one of claims 1 to 10, characterized in that: The material of the diffractive optical element (201) is fused quartz.

15. The deep ultraviolet objective lens (30) according to any one of claims 1 to 14, characterized in that: The numerical aperture NA of the deep ultraviolet objective lens (30) is ≥ 0.

88.

16. The deep ultraviolet objective lens (30) according to claim 15, characterized in that: The working distance of the deep ultraviolet objective lens (30) is ≥7.8 mm.

17. The deep ultraviolet objective lens (30) according to any one of claims 1 to 16, characterized in that: The working bandwidth of the deep ultraviolet objective lens (30) is ≥10 pm.

18. The deep ultraviolet objective lens (30) according to any one of claims 1 to 17, characterized in that: The wave aberration of the deep ultraviolet objective lens (30) is ≤0.02λ, and λ is the working wavelength of the deep ultraviolet objective lens (30).

19. The deep ultraviolet objective lens (30) according to any one of claims 1 to 18, characterized in that: The operating wavelength range of the deep ultraviolet objective lens (30) is [193.358 nm, 193.378 nm].

20. An optical system (100), characterized in that: The optical system (100) comprises a housing and a deep ultraviolet objective lens (30), wherein the deep ultraviolet objective lens (30) is the deep ultraviolet objective lens (30) according to any one of claims 1 to 19, and the deep ultraviolet objective lens (30) is mounted on the housing (10).

Images