Deep ultraviolet objective lens optical system, deep ultraviolet objective lens, and wafer inspection microscope.

Abstract

It guarantees the accuracy of the image formation. [Solution] An embodiment of the deep ultraviolet objective lens optical system includes a first lens group, a second lens group, and a third lens group arranged sequentially along the same optical axis from the image side to the object side. The refractive powers of the first and third lens groups are positive, the refractive power of the first lens group is smaller than that of the third lens group, and the refractive power of the second lens group is negative. The third lens group has a greater refractive power than the first lens group and is responsible for collecting the scattered energy of light rays from the defect location of the object, collecting the scattered energy of light rays from the defect location of the object at a short distance. The second lens group has a negative refractive power and can compensate for angular differences at each position to achieve flat-field correction. The first lens group has a relatively weak positive refractive power and can compensate for higher-order aberrations. The combination of these three specific lens groups can effectively guarantee the accuracy of imaging.

Description

Technical Field

[0001] The present invention relates to the technical field of optical devices, and particularly to a deep ultraviolet objective lens optical system, a deep ultraviolet objective lens, and a microscope for wafer inspection.

Background Art

[0002] With the rapid development of the country's semiconductor chip field, it is inevitable to replace the import of wafer inspection-related equipment. The inspection equipment for surface particles of a wafer is mainly used for identifying and locating problems such as impurity particle contamination, mechanical scratches, and wafer pattern defects existing on the product surface. Wafer defects may cause leakage or disconnection during the use of semiconductor products, affecting the yield of chips. Therefore, in order to improve the chip yield, it is necessary to inspect wafer defects. Before performing wafer defect inspection, it is necessary to collect the light scattering energy from the wafer defect position, and the deep ultraviolet objective lens is responsible for this function. However, since the deep ultraviolet objective lens has a great influence on the accuracy of imaging, how to provide a deep ultraviolet objective lens optical system that guarantees the accuracy of imaging is an issue to be solved.

Summary of the Invention

Problems to be Solved by the Invention

[0003] The present invention provides a deep ultraviolet objective lens optical system, a deep ultraviolet objective lens, and a microscope for wafer inspection in order to guarantee the accuracy of imaging.

Means for Solving the Problems

[0004] The present invention provides the following solutions. According to a first aspect, a deep ultraviolet objective lens optical system is provided. The optical system includes a first lens group, a second lens group, and a third lens group that are sequentially arranged along the same optical axis from the image side to the object side. Among them, the refractive powers of the first lens group and the third lens group are both positive, and the refractive power of the first lens group is smaller than the refractive power of the third lens group. The refractive power of the second lens group is negative.

[0005] According to one possible embodiment of the present invention, the first lens group includes, in order along the same optical axis from the image side to the object side, a first lens having positive refractive power, a second lens having positive refractive power, a third lens having negative refractive power, and a fourth lens having negative refractive power, and / or, the second lens group includes, in order along the same optical axis from the image side to the object side, a fifth lens having positive refractive power and a sixth lens having positive refractive power, and / or, the third lens group includes, in order along the same optical axis from the image side to the object side, a seventh lens having negative refractive power, an eighth lens having positive refractive power, a ninth lens having positive refractive power, and a tenth lens having positive refractive power.

[0006] According to one possible embodiment of the present invention, the first, fifth, sixth, ninth, and tenth lenses are all positive meniscus lenses, with the convex surface of the positive meniscus lens facing the image side; the second and eighth lenses are both biconvex lenses; the third and fourth lenses are both negative meniscus lenses, with the concave surface of the negative meniscus lens facing the image side; and the seventh lens is a biconcave lens. According to one possible embodiment of the present invention, the optical system further includes an aperture diaphragm, the aperture diaphragm located on the image side of the first lens group.

[0007] According to one possible embodiment of the present invention, the first lens group, the second lens group, and the third lens group all use fused silica lenses of the deep ultraviolet spectral segment.

[0008] According to one possible embodiment of the present invention, the numerical aperture (NA) on the object side of the deep ultraviolet objective lens is greater than 0.95, the focal length of the deep ultraviolet objective lens is 50 mm, the total length of the optical system is less than 200 mm, and the field of view radius on the object side is 0.19 mm or less.

[0009] According to one possible embodiment of the present invention, parallel light is emitted from the image side of the optical system, and the apertures of the lenses included in the first lens group, the second lens group, and the third lens group are all 100.5 mm or less.

[0010] According to one possible embodiment of the present invention, the focal length of the first lens group is 260 mm to 280 mm, the focal length of the second lens group is -275 mm to -220 mm, and the focal length of the third lens group is 20 mm to 25 mm.

[0011] According to a second aspect, a deep ultraviolet objective lens is provided, the deep ultraviolet objective lens comprising an optical system according to the first aspect.

[0012] According to a third aspect, a wafer inspection microscope is provided, the wafer inspection microscope includes a deep ultraviolet objective lens according to a second aspect, and the deep ultraviolet objective lens includes an optical system according to a first aspect. [Effects of the Invention]

[0013] Through specific embodiments of the present invention, the present invention discloses the following technical effects. 1) In this invention, the third lens group has a greater refractive power than the first lens group and is responsible for collecting light ray scattering energy from the object defect location, collecting light ray scattering energy from the object defect location at a short distance. The second lens group has a negative refractive power and can effectively compensate for angular differences at each position to achieve flat-field correction. The first lens group has a relatively weak positive refractive power and can compensate for higher-order aberrations. The combination of these three specific lens groups can effectively guarantee the accuracy of imaging. 2) All lenses in this invention employ a spherical design to avoid manufacturing difficulties caused by the introduction of aspherical or free-form surfaces. 3) The first, second, and third lens groups in this invention all employ fused silica lenses of the same type in the deep ultraviolet spectral segment, providing good thermal stability and ultra-high transmittance in the deep ultraviolet spectral segment. 4) In the present invention, the object-side field of view radius is 0.19 mm or less, meaning the entire field of view is 0.38 mm or less. On the other hand, the field of view of a conventional objective lens with an object-side numerical aperture (NA) of 0.9 is typically 0.1 mm. Therefore, the entire field of view according to the present invention is approximately four times that of a typical field of view, providing a large field of view characteristic, and the overall length is also optimized. 5) The object-side numerical aperture (NA) of the deep ultraviolet objective lens in this invention is greater than 0.95, the operating wavelength is 266 nm, and the bandwidth is 1 nm. Therefore, the optical system possesses both a large numerical aperture and high resolution characteristics.

[0014] Naturally, any product into which the present invention is implemented does not necessarily have to achieve all of the advantages described above simultaneously. [Brief explanation of the drawing]

[0015] To more clearly explain embodiments of the present invention or prior art, the following briefly introduces the drawings necessary for describing the embodiments. Clearly, the drawings described below represent only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these without any creative effort. [Figure 1] This is a deep ultraviolet objective lens optical system according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of the optical path of a deep ultraviolet objective lens optical system according to an embodiment of the present invention. [Figure 3] This is a diagram of the imaging spot of the deep ultraviolet objective lens optical system according to an embodiment of the present invention. [Figure 4] This is a schematic diagram illustrating the imaging energy concentration of a deep ultraviolet objective lens optical system according to an embodiment of the present invention. [Figure 5] This is a schematic diagram of the imaging telecentricity of a deep ultraviolet objective lens optical system according to an embodiment of the present invention.

Best Mode for Carrying Out the Invention

[0016] Hereinafter, while referring to the drawings of the embodiments of the present invention, the technical solutions according to the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention.

[0017] The terms used in the embodiments of the present invention are only for explaining specific embodiments and are not for limiting the present invention. The singular forms "a kind of", "the above-mentioned", and "the said" used in the embodiments of the present invention and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0018] In addition, the term "and / or" used in this specification simply represents the relationship of the related objects and indicates that three relationships can exist. For example, A and / or B can represent three situations: only A exists, A and B exist simultaneously, and only B exists. Also, the symbol " / " in this specification generally indicates that the related objects before and after are in an "or" relationship.

[0019] The orientation or positional relationship such as "above", "below", "front", "rear", "left", "right", etc. used in the embodiments of the present invention is only for facilitating the description of the present invention and does not limit that the devices or components according to the present invention must have a specific orientation or position. It should be understood that all these descriptions of orientation or positional relationship are relative. Any changes, equivalent substitutions, improvements, etc. made within the scope of the idea of the present invention should all be included in the protection scope of the present invention.

[0020] Currently, by monitoring the manufacturing process through wafer defect detection, the yield loss can be reduced and the process yield can be improved. Among all semiconductor inspection devices, a large number of devices apply optical detection technology, covering all advanced processes below 26 nm. Among them, one of the core hardware systems that affects the accuracy of inspection is the objective lens optical system.

[0021] Therefore, embodiments of the present invention propose a deep ultraviolet objective lens optical system used for object defect inspection. For example, it is used for wafer defect inspection, and wafer defects include, but are not limited to, impurity particle contamination, mechanical scratches, wafer pattern defects, etc. present on the surface. As shown in FIG. 1, the deep ultraviolet objective lens optical system includes a first lens group G1, a second lens group G2, and a third lens group G3 provided in sequence along the same optical axis from the image side to the object side. Here, the refractive powers of the first lens group G1 and the third lens group G3 are both positive, and the refractive power of the first lens group G1 is smaller than that of the third lens group G3. The refractive power of the second lens group G2 is negative. Here, in FIG. 1, the object side is defined as the right side (i.e., the side where the object surface is located), and the image side is defined as the left side.

[0022] According to one possible embodiment of the present invention, the third lens group G3 has a large positive refractive power and is mainly responsible for collecting light ray scattering energy from object defect locations, collecting the light ray scattering energy from the object defect locations at the shortest distance. For example, it collects all light ray scattering energy within the object-side numerical aperture NA=0.965 across the entire field of view, and then aberration correction is performed by the following two lens groups (second lens group G2 and first lens group G1). After the light ray scattering energy from the object is collected by the third lens group G3, it is converted from a large incident angle to a relatively horizontal angle, but some angular difference still exists at different positions, so it is necessary to compensate for each position well through one negative lens group, thereby reducing the difficulty for the next group to correct aberrations and achieving flat-field correction. Therefore, the second lens group G2 has a negative refractive power and is responsible for the function of flat-field correction. After the second lens group G2 completes flat-field correction, all remaining aberrations are higher-order aberrations. In this case, it is necessary to optimize one lens group with weak refractive power to compensate for the higher-order aberrations. Therefore, the first lens group G1 has relatively weak positive refractive power and compensates for the higher-order aberrations.

[0023] According to one possible embodiment of the present invention, the first lens group G1 includes, in order along the same optical axis from the image side to the object side, a first lens 1 having a positive refractive power, a second lens 2 having a positive refractive power, a third lens 3 having a negative refractive power, and a fourth lens 4 having a negative refractive power.

[0024] According to one possible embodiment of the present invention, the second lens group G2 includes, in order along the same optical axis from the image side to the object side, a fifth lens 5 having a positive refractive power and a sixth lens 6 having a positive refractive power.

[0025] According to one possible embodiment of the present invention, the third lens group G3 includes, in order along the same optical axis from the image side to the object side, a seventh lens 7 having negative refractive power, an eighth lens 8 having positive refractive power, a ninth lens 9 having positive refractive power, and a tenth lens 10 having positive refractive power.

[0026] According to one possible embodiment of the present invention, the first lens 1, the fifth lens 5, the sixth lens 6, the ninth lens 9, and the tenth lens 10 are all positive meniscus lenses, and the convex surface of the positive meniscus lens faces the image side.

[0027] The second lens 2 and the eighth lens 8 are both biconvex lenses.

[0028] The third lens 3 and the fourth lens 4 are both negative meniscus lenses, and the concave surface of the negative meniscus lens faces the image side.

[0029] The seventh lens, 7, is a biconcave lens.

[0030] By adopting this embodiment, all lenses employ a spherical design, avoiding the manufacturing difficulties that arise from introducing aspherical or free-form surfaces.

[0031] According to one possible embodiment of the present invention, the aforementioned deep ultraviolet objective lens optical system further includes an aperture diaphragm for limiting the size of the imaging beam. The aperture diaphragm is located on the image side of the first lens group G1, i.e., at the exit of the deep ultraviolet objective lens optical system.

[0032] According to one possible embodiment of the present invention, the first lens group G1, the second lens group G2, and the third lens group G3 all employ fused silica lenses of the deep ultraviolet spectral segment, having a refractive index Nd > 1.45, an Abbe number Vd > 67.8, and good thermal stability. The selected materials are all krypton fluoride KrF grade materials, possessing ultra-high transmittance in the deep ultraviolet spectral segment, with a transmittance of 99.9% or more in the deep ultraviolet 266 nm wavelength segment, and no fluorescence effect. As can be seen from this, the first lens group G1, the second lens group G2, and the third lens group G3 according to the present invention all employ fused silica lenses of the same type of deep ultraviolet spectral segment, possessing good thermal stability and ultra-high transmittance in the deep ultraviolet spectral segment.

[0033] According to one possible embodiment of the present invention, the focal length of the deep ultraviolet objective lens is 50 mm, the overall length of the optical system is less than 200 mm, and the object-side field of view radius is 0.19 mm or less.

[0034] According to one possible embodiment of the present invention, parallel light is emitted from the image side of the optical system, the maximum beam diameter is 96.5 mm, and the diameters of the lenses included in the first lens group G1, the second lens group G2, and the third lens group G3 are all 100.5 mm or less.

[0035] According to one possible embodiment of the present invention, the object-side numerical aperture NA of the deep ultraviolet objective lens is greater than 0.95, the operating wavelength is 266 nm, and the bandwidth is 1 nm. According to the Rayleigh resolution formula σ = 0.61λ / NA (where λ is the operating wavelength), the characteristic resolution σ of the deep ultraviolet objective lens optical system is better than 170 nm. According to the formula for calculating NA and focusing angle θ = arcsin(NA), the scattered light focusing angle θ > 71.5° of the deep ultraviolet objective lens optical system.

[0036] For example, if the numerical aperture NA = 0.965, according to the Rayleigh resolution formula σ = 0.61λ / NA (where λ is the operating wavelength and is equal to 266 nm), the characteristic resolution σ of the deep ultraviolet objective lens optical system is 168 nm. According to the formula for calculating the NA and focusing angle θ = arcsin(NA), the scattered light focusing angle θ of the deep ultraviolet objective lens optical system is 74.7°.

[0037] According to one possible embodiment of the present invention, the focal length range of the first lens group G1 is 260 mm to 280 mm, the focal length range of the second lens group G2 is -275 mm to -220 mm, and the focal length range of the third lens group G3 is 20 mm to 25 mm.

[0038] As can be seen from the deep ultraviolet lens optical system described above, in this invention, the third lens group has a greater refractive power than the first lens group and is responsible for collecting the scattered energy of light rays from the defect location of the object, collecting the scattered energy of light rays from the defect location of the object within a short distance. The second lens group has a negative refractive power and can effectively compensate for angular differences at each position to achieve flat-field correction. The first lens group has a relatively weak positive refractive power and can compensate for higher-order aberrations. The combination of these three specific lens groups can effectively guarantee the accuracy of imaging.

[0039] In this invention, the field of view radius on the object side is 0.19 mm or less, meaning the total field of view is 0.38 mm or less. On the other hand, the field of view of a conventional objective lens with an object-side numerical aperture (NA) of 0.9 is typically 0.1 mm. Therefore, the total field of view of this invention is approximately four times that of a typical field of view, providing a large field of view characteristic. In this invention, the object-side numerical aperture (NA) of the deep ultraviolet objective lens is greater than 0.95, the operating wavelength is 266 nm, and the bandwidth is 1 nm. Therefore, the optical system possesses both a large numerical aperture and high-resolution characteristics.

[0040] A schematic diagram of the optical path of the deep ultraviolet objective lens optical system according to an embodiment of the present invention is shown in Figure 2, where the line labeled L in Figure 2 represents the optical path of the deep ultraviolet objective lens optical system. In this optical system, the third lens group G3, which is close to the object plane, is responsible for a large positive refractive power. It collects all the scattered light energy within the object-side numerical aperture NA=0.965 for the entire field of view, and at the same time has a large refraction of light rays. Therefore, the second lens group G2 has a negative refractive power, thereby performing flat-field correction on the image plane and reducing the difficulty of aberration correction for the next group. The first lens group G1 has a relatively weak positive refractive power and compensates for higher-order aberrations. By introducing two consecutive meniscus lenses, the third lens 3 and the fourth lens 4, the higher-order spherical aberration caused by the third lens group G3 is balanced, achieving imaging performance that combines high resolution and a large field of view.

[0041] Figure 3 shows an imaging spot diagram of the deep ultraviolet objective lens optical system according to an embodiment of the present invention. The horizontal coordinate represents the image plane size, and the vertical coordinate represents the scale bar. Within the entire field of view, the imaging spot shape is close to circular, there is no obvious coma aberration or astigmatism, and it has good imaging quality.

[0042] A schematic diagram of the imaging energy concentration of a deep ultraviolet objective lens optical system according to an embodiment of the present invention is shown in Figure 4. The horizontal coordinate represents the image plane diameter, and the vertical coordinate represents the ratio of the enclosed energy. Within the entire field of view, the 90% energy concentration can be smaller than the region with a radius of 1 μm, indicating that the deep ultraviolet objective lens optical system can effectively concentrate the focused wafer defect scattered light into the detection optical path. Curves A, B, C, D, and E represent the energy concentration within the corresponding radius ranges for field of view sizes of 0.0000 mm, 0.0965 mm, 0.01365 mm, 0.1671 mm, and 0.1930 mm, respectively.

[0043] In the embodiment of the present invention, telecentricity ensures relatively consistent resolution across the entire field of view on the object side, and also guarantees uniformity of coaxial illumination. A schematic diagram of the imaging telecentricity of the deep ultraviolet objective lens optical system according to the embodiment of the present invention is shown in Figure 5. The horizontal coordinate represents the field of view, and the vertical coordinate represents the emission angle. Lines a, b, and c represent the emission angles of the +Ymax ray, principal ray, and -Ymax ray in different fields of view, respectively. In the embodiment of the present invention, the maximum imaging angle of the principal ray is 0.6 degrees, which indicates that the telecentricity of the system is good.

[0044] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. Each embodiment of this specification is described in a progressive manner, and any identical or similar parts between embodiments should be referenced to one another, while each embodiment focuses on the parts that differ from the others.

[0045] According to another embodiment, a deep ultraviolet objective lens is provided. The deep ultraviolet objective lens includes the deep ultraviolet objective lens optical system shown in Figure 1. All lenses in the deep ultraviolet objective lens optical system are coated on both sides with an anti-reflective coating, thereby reducing or eliminating reflected light from the lens surface and improving image quality. The deep ultraviolet objective lens further includes a barrel, a threaded member, and a rear focal plane of the objective lens. The barrel is the physical housing of the deep ultraviolet objective lens and is generally made of brass. The threaded member is used to attach the objective lens to the objective lens revolving nosepiece of a microscope, and its specifications usually meet Royal Microscopical Society (RMS) standards. The rear focal plane of the objective lens is a hole or aperture through which light rays enter the objective lens.

[0046] According to another embodiment, a wafer inspection microscope is provided. The optical portion of the wafer inspection microscope includes the deep ultraviolet objective lens described above, which is mounted on a revolving nosepiece at the lower end of the microscope tube and is divided into low-magnification, medium-magnification, and high-magnification deep ultraviolet objective lenses depending on the magnification. The deep ultraviolet objective lens includes the deep ultraviolet objective lens optical system shown in Figure 1. The optical portion of the wafer inspection microscope further includes an eyepiece that delivers a magnified image to the observer's eye. The mechanical portion of the wafer inspection microscope is the basic support portion of the microscope and mainly includes a mirror base, mirror column, and arm. The mirror base is the base of the wafer inspection microscope and is used to support the entire microscope body. The mirror column connects the mirror base and the arm. The arm is the part that is held by hand when handling the wafer inspection microscope. The illumination portion of the wafer inspection microscope is located below the mirror table and includes a reflector and a light condenser. The reflector can rotate in any direction and has both a flat and a concave side, which are applied to environments with strong and weak light rays, respectively. The light condenser consists of a focusing lens and an aperture, and can concentrate light rays onto the object being observed. The focusing section of the wafer inspection microscope includes a coarse adjustment and a fine adjustment. The coarse adjustment is used to quickly adjust the distance between the deep ultraviolet objective lens and the object. The fine adjustment is used to obtain a clearer image of the object when using a high-magnification deep ultraviolet objective lens. The wafer inspection microscope further includes a stage, which is a platform beneath the microscope and is used to place the object being observed. The stage is generally made of metal or glass and is movable from side to side to facilitate observation of different parts of the object.

[0047] The technical proposal according to the present invention has been described in detail above. While this paper has explained the principles and embodiments of the present invention using specific examples, the above descriptions of examples are merely for understanding the method and core concept of the present invention. Furthermore, those skilled in the art may modify specific embodiments and scope of application based on the concept of the present invention. In other words, the contents of this specification should not be understood as limitations on the present invention.

Claims

1. A deep ultraviolet objective lens optical system, It includes a first lens group, a second lens group, and a third lens group arranged sequentially along the same optical axis from the image side to the object side, The refractive powers of both the first lens group and the third lens group are positive, and the refractive power of the first lens group is less than the refractive power of the third lens group. The refractive power of the second lens group is negative. A deep ultraviolet objective lens optical system characterized by the following features.

2. The first lens group includes, in order along the same optical axis from the image side to the object side, a first lens having positive refractive power, a second lens having positive refractive power, a third lens having negative refractive power, and / or a fourth lens having negative refractive power, The second lens group includes, in order along the same optical axis from the image side to the object side, a fifth lens having positive refractive power and a sixth lens having positive refractive power, and / or The third lens group includes, in order along the same optical axis from the image side to the object side, a seventh lens having negative refractive power, an eighth lens having positive refractive power, a ninth lens having positive refractive power, and a tenth lens having positive refractive power. The optical system according to claim 1.

3. The first, fifth, sixth, ninth, and tenth lenses are all positive meniscus lenses, and the convex surface of the positive meniscus lens faces the image side. The second lens and the eighth lens are both biconvex lenses. The third and fourth lenses are both negative meniscus lenses, and the concave surface of the negative meniscus lens faces the image side. The seventh lens is a biconcave lens. The optical system according to claim 2.

4. Further including an aperture diaphragm, The aperture diaphragm is located on the image side of the first lens group. The optical system according to claim 1.

5. The first lens group, the second lens group, and the third lens group all use fused silica lenses in the deep ultraviolet spectral segment. The optical system according to claim 1.

6. The object-side numerical aperture (NA) of the deep ultraviolet objective lens is greater than 0.95, the focal length of the deep ultraviolet objective lens is 50 mm, the total length of the optical system is less than 200 mm, and the field of view radius on the object side is 0.19 mm or less. The optical system according to claim 1.

7. The light emitted from the image side of the optical system is parallel light, and the apertures of the lenses included in the first lens group, the second lens group, and the third lens group are all 100.5 mm or less. The optical system according to claim 1.

8. The focal length of the first lens group is 260 mm to 280 mm, the focal length of the second lens group is -275 mm to -220 mm, and the focal length of the third lens group is 20 mm to 25 mm. The optical system according to claim 1.

9. It is a deep ultraviolet objective lens, The optical system includes the one described in any one of claims 1 to 8. A deep ultraviolet objective lens characterized by the following features.

10. A microscope for wafer inspection, Including the deep ultraviolet objective lens described in claim 9, A microscope for wafer inspection characterized by the following features.

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