Sample measurement system and lithographic apparatus

Abstract

The present invention provides a sample measurement system and a lithographic apparatus wherein the sample measurement system comprises: an illumination unit for providing a broadband light source; the telephoto illumination lens group is used for collimating a broadband light source or reducing wavefront phase differences of different wavelengths; the flat-field apochromatic diffraction objective lens is used for reducing longitudinal focal shift or odd-order wave aberration of the broadband light source passing through the telephoto illumination lens group; the detection unit is used for detecting an image formed on the sample by the broadband light source passing through the flat-field apochromatic diffraction objective lens to obtain an optical signal; and the information processing unit is used for processing the obtained optical signal to obtain a processing result. According to the sample measurement system provided by the invention, Gaussian beams with different wavelengths can meet the wavefront aberration requirement of the measurement system, and meanwhile, the longitudinal focal shift and the odd-order wave aberration can be reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical technology, and in particular to a sample measurement system and a photolithography device. Background Art

[0002] The photolithography equipment in the prior art is mainly used for manufacturing integrated circuits (ICs) or other micro devices. Through the photolithography equipment, multiple layers of masks with different mask patterns are sequentially exposed and imaged on a silicon wafer coated with photoresist under precise alignment.

[0003] In the alignment system, the wide-band 4f optical system based on laser transmission suffers from large chromatic aberration on the silicon wafer surface.

[0004] In order to reduce chromatic aberration, patent application CN 103499871 discloses a super-achromatic optical system for measuring the divergence angle of a laser beam. This patent application is used for measuring the divergence angle of a laser beam, and the measurement accuracy can meet the requirements. The optical aperture of 150mm can meet the measurement of the divergence angle of a beam with a large spot size. The telephoto optical structure is used to make the total length less than the focal length, reducing the volume. Moreover, the MTF value of the optical transfer function curve at each frequency is close to the diffraction limit, achieving the purpose of achromatic aberration. However, this patent application is mainly used for measuring the divergence angle of a laser beam, with a long focal length and length, and a large aperture, which is not suitable for use in lighting systems for precision measurement in small spaces. This patent application is used for achromatic aberration in the 350nm to 1600nm band. In the design, the spherical aberration at the full aperture is guaranteed to be 0.0676mm, and the light of 355nm, 532nm, 660nm, 808nm, 940nm, 1064nm, 1319nm, and 1570nm basically intersects at one point at an aperture of 0.707. Moreover, the design only considers the correction of geometric aberrations, and does not take into account the characteristics of Gaussian beam propagation. The amount of secondary spectrum elimination is far from meeting the high-precision measurement indicators used in lithography machines, and cannot meet the requirements for full-aperture secondary spectrum elimination.

[0005] Patent application CN 108292038 B discloses an illumination optical path. The patent application relates to an objective lens in a self-reference alignment system of a photolithography machine, which includes, from the object side, the following: a coma correction element caused by centrifugation; a first lens element group, configured and arranged to correct field-dependent aberrations; a second lens element group, configured and arranged to correct high-order chromatic aberrations; a third lens element group, configured and arranged to correct low-order chromatic aberrations; and a fourth lens element group, having positive optical power. The overall optical power distribution is negative, negative, positive, negative, and positive. Light with a wavelength between 500nm and 900nm satisfies the following conditions: NA is greater than about 0.6, usually 0.68<NA<0.72, PV odd wavefront error is less than about 8nm and preferably less than about 5nm, working distance is greater than about 6mm, preferably greater than about 8mm, and longitudinal focal shift is about 0.196um. The longitudinal focal shift of the patent application is relatively large, and CaF2 is used as the main achromatic glass in the design. CaF2 glass is soft, difficult to process, and has poor resistance to deliquesce, acid and alkali. Summary of the invention

[0006] The object of the present invention is to provide a sample measurement system and a photolithography device to reduce longitudinal focal shift and odd-order wave aberrations.

[0007] In order to achieve the above object and other related objects, the present invention provides a sample measurement system, comprising:

[0008] A lighting unit, used for providing a broadband light source;

[0009] Telephoto illumination lens set, used for collimating wide-band light sources or reducing wavefront phase differences of different wavelengths;

[0010] A plan apochromatic diffraction objective lens is used to reduce longitudinal focal shift or odd-order wave aberration for a wide-band light source passing through the telephoto illumination lens assembly;

[0011] A detection unit, detecting an image formed on the sample by the wide-band light source passing through the plan apochromatic diffraction objective lens to obtain a light signal;

[0012] The information processing unit processes the obtained optical signal to obtain a processing result.

[0013] Optionally, in the sample measurement system, the telephoto illumination lens group includes, in sequence from one side of the object plane along the optical axis: a first double cemented lens with negative optical power, a first meniscus negative lens, a first negative lens and a first biconvex positive lens.

[0014] Optionally, in the sample measurement system, the plan apochromatic diffraction objective has a lens group with optical powers of positive, positive, negative, and positive, respectively.

[0015] Optionally, in the sample measurement system, the plan apochromatic diffraction objective lens includes, in order from one side of the object plane along the optical axis:

[0016] A first lens element group, composed to correct field-dependent aberrations;

[0017] The second lens element group is composed of corrected high-order chromatic spherical aberrations;

[0018] The third lens element group is composed of corrected low-order chromatic spherical aberrations;

[0019] The fourth lens element group forms a positive focal power group that meets the requirements of large numerical aperture and long working distance.

[0020] Optionally, in the sample measurement system, the relationship between the focal length of each lens in the telephoto lighting lens assembly and the total focal length is:

[0021] -1.3 <f 1 / f<-0.6;

[0022] -1.9 <f 2 / f<-1.3;

[0023] -1.6 <f 3 / f<-1;

[0024] 0.1 <f 4 / f<0.6;

[0025] where f 1 is the focal length of the first doublet lens, f 2 is the focal length of the first meniscus negative lens, f 3 is the focal length of the first negative lens, f 4 is the focal length of the first biconvex positive lens, and f is the total focal length of the telephoto lighting lens assembly.

[0026] Optionally, in the sample measurement system, the first lens element group includes, in sequence from one side of the object plane along the optical axis, a second meniscus negative lens and a second biconvex positive lens matched therewith; the second lens element group includes a second double-cemented lens and a third double-cemented lens, both of which are combinations of low-dispersion material and ultra-high-dispersion material, and are both cemented lenses with weak positive optical power; the third lens element group includes a fourth double-cemented lens, and the fourth double-cemented lens has negative optical power as a whole; the fourth lens element group includes three lenses with positive optical power, and the three lenses with positive optical power are made of low-dispersion material.

[0027] Optionally, in the sample measurement system, the relationship between the focal length of each lens in the plan apochromatic diffraction objective and the total focal length is:

[0028] 8 <f1 ' / f'<12;

[0029] 3 <f 2 ' / f'<5;

[0030] -3 <f 3 ' / f'<-2;

[0031] 0.4 <f 4 ' / f'<1.5;

[0032] where f 1 ' is the focal length of the first lens element group, f 2 ' is the focal length of the second lens element group, f 3 ' is the focal length of the third lens element group, f 4 ' is the focal length of the fourth lens element group, and f' is the total focal length of the plan apochromatic diffractive objective lens.

[0033] Optionally, in the sample measurement system, the relationship between the focal length of the lens in the telephoto illumination lens assembly and the total focal length is:

[0034] -1 <f 1 / f<-0.1;

[0035] -1.1 <f 2 / f<-0.2;

[0036] -5 <f 3 / f<-3.5;

[0037] 0 <f 4 / f<0.7;

[0038] where f 1 is the focal length of the first doublet lens, f 2 is the focal length of the first meniscus negative lens, f 3 is the focal length of the first negative lens, f 4 is the focal length of the first biconvex positive lens, and f is the total focal length of the telephoto lighting lens assembly.

[0039] Optionally, in the sample measurement system, the first lens element group includes, from the object plane side, a second meniscus negative lens and a second biconvex positive lens matched therewith; the second lens element group includes a second double-cemented lens and a positive lens; the third lens element group includes a third double-cemented lens, and the third double-cemented lens has a negative optical focal length as a whole; and the fourth lens element group includes three positive lenses.

[0040] Optionally, in the sample measurement system, the relationship between the focal length of the lens in the plan apochromat objective and the total focal length is:

[0041] 5 <f 1 ' / f'<10;

[0042] 5 <f 2 ' / f'<8;

[0043] -2.6 <f 3 ' / f'<-1.6;

[0044] 0.4 <f 4 ' / f'<1.4;

[0045] where f 1 ' is the focal length of the first lens element group, f 2 ' is the focal length of the second lens element group, f 3 ' is the focal length of the third lens element group, f 4 ' is the focal length of the fourth lens element group, and f' is the total focal length of the plan apochromatic diffractive objective lens.

[0046] Optionally, in the sample measurement system, the broadband light source is a laser beam.

[0047] Optionally, in the sample measurement system, a light-cutting diaphragm is provided on one side of the object plane of the telephoto illumination objective lens, and the position of the light-cutting diaphragm coincides with the beam waist position of the laser beam.

[0048] In order to achieve the above object and other related objects, the present invention also provides a lithography device, including the sample measurement system described above.

[0049] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0050] The sample measurement system provided by the present invention includes a telephoto illumination lens group and a plan-apochromatic diffraction objective lens, wherein the telephoto illumination lens group is used for collimating a wide-band light source or reducing the wavefront phase difference of different wavelengths; the plan-apochromatic diffraction objective lens reduces the longitudinal focal shift or reduces the odd-order wave aberration of the wide-band light source passing through the telephoto illumination lens group. The present invention can make Gaussian beams of different wavelengths meet the wavefront aberration requirements of the measurement system through the arrangement of the telephoto illumination lens group and the plan-apochromatic diffraction objective lens, while reducing the longitudinal focal shift and the odd-order wave aberration. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a schematic structural diagram of a telephoto illumination lens assembly and a plan-apochromatic diffraction objective lens assembly according to an embodiment of the present invention;

[0052] Figure 2 is a structural schematic diagram of a telephoto lighting lens assembly according to an embodiment of the present invention;

[0053] Figure 3 1 is a schematic structural diagram of a plan apochromatic diffraction objective lens according to an embodiment of the present invention;

[0054] Figure 4 is a graph showing the relationship between the longitudinal focal shift and the aperture of a plan apochromatic diffraction objective lens according to an embodiment of the present invention;

[0055] Figure 5 It is a schematic structural diagram of a telephoto illumination lens assembly and a plan-apochromatic diffraction objective lens assembly according to another embodiment of the present invention;

[0056] Figure 6 is a schematic structural diagram of a telephoto lighting lens assembly according to another embodiment of the present invention;

[0057] Figure 7 is a schematic structural diagram of a plan apochromatic diffraction objective lens according to another embodiment of the present invention;

[0058] Figure 8 4 is a relationship diagram between the longitudinal focal shift and the aperture of a plan apochromatic diffraction objective lens according to another embodiment of the present invention. DETAILED DESCRIPTION

[0059] The sample measurement system and lithography apparatus proposed in the present invention are further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer according to the following description. It should be noted that the accompanying drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0060] At present, in most laser applications, due to the existence of laser divergence angle, the laser beam must be collimated. The laser emitted by the stable laser cavity laser is transmitted in space in the form of a Gaussian beam. Assuming that the laser beam has an ideal Gaussian light intensity distribution (M2 = 1), it is usually calculated by theoretical TEM. 00 The pattern describes the propagation law of Gaussian beams in the lens. Different from the propagation theory of geometric optics, the propagation of Gaussian beams follows the Fresnel-Kirchhoff diffraction integral equation. The propagation of Gaussian beams through the lens group cannot be evaluated by the image quality evaluation parameters of geometric optics. The main evaluation index of the propagation of Gaussian beams through the lens is the change of the wavefront reaching the image plane.

[0061] The fundamental mode Gaussian beam propagating along the z-axis can be expressed as:

[0062]

[0063]

[0064] Where k and c are constants, i is a negative parameter, ω 0is the waist radius of the incident light beam, ω(z) is the waist radius of the light beam at position z, z is the propagation distance, f is the focal length of the object, f' is the focal length of the image, s is the object distance, and s' is the image distance.

[0065] The phase shift characteristics of the fundamental mode Gaussian beam are determined by the phase factor It describes the phase lag of a Gaussian beam at (x, y, z) relative to the origin (0, 0, 0). Where kz describes the geometric phase shift; The factor describes the additional phase advance of the Gaussian beam relative to the geometric phase shift when it travels a distance z in space; represents the phase shift related to the abscissa (x, y), which shows that the equiphase surface of the Gaussian beam is a sphere with radius R, where R is given by the following formula:

[0066] ;

[0067] In addition, the imaging formula of a thin lens in geometric optics is:

[0068]

[0069] This formula also applies to Gaussian beams. After a Gaussian beam passes through an ideal lens without aberration, it is still a Gaussian beam. As shown in the figure: the beam radius is the smallest at the beam waist. The farther away from the beam waist, the larger the beam radius. The incident Gaussian beam and the outgoing Gaussian beam passing through the lens group have their own beam waist and divergence angle. The input beam waist radius ω 0 As the object height, the output beam waist radius ω 0 'As the image height, the improved thin lens formula for calculating Gaussian propagation is:

[0070]

[0071]

[0072] Among them, Z R is the Rayleigh distance of the input beam, which refers to the distance from the beam waist radius to It is generally believed that the fundamental mode Gaussian beam is approximately parallel within the Rayleigh length range.

[0073] From the formula, we can see that when (πω 0 2 / λ) 2 <<(sf) 2When (that is, the distance between the waist of the Gaussian beam and the rear focal plane of the lens is much larger than the Rayleigh distance of the object Gaussian beam), the formula for the Gaussian beam passing through a thin lens is consistent with the formula for an ideal thin lens. The method for processing paraxial rays in geometric optics can be used to process Gaussian beams. However, in practical applications, the waist of the Gaussian beam is often not far enough from the lens, so the characteristics of Gaussian beam propagation still need to be considered. The propagation mode of the Gaussian beam through a thin lens is different from the results of geometric optics, which is reflected in:

[0074] When the condition that the waist of the Gaussian beam is far enough from the lens is not met, compared with the focus position of geometric optics, no matter whether the waist of the incident Gaussian beam is located on the left or right side of the front focal plane of the thin lens, the focal plane (waist plane) of the Gaussian beam transmitted by the lens is always closer to the thin lens than the focus position of geometric optics (i.e., the focus displacement of the focused Gaussian beam), which can be expressed by the formula: Δf′=f′[1+(πω 2 / λf′) 2 ]The displacement of the Gaussian beam can be calculated.

[0075] In the self-reference alignment system of the lithography machine, the illumination objective lens and the diffraction objective lens are designed to form a 4f optical structure for alignment imaging. The illumination unit uses a wide-band laser beam with a wavelength ranging from 520nm to 852nm. The beam waist of the laser beam is placed at the front focal plane of the illumination objective lens (which is also the front focal plane of the entire 4f optical structure). The wide-band laser is collimated by a telephoto illumination lens group, and the beam waist is roughly located at the back focal plane of the illumination objective lens. At the same time, the air gap between the illumination objective lens and the diffraction objective lens is adjusted so that when the beam waist of the back focal plane of the diffraction objective lens is transmitted to the silicon wafer surface through the diffraction objective lens, the wavefront phase shift of the beam waist of Gaussian beams of different wavelengths reaching the image plane is minimized.

[0076] For the latter part of the 4f optical system - the diffraction objective lens, the laser beam collimated by the telephoto illumination lens group enters the diffraction objective lens, with a wavelength range of 520nm to 852nm. However, the general achromatic lens group can only correct the positional chromatic aberration of two colors of light, and their common image point is still offset relative to the image point of the third wavelength - the dipole spectrum. The general idea of ​​eliminating the dipole spectrum includes two points: (1) Select three types of glass as the initial glass in the P-υ diagram. The glass far away from the ordinary glass curve of the P-υ diagram is a special glass with a better achromatic effect. The larger the area enclosed by the glass, the better; (2) According to the achromatic and apochromatic formulas, for the lens group with a positive total focal length, the positive lens uses a glass with a low refractive index and a high Abbe number, and the negative lens uses a glass with a high refractive index and a low Abbe number.

[0077] Based on the above analysis, the present invention provides a sample measurement system, which, through a 4f optical system composed of a telephoto illumination lens group and a plan-apochromatic diffraction objective, can make Gaussian beams of different wavelengths meet the wavefront aberration requirements of the measurement system, while reducing the longitudinal focal shift, improving the alignment accuracy and reducing odd-order wave aberrations.

[0078] The sample measurement system comprises:

[0079] A lighting unit, used for providing a broadband light source;

[0080] Telephoto illumination lens set, used for collimating wide-band light sources or reducing wavefront phase differences of different wavelengths;

[0081] A plan apochromatic diffraction objective lens is used to reduce longitudinal focal shift or odd-order wave aberration for a wide-band light source passing through the telephoto illumination lens assembly;

[0082] A detection unit, detecting an image formed on the sample by the wide-band light source passing through the plan apochromatic diffraction objective lens to obtain a light signal;

[0083] The information processing unit processes the obtained optical signal to obtain a processing result.

[0084] The sample is preferably a silicon wafer and a substrate, but is not limited thereto. An alignment mark may be provided on the sample, and the alignment mark may be a scribe groove alignment mark.

[0085] The broadband light source provided by the illumination unit is preferably a broadband laser beam. Therefore, the illumination unit can use KrF excimer laser, ArF excimer laser, F2 laser, Kr2 laser, Ar2 laser, or use ultra-high pressure mercury lamp (g-line, i-line) and the like.

[0086] Figure 1 A schematic diagram of the structure of a telephoto illumination lens assembly and a plan-apochromatic diffraction objective lens assembly is shown; Figure 2 A schematic structural diagram of the telephoto lighting lens assembly is shown. Figure 2 After the wide-band light source passes through the telephoto illumination lens group, it enters the ideal lens, and the ideal lens group is an ideal lens without aberration, and the ideal lens group is common knowledge, which will not be described here. The role of the ideal lens group here is only to simply and clearly highlight the effect of the telephoto illumination lens group, and it cannot replace the plan apochromatic diffraction objective lens.

[0087] The telephoto lighting lens assembly includes, in order from the object plane side along the optical axis: a first double cemented lens 101 with negative optical power, a first meniscus negative lens 102, a first negative lens 103 and a first biconvex positive lens 104.

[0088] The first double-cemented lens 101 is formed by cementing a positive lens and a negative lens. The first double-cemented lens 101 has negative optical power, and the materials of the two lenses in the first double-cemented lens 101 are preferably N-SK10 and S-BLS7, but are not limited thereto.

[0089] The material of the first meniscus negative lens 102 is preferably S-BLS7, but not limited thereto; the first negative lens 103 is preferably a plano-concave lens, and its material is preferably SF56A, but not limited thereto; the material of the first biconvex positive lens 104 is preferably N-PK51, but not limited thereto.

[0090] The focal length of each component in the telephoto lighting lens assembly and the total focal length satisfy the following relationship:

[0091] -1.3 <f 1 / f<-0.6;

[0092] -1.9 <f 2 / f<-1.3;

[0093] -1.6 <f 3 / f<-1;

[0094] 0.1 <f 4 / f<0.6.

[0095] Among them, f 1 is the focal length of the first double cemented lens 101, f 2 is the focal length of the first meniscus negative lens 102, f 3 is the focal length of the first negative lens 103, f 4 is the focal length of the first biconvex positive lens 104, and f is the total focal length of the telephoto lighting lens assembly.

[0096] In this embodiment, the broadband light source is preferably a broadband laser beam. A light-cutting diaphragm is provided on one side of the object plane of the telephoto illumination lens assembly, and the light-cutting diaphragm is specifically placed in front of the first double-cemented lens 101, for example, the light-cutting diaphragm is placed 78.52 mm in front of the first double-cemented lens 101, and the beam waist position of the laser beam coincides with the position of the light-cutting diaphragm.

[0097] The lens material, thickness and space interval between lenses of each component in the telephoto lighting lens assembly only need to satisfy the relationship between the focal length of each component and the total focal length of the telephoto lighting lens assembly. Therefore, the material, thickness and space interval between lenses of each component can be selected according to the relationship between the focal length of each component and the total focal length of the telephoto lighting lens assembly. For example, Table 1 shows the material, thickness and space interval between lenses of each component. 11 ,d13 ,d 15 ,d 17 ,d 19 are the thickness of the lens of each component starting from the object plane side, d 0 ,d 12 ,d 14 ,d 16 ,d 18 The front and back and radius values ​​of the position represent the front and back curvature radii of the lens and the back curvature radii of the lens.

[0098] Table 1:

[0099]

[0100]

[0101] When the telephoto illumination lens group plus the ideal lens are used for imaging, the operand of the Gaussian beam is used to read the curvature radius of the Gaussian beam waist with different wavelengths reaching the image plane, and the values ​​are all above the meter level. According to the above known knowledge, it can be calculated that the phase deviation of the Gaussian beam waist with the main wavelength of 633nm reaching the image plane is 0.155nm, which meets the requirement of the self-reference alignment system that the wavefront aberration is less than λ / 100.

[0102] See also Figure 3 The plan apochromatic diffraction objective lens group includes, from one side of the object plane along the optical axis, the following:

[0103] A first lens element group 201 is formed to correct field-dependent aberrations;

[0104] The second lens element group 202 is composed to correct the high-order chromatic spherical aberration;

[0105] The third lens element group 203 is composed to correct low-order chromatic spherical aberration;

[0106] The fourth lens element group 204 forms a positive focal power group that meets the requirements of large numerical aperture and long working distance.

[0107] The focal length of each component in the plan apochromatic diffraction objective lens group and the total focal length satisfy the following relationship:

[0108] 8 <f 1 ' / f'<12;

[0109] 3 <f 2 ' / f'<5;

[0110] -3 <f 3 ' / f'<-2;

[0111] 0.4 <f 4 ' / f'<1.5.

[0112] Among them, f 1 ' is the focal length of the first lens element group 201, f 2 ' is the focal length of the second lens element group 202, f 3 ' is the focal length of the third lens element group 203, f 4 ' is the focal length of the fourth lens element group 204, and f' is the total focal length of the plan apochromatic diffractive objective lens group.

[0113] The working band of the plan apochromatic diffraction objective lens set is 520nm~852nm, and the NA is calculated by Zemax software to be > 0.6, the longitudinal focal shift LFS = 0.09um, the RMS wavefront aberration = 0.01wv, the odd-order wavefront aberration PV value = 0.026wv, the working distance is greater than 6.3mm, and the main ray angle is less than 0.006°, which meets the image telecentricity requirement. Compared with the prior art, the longitudinal focal shift LFS is reduced by half, which can be seen in Figure 4 .

[0114] See also Figure 3 In this embodiment, the first lens element group 201 includes a second meniscus negative lens and a second biconvex positive lens matched therewith, which together form a structure for eliminating field-dependent aberrations. The first lens element group 201 has a positive focal length as a whole, which makes the light converge slowly, while the first lens group in the prior art mainly makes the light diverge.

[0115] The second lens element group 202 includes two double-cemented lenses, namely a second double-cemented lens and a third double-cemented lens. The two double-cemented lenses are both a combination of low-dispersion material and ultra-high-dispersion material, and are double-cemented lenses with weak positive focal length. The positive lenses in the two double-cemented lenses are preferably ultra-high-dispersion materials, such as S-FPL53, but not limited thereto; the negative lens materials in the two double-cemented lenses are preferably normal-dispersion materials. The second lens element group 202 is mainly used to correct high-order spherical aberration.

[0116] The third lens element group 203 is a double-cemented lens behind the aperture 5, that is, the fourth double-cemented lens. The fourth double-cemented lens has a negative optical focal length as a whole, and the positive lens in the fourth double-cemented lens adopts a material with a low refractive index and a high dispersion coefficient, such as S-FPL53, but not limited thereto. The negative lens in the fourth double-cemented lens adopts a material with a high refractive index and a low dispersion coefficient, such as S-TIH1, but not limited thereto. The third lens element group 203 is mainly used to correct the low-order spherical aberration brought by the fourth lens element group 204 and balance the overall positive optical focal length of the fourth lens element group 204. And the second lens element group 202 and the third lens element group 203 constitute an apochromatic system as a whole, which is used to eliminate the secondary spectrum brought by the wide band.

[0117] The fourth lens element group 204 includes three lenses with positive focal power, i.e., three positive lenses, which include: a first positive lens, a second positive lens, and a third positive lens in order from the object plane side along the optical axis. The fourth lens element group 204 is mainly used to focus the light, ensuring that the NA is greater than 0.6, the working distance is greater than 6.3 mm, and the main light angle is less than 0.006°. The last lens in the fourth lens element group 204 close to the silicon wafer surface is a Qiming meniscus lens, which can ensure that the spherical aberration coma at the Qiming point is 0, and the first negative lens (i.e., the second meniscus negative lens) in the first lens element group 201 plus the air space in the middle cooperates with the last meniscus lens to jointly eliminate the field-dependent aberration in the system, and the glass materials of the three positive lenses of the fourth lens element group 204 are all ultra-low dispersion materials, meeting the requirements of system achromatism.

[0118] The lens material, thickness and space interval between lenses of each component in the plan apochromatic diffractive objective lens only need to satisfy the relationship between the focal length of each component and the total focal length in the plan apochromatic diffractive objective lens. Therefore, the material, thickness and space interval between lenses of each component can be selected according to the relationship between the focal length of each component and the total focal length in the plan apochromatic diffractive objective lens. For example, Table 2 shows the material, thickness and space interval between lenses of each component.

[0119] Table 2:

[0120]

[0121]

[0122] The overall focal length of the plan apochromatic diffraction objective in this embodiment is distributed as positive, positive, negative, positive, which is very different from the overall negative, negative, positive, negative, positive structure of the prior art. In addition, among the available achromatic glasses, OHARA's S-FPL53 glass is selected as the special glass with ultra-low dispersion, which avoids the conventional selection of CaF 2 glass, while CaF 2 Glass is soft, difficult to process, and has poor resistance to deliquescence, acid and alkali. This embodiment uses 11 pieces of glass as a whole, and there is no element specifically used to correct the coma caused by centrifugation. Instead, the overall structure is matched to distribute and balance the coma.

[0123] In the present embodiment, the telephoto illumination lens group and the plan apochromatic diffraction objective lens group as a whole form a 4f optical system. Due to the difference in geometric optics and Gaussian beam propagation during use, it is necessary to adjust the air gap between the telephoto illumination lens group and the plan apochromatic diffraction objective lens group so that the curvature radius of Gaussian beams of different wavelengths reaching the image plane is maximized and the wavefront phase deviation is minimized. In the use scenario of image-side afocality (i.e., parallel light in and parallel light out), the optical path difference of the entire 4f optical system reaching the silicon wafer surface is 0.0005wv.

[0124] The present invention also provides another plan apochromatic diffractive objective lens, i.e., the second embodiment, and the difference between this embodiment and the previous embodiment is that the relationship between the focal length of each component in the plan apochromatic diffractive objective lens group and the total focal length is different, so the materials, thicknesses and space intervals between lenses of each component in the plan apochromatic diffractive objective lens group selected according to the relationship between the focal length of each component and the total focal length will also be different. However, the overall functions of each component are the same.

[0125] Figure 5 A schematic structural diagram of another telephoto illumination lens assembly and a plan-apochromatic diffraction objective lens assembly (ie, the second embodiment) is shown.

[0126] Telephoto illumination lens set, used for collimating wide-band light sources or reducing wavefront phase differences of different wavelengths;

[0127] The plan apochromatic diffractive objective lens reduces the longitudinal focal shift or odd-order wave aberration of the wide-band light source passing through the telephoto illumination lens group, and the plan apochromatic diffractive objective lens has a lens group with positive, positive, negative and positive optical powers respectively.

[0128] Figure 6 The schematic diagram of the structure of the telephoto lighting lens assembly of the second embodiment is shown. The telephoto lighting lens assembly of the second embodiment is the same as the first embodiment. Figure 6 After the wide-band light source passes through the telephoto lighting lens group, it enters the ideal lens group, which is an ideal lens without aberration, and the ideal lens group is common knowledge, which will not be described here. The role of the ideal lens group here is only to simply and clearly highlight the effect of the telephoto lighting lens group, and it is not the technical solution of this embodiment.

[0129] The telephoto lighting lens assembly includes, in order from the object plane side along the optical axis: a first double cemented lens 111 with negative optical power, a first meniscus negative lens 112, a first negative lens 113 and a first double convex positive lens 114.

[0130] The first double-cemented lens 111 is formed by cementing a positive lens and a negative lens. The first double-cemented lens 111 has negative optical power, and the materials of the two lenses in the first double-cemented lens 111 are preferably S-FPL51 and S-BLS7, but are not limited thereto.

[0131] The material of the first meniscus negative lens 112 is preferably S-BLS7, but not limited thereto; the first negative lens 113 is preferably a plano-concave lens, and its material is preferably SF6, but not limited thereto; the material of the first biconvex positive lens 114 is preferably S-FPL51, but not limited thereto.

[0132] The focal length of each component in the telephoto lighting lens assembly and the total focal length satisfy the following relationship:

[0133] -1 <f 1 / f<-0.1;

[0134] -1.1 <f 2 / f<-0.2;

[0135] -5 <f 3 / f<-3.5;

[0136] 0 <f 4 / f<0.7.

[0137] Among them, f 1 is the focal length of the first double cemented lens 111, f 2 is the focal length of the first meniscus negative lens 112, f 3 is the focal length of the first negative lens 113, f 4 is the focal length of the first biconvex positive lens 114, and f is the total focal length of the telephoto lighting lens assembly.

[0138] In this embodiment, the broadband light source is preferably a broadband laser beam. A light-cutting diaphragm is provided on one side of the object plane of the telephoto illumination lens assembly, and specifically, the light-cutting diaphragm is placed in front of the first double-cemented lens 111, and the beam waist position of the laser beam coincides with the position of the light-cutting diaphragm.

[0139] The lens material, thickness and space interval between lenses of each component in the telephoto lighting lens assembly only need to satisfy the relationship between the focal length of each component and the total focal length of the telephoto lighting lens assembly. Therefore, the material, thickness and space interval between lenses of each component can be selected according to the relationship between the focal length of each component and the total focal length of the telephoto lighting lens assembly. For example, Table 3 shows the material, thickness and space interval between lenses of each component. 31 ,d 33 ,d 35 ,d 37,d 39 are the thickness of the lens of each component starting from the object plane side, d 0 ,d 32 ,d 34 ,d 36 ,d 38 are the object distance or the spatial interval between lenses, respectively.

[0140] Table 3:

[0141]

[0142] See also Figure 7 A schematic structural diagram of the plan apochromatic diffraction objective lens assembly of the second embodiment is shown.

[0143] The plan apochromatic diffraction objective lens assembly includes, from the object plane side along the optical axis, the following:

[0144] A first lens element group 211 is formed to correct field-dependent aberrations;

[0145] The second lens element group 212 is composed to correct the high-order chromatic spherical aberration;

[0146] The third lens element group 213 is composed to correct low-order chromatic spherical aberration;

[0147] The fourth lens element group 214 forms a positive focal power group that meets the requirements of large numerical aperture and long working distance.

[0148] The focal length of each component in the plan apochromatic diffraction objective lens group and the total focal length satisfy the following relationship:

[0149] 5 <f 1 ' / f'<10;

[0150] 5 <f 2 ' / f'<8;

[0151] -2.6 <f 3 ' / f'<-1.6;

[0152] 0.4 <f 4 ' / f'<1.4.

[0153] Among them, f1' is the focal length of the first lens element group 211, f2' is the focal length of the second lens element group 212, f3' is the focal length of the third lens element group 213, f4' is the focal length of the fourth lens element group 214, and f' is the total focal length of the plan apochromatic diffractive objective lens group.

[0154] See also Figure 7In this embodiment, the first lens element group 211 includes a second meniscus negative lens and a second biconvex positive lens matched therewith, which together form a structure for eliminating field-dependent aberrations. The first lens element group 211 has a positive focal power as a whole, which makes the light converge slowly, while the first lens group in the prior art mainly makes the light diverge.

[0155] The second lens element group 212 includes a negative lens and a double cemented lens, that is, a second negative lens and a second double cemented lens. The second double cemented lens is a combination of low dispersion material and ultra-high dispersion material, and is a double cemented lens with weak positive focal length. The positive lenses in the second double cemented lens are preferably ultra-high dispersion materials, such as S-FPL53, but not limited thereto; the negative lens materials in the second double cemented lens are preferably normal dispersion materials. The second lens element group 212 is mainly used to correct high-order spherical aberration.

[0156] The third lens element group 213 is a double-cemented lens behind the aperture 5, that is, the third double-cemented lens. The third double-cemented lens has a negative optical focal length as a whole, and the positive lens in the third double-cemented lens adopts a material with a low refractive index and a high dispersion coefficient, such as S-FPL53, but not limited thereto. The negative lens in the third double-cemented lens adopts a material with a high refractive index and a low dispersion coefficient, such as N-KZFS11, but not limited thereto. The third lens element group 213 is mainly used to correct the low-order spherical aberration brought by the fourth lens element group 214 and balance the overall positive optical focal length of the fourth lens element group 214. The second lens element group 212 and the third lens element group 213 constitute an apochromatic system as a whole, which is used to eliminate the secondary spectrum brought by the wide band.

[0157] The fourth lens element group 214 includes four lenses with positive focal power, that is, four positive lenses, which include: a first positive lens, a second positive lens, a third positive lens and a fourth positive lens in order from the object plane side along the optical axis. The fourth lens element group 214 is mainly used to focus the light, ensuring that the NA is greater than 0.6, the working distance is greater than 6.3mm, and the main light angle is less than 0.006°. The last lens in the fourth lens element group 214 close to the silicon wafer surface is a Qiming meniscus lens, which can ensure that the spherical aberration coma at the Qiming point is 0, and the first negative lens (that is, the second meniscus negative lens) in the first lens element group 211 plus the air space in the middle cooperates with the last meniscus lens to jointly eliminate the field-dependent aberration in the system, and the glass materials of the four positive lenses of the fourth lens element group 214 are all ultra-low dispersion materials, meeting the requirements of system achromatism.

[0158] The lens material, thickness and space interval between lenses of each component in the plan apochromatic diffractive objective lens only need to satisfy the relationship between the focal length of each component and the total focal length in the plan apochromatic diffractive objective lens. Therefore, the material, thickness and space interval between lenses of each component can be selected according to the relationship between the focal length of each component and the total focal length in the plan apochromatic diffractive objective lens. For example, Table 4 shows the material, thickness and space interval between lenses of each component.

[0159] Table 4:

[0160]

[0161]

[0162] The working band of the plan apochromatic diffraction objective lens set is 520nm~852nm, NA>0.6, longitudinal focal shift LFS=0.1μm, RMS wavefront aberration=0.03wv, odd-order wavefront aberration PV value=0.0167wv, working distance is greater than 6.3mm, and the main ray angle is less than 0.006°, which meets the image telecentricity requirement. Compared with patent CN 108292038B, the longitudinal focal shift LFS is reduced by half. Figure 8 shown.

[0163] The detection unit of the present invention is used to detect the image formed by the wide-band light source passing through the plan apochromatic diffraction objective on the sample to obtain a light signal. The detection unit includes a detection optical path and a detector, and the detection optical path transmits the light signal obtained by detecting the image formed on the sample to the detector. The detector is preferably a CCD detector. Since the detection unit is a well-known technology, it will not be described in detail here.

[0164] The information processing module of the present invention processes the optical signal obtained by the detection unit, and determines the position information of the alignment mark according to the phase information of the optical signal.

[0165] In addition, the present invention further provides a lithography device, and the lithography device includes the sample measurement system described above.

[0166] In the prior art, in the sample measurement system of the lithography equipment, the wide-band 4f optical system based on laser transmission has large chromatic aberration on the silicon wafer surface. In addition, since five wavelengths are involved, the general achromatic system can only correct two colors of light and cannot eliminate the secondary spectrum. The present invention can eliminate the secondary spectrum caused by the five wavelengths, reduce the longitudinal focal shift of the image plane from 10 microns to 0.1 microns, reduce the RMS wave aberration from 0.5wv to 0.01wv, and reduce the odd-order wave aberration PV value from 0.332wv to 0.026wv. Therefore, the sample measurement system of the present invention can first reduce the influence of chromatic aberration and then improve the alignment accuracy of the lithography equipment.

[0167] Moreover, in the prior art, in the sample measurement system of the lithography equipment, the system based on laser transmission needs to consider the difference between geometric optics and physical optics, and needs to solve the position offset of Gaussian beam waists of different wavelengths reaching the image plane through the lens group. However, the present invention can control the position offset of different wavelengths reaching the image plane relative to the geometric focus through the air gap, and at the same time can control the curvature radius of the wavefront of the Gaussian beam reaching the silicon wafer surface to more than the meter level, so that the wavefront phase deviation of each wavelength reaching the phase plane is less than λ / 100. Therefore, the sample measurement system of the present invention can first reduce the wave aberration of different wavelengths reaching the sample (silicon wafer surface), and then improve the alignment accuracy of the lithography equipment (self-reference solution).

[0168] In summary, it can be seen that the telephoto illumination lens group and the plan-apochromatic diffraction objective lens in the lithography equipment and sample measurement system provided by the present invention can meet other working requirements while the Gaussian beams of different wavelengths meet the wavefront aberration requirements of the measurement system, and the longitudinal focal shift is reduced by half. In addition, the chromatic aberration can be reduced first, and then the alignment accuracy of the sample measurement system can be improved, and the use of CaF2 glass can be avoided.

[0169] In addition, it is understood that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

[0170] It should also be understood that the present invention is not limited to the specific methods, compounds, materials, manufacturing techniques, usages and applications described herein, which may vary. It should also be understood that the terms described herein are only used to describe specific embodiments, rather than to limit the scope of the present invention. It must be noted that the singular forms "one", "a kind" and "the" used herein and in the appended claims include plural references unless the context clearly indicates the opposite meaning. Thus, for example, a reference to "a step" means a reference to one or more steps, and may include secondary steps. All conjunctions used should be understood in the broadest sense. Therefore, the word "or" should be understood to have the definition of a logical "or", rather than a logical "exclusive or", unless the context clearly indicates the opposite meaning. The structure described herein will be understood to also quote the functional equivalent of the structure. Language that can be interpreted as approximate should be understood as such, unless the context clearly indicates the opposite meaning.

Claims

1. A sample measurement system, characterized in that: include: A lighting unit, used for providing a broadband light source; Telephoto illumination lens set, used for collimating wide-band light sources or reducing wavefront phase differences of different wavelengths; A plan apochromatic diffraction objective lens is used to reduce longitudinal focal shift or odd-order wave aberration for a wide-band light source passing through the telephoto illumination lens assembly; A detection unit, detecting an image formed on the sample by the wide-band light source passing through the plan apochromatic diffraction objective lens to obtain a light signal; The information processing unit processes the obtained optical signal to obtain a processing result.

2. The sample measurement system according to claim 1, characterized in that: The telephoto lighting lens assembly comprises, in order from one side of the object plane along the optical axis: a first double cemented lens with negative optical power, a first meniscus negative lens, a first negative lens and a first double convex positive lens.

3. The sample measurement system according to claim 2, characterized in that: The plan apochromatic diffraction objective lens has a lens group with positive, positive, negative and positive optical powers respectively.

4. The sample measurement system according to claim 3, characterized in that: The plan apochromatic diffraction objective lens comprises, in order from one side of the object plane along the optical axis: A first lens element group, composed to correct field-dependent aberrations; The second lens element group is composed of corrected high-order chromatic spherical aberrations; The third lens element group is composed of corrected low-order chromatic spherical aberrations; The fourth lens element group forms a positive focal power group that meets the requirements of large numerical aperture and long working distance.

5. The sample measurement system according to claim 4, characterized in that: The relationship between the focal length of each lens in the telephoto lighting lens assembly and the total focal length is: -1.3 <f1 / f<-0.6; -1.9 <f2 / f<-1.3; -1.6 <f3 / f<-1; 0.1 <f4 / f<0.6; Wherein f1 is the focal length of the first double cemented lens, f2 is the focal length of the first meniscus negative lens, f3 is the focal length of the first negative lens, f4 is the focal length of the first double convex positive lens, and f is the total focal length of the telephoto lighting lens assembly.

6. The sample measurement system according to claim 5, characterized in that: The first lens element group includes, in sequence from the object plane side along the optical axis, a second meniscus negative lens and a second double convex positive lens matched therewith; the second lens element group includes a second double cemented lens and a third double cemented lens, both of which are combinations of low-dispersion material and ultra-high-dispersion material, and are both cemented lenses with weak positive optical power; the third lens element group includes a fourth double cemented lens, and the fourth double cemented lens has negative optical power as a whole; the fourth lens element group includes three lenses with positive optical power, and the three lenses with positive optical power are made of low-dispersion material.

7. The sample measurement system according to claim 5, characterized in that: The relationship between the focal length of each lens in the plan apochromatic diffraction objective and the total focal length is: 8 <f1’ / f’<12; 3 <f2’ / f’<5; -3 <f3’ / f’<-2; 0.4 <f4’ / f’<1.5; Where f1' is the focal length of the first lens element group, f2' is the focal length of the second lens element group, f3' is the focal length of the third lens element group, f4' is the focal length of the fourth lens element group, and f' is the total focal length of the plan apochromatic diffractive objective lens.

8. The sample measurement system according to claim 4, characterized in that: The relationship between the focal length of the lens in the telephoto lighting lens assembly and the total focal length is: -1 <f1 / f<-0.1; -1.1 <f2 / f<-0.2; -5 <f3 / f<-3.5; 0 <f4 / f<0.7; Among them, f1 is the focal length of the first cemented lens, f2 is the focal length of the first meniscus negative lens, f3 is the focal length of the first negative lens, f4 is the focal length of the first double convex positive lens, and f is the total focal length of the telephoto lighting lens assembly.

9. The sample measurement system according to claim 8, characterized in that: The first lens element group includes, from the object plane side, a second meniscus negative lens and a second biconvex positive lens matched therewith; the second lens element group includes a second double cemented lens and a positive lens; the third lens element group includes a third double cemented lens, and the third double cemented lens has a negative optical power as a whole; the fourth lens element group includes three positive lenses.

10. The sample measurement system according to claim 8, characterized in that: The relationship between the focal length of the lens in the plan apochromat objective and the total focal length is: 5 <f1’ / f’<10; 5 <f2’ / f’<8; -2.6 <f3’ / f’<-1.6; 0.4 <f4’ / f’<1.4; Where f1' is the focal length of the first lens element group, f2' is the focal length of the second lens element group, f3' is the focal length of the third lens element group, f4' is the focal length of the fourth lens element group, and f' is the total focal length of the plan apochromatic diffractive objective lens.

11. The sample measurement system according to claim 1, wherein: The broadband light source is a laser beam.

12. The sample measurement system according to claim 11, wherein: A light-cutting diaphragm is arranged on one side of the object plane of the telephoto illumination objective lens, and the position of the light-cutting diaphragm coincides with the beam waist position of the laser beam.

13. A lithography apparatus, characterized in that: The method comprises the sample measurement system according to any one of claims 1 to 12.

Images