Deep ultraviolet objective lens optical system, deep ultraviolet objective lens and wafer detection microscope

Abstract

The deep ultraviolet objective optical system comprises a first lens group, a second lens group and a third lens group which are sequentially arranged along the same optical axis from an image space to an object space, wherein the diopters of the first lens group and the third lens group are positive, and the focal power of the first lens group is smaller than that of the third lens group; the diopter of the second lens group is negative. Compared with the first lens group, the third lens group has larger focal power so as to be responsible for collecting light scattering energy at the defect position of an object and collecting the light scattering energy at the defect position of the object in a short distance, and the second lens group has negative focal power, so that angle difference of all the positions can be well compensated to realize flat field correction, and the imaging quality is improved. The first lens group has weak positive focal power and can compensate for high-order phase difference, and the imaging accuracy can be effectively guaranteed through the combination of the three specific lens groups.

Description

Technical Field

[0001] The present application relates to the technical field of optical instruments, and in particular to a deep ultraviolet objective optical system, a deep ultraviolet objective, and a wafer inspection microscope. Background Art

[0002] With the rapid development of the country's semiconductor chip field, import substitution of wafer detection related equipment is imperative. Wafer surface particle detection equipment is mainly used to identify and locate problems such as impurity particle contamination, mechanical scratches, and wafer pattern defects on the product surface. Wafer defects may cause leakage and power failure of semiconductor products during use, affecting the chip yield. Therefore, it is necessary to detect wafer defects to improve the chip yield. Before performing wafer defect detection, it is necessary to collect the light scattering energy at the wafer defect position, and the deep ultraviolet objective lens assumes this function. The deep ultraviolet objective lens has a greater impact on the accuracy of imaging. Therefore, how to provide a deep ultraviolet objective lens optical system to ensure imaging accuracy has become a technical problem that needs to be solved urgently. Summary of the invention

[0003] The present application provides a deep ultraviolet objective optical system, a deep ultraviolet objective and a wafer inspection microscope to ensure imaging accuracy.

[0004] This application provides the following solutions:

[0005] According to a first aspect, there is provided a deep ultraviolet objective optical system, comprising:

[0006] A first lens group, a second lens group, and a third lens group are arranged in sequence along the same optical axis from the image side to the object side;

[0007] The refractive powers of the first lens group and the third lens group are both positive, and the optical power of the first lens group is smaller than the optical power of the third lens group;

[0008] The refractive power of the second lens group is negative.

[0009] According to a possible implementation of the present application, the first lens group includes, from the image side to the object side along the same optical axis direction, in sequence: a first lens with positive optical power, a second lens with positive optical power, a third lens with negative optical power, and a fourth lens with negative optical power; and / or,

[0010] The second lens group includes, in sequence from the image side to the object side along the same optical axis direction: a fifth lens having positive refractive power and a sixth lens having positive refractive power; and / or,

[0011] The third lens group includes, from the image side to the object side along the same optical axis direction, a seventh lens with negative optical power, an eighth lens with positive optical power, a ninth lens with positive optical power, and a tenth lens with positive optical power.

[0012] According to a possible implementation of the present application, the first lens, the fifth lens, the sixth lens, the ninth lens and the tenth lens are all positive meniscus lenses, and the convex surface of the positive meniscus lens faces the image side;

[0013] The second lens and the eighth lens are both biconvex lenses;

[0014] The third lens and the fourth lens are both negative meniscus lenses, and the concave surface of the negative meniscus lens faces the image side;

[0015] The seventh lens is a biconcave lens.

[0016] According to a possible implementation of the present application, the further comprising: an aperture stop, wherein the aperture stop is on the image side of the first lens group.

[0017] According to a possible implementation of the present application, the first lens group, the second lens group, and the third lens group all use deep ultraviolet spectral fused silica lenses.

[0018] According to a possible implementation of the present application, the object side numerical aperture NA (Numerical Aperture, numerical aperture) of the deep ultraviolet objective lens is greater than 0.95, 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 less than or equal to 0.19 mm.

[0019] According to a possible implementation of the present application, the image-side emission 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 less than or equal to 100.5 mm.

[0020] According to a possible implementation of the present application, the focal length of the first lens group is between 260 mm and 280 mm, the focal length of the second lens group is between -275 mm and -220 mm, and the focal length of the third lens group is between 20 mm and 25 mm.

[0021] According to a second aspect, a deep ultraviolet objective lens is provided, comprising the optical system of the first aspect.

[0022] According to a third aspect, there is provided a wafer inspection microscope, the wafer inspection microscope comprising the deep ultraviolet objective lens of the second aspect, the deep ultraviolet objective lens comprising the optical system of the first aspect.

[0023] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0024] 1) In the present application, the third lens group has a larger optical focal length than the first lens group, so as to collect the light scattering energy at the defect position of the object and collect the light scattering energy at the defect position of the object within a short distance. The second lens group has a negative optical focal length, which can well compensate for the angle difference of each position to achieve flat field correction. The first lens group has a weaker positive optical focal length, which can compensate for high-order phase differences. The combination of these three specific lens groups can effectively ensure the accuracy of imaging.

[0025] 2) All lenses in this application adopt a spherical design to avoid the problem of manufacturing difficulties caused by the introduction of aspherical surfaces or free-form surfaces.

[0026] 3) In the present application, the first lens group, the second lens group and the third lens group all use the same deep ultraviolet spectral band fused silica lens, which has good thermal stability and ultra-high transmittance in the deep ultraviolet spectral band.

[0027] 4) The object field radius in the present application is less than or equal to 0.19 mm, that is, the full field of view is less than or equal to 0.38 mm. The general field of view of a conventional objective lens with an object numerical aperture NA of 0.9 is 0.1 mm. Therefore, the full field of view of the present application is about 4 times that of the general field of view, has a large field of view characteristic, and the overall length is also optimized.

[0028] 5) The object side numerical aperture NA of the deep ultraviolet objective lens in the present application is greater than 0.95, the working wavelength is 266nm, and the bandwidth is 1nm, so that the optical system has a large numerical aperture and high resolution characteristics.

[0029] Of course, any product implementing the present application does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A deep ultraviolet objective optical system provided in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of the optical path of a deep ultraviolet objective optical system provided in an embodiment of the present application;

[0033] Figure 3The imaging point diagram of the deep ultraviolet objective optical system provided in the embodiment of the present application;

[0034] Figure 4 A schematic diagram of the imaging energy concentration of a deep ultraviolet objective optical system provided in an embodiment of the present application;

[0035] Figure 5 A schematic diagram of the imaging telecentricity of the deep ultraviolet objective optical system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments in the present application belong to the scope of protection of this application.

[0037] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0038] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0039] The directions or positional relationships such as "upper", "lower", "front", "back", "left", and "right" involved in the embodiments of the present application are only for the convenience of describing the present application, and are not intended to limit the devices or components of the present disclosure to have specific directions or positions. It should be understood that the expressions of these directions or positional relationships are all relative. Any modifications, equivalent substitutions, improvements, etc. made within the scope of the present disclosure shall be included in the protection scope of the present disclosure.

[0040] Currently, monitoring the process through wafer defect detection can reduce production losses and improve process yield. Among all semiconductor inspection equipment, the majority of equipment uses optical inspection technology, covering all advanced processes of 26nm and below. One of the core hardware systems that affects the accuracy of inspection is the objective optical system.

[0041] Therefore, the present application embodiment proposes a deep ultraviolet objective optical system for object defect detection. For example, wafer defect detection, wafer defects include but are not limited to foreign particle contamination on the surface, mechanical scratches, wafer pattern defects, etc. Figure 1 As shown, the deep ultraviolet objective optical system includes: a first lens group G1, a second lens group G2 and a third lens group G3 arranged in sequence along the same optical axis from the image side to the object side. The refractive powers of the first lens group G1 and the third lens group G3 are both positive, and the optical power of the first lens group G1 is less than the optical power of the third lens group G3. The refractive power of the second lens group G2 is negative. The definition Figure 1 The object side is the right side, where the object surface is located, and the image side is the left side.

[0042] According to a possible implementation of the present application, the third lens group G3 has a large positive focal length, and is mainly responsible for collecting the light scattering energy at the defect position of the object, and collects the light scattering energy at the defect position of the object within the shortest distance. For example, all light scattering energy within the full field of view object numerical aperture NA=0.965 is collected, and then aberration correction is performed through the subsequent two groups of lenses (the second lens group G2 and the first lens group G1). After the light scattering energy of the object is collected by the third lens group G3, it is converted from a large incident angle to a relatively horizontal angle, but there are still certain angle differences at different positions, so a group of negative lens groups is needed to compensate for each position well, reduce the difficulty of aberration correction of the rear group, and achieve flat field correction. Therefore, the second lens group G2 has a negative focal length and assumes the flat field correction function. After the second lens group G2 completes the flat field correction, the remaining aberrations are all high-order aberrations. At this time, it is necessary to optimize a group of lens groups with weak focal lengths to compensate for high-order aberrations. Therefore, the first lens group G1 has a weak positive focal length, which compensates for high-order aberrations.

[0043] According to a possible implementation of the present application, the first lens group G1 includes, in sequence from the image side to the object side along the same optical axis direction: a first lens 1 with positive optical power, a second lens 2 with positive optical power, a third lens 3 with negative optical power and a fourth lens 4 with negative optical power.

[0044] According to a possible implementation of the present application, the second lens group G2 includes, in sequence from the image side to the object side along the same optical axis direction: a fifth lens 5 with positive refractive power and a sixth lens 6 with positive refractive power.

[0045] According to a possible implementation of the present application, the third lens group G3 includes, from the image side to the object side along the same optical axis direction, in sequence: a seventh lens 7 with negative optical power, an eighth lens 8 with positive optical power, a ninth lens 9 with positive optical power, and a tenth lens 10 with positive optical power.

[0046] According to a possible implementation of the present application, 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.

[0047] The second lens 2 and the eighth lens 8 are both biconvex lenses.

[0048] The third lens 3 and the fourth lens 4 are both negative meniscus lenses, and the concave surfaces of the negative meniscus lenses face the image side.

[0049] The seventh lens 7 is a biconcave lens.

[0050] With this implementation method, all lenses are designed with spherical surfaces, avoiding the problem of manufacturing difficulties caused by the introduction of aspherical surfaces or free-form surfaces.

[0051] According to a possible implementation of the present application, the aforementioned deep ultraviolet objective optical system further includes: an aperture stop for limiting the size of the imaging beam. The aperture stop is located on the image side of the first lens group G1, that is, at the exit of the deep ultraviolet objective optical system.

[0052] According to a possible implementation of the present application, the first lens group G1, the second lens group G2 and the third lens group G3 all use deep ultraviolet spectral fused silica lenses, with a refractive index Nd>1.45, a dispersion coefficient Vd>67.8, and good thermal stability. The selected materials are all krypton fluoride KrF grade materials, which have ultra-high transmittance in the deep ultraviolet spectral band, and a transmittance greater than 99.9% in the deep ultraviolet 266nm band, without fluorescence effect. It can be seen that the first lens group G1, the second lens group G2 and the third lens group G3 in the present application all use the same deep ultraviolet spectral fused silica lens, which has good thermal stability and ultra-high transmittance in the deep ultraviolet spectral band.

[0053] According to a possible implementation of the present application, 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 field radius is less than or equal to 0.19 mm.

[0054] According to a possible implementation of the present application, the image-side emission of the optical system is parallel light, 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 less than or equal to 100.5 mm.

[0055] According to a possible implementation of the present application, the object numerical aperture NA of the deep ultraviolet objective lens is greater than 0.95, the operating wavelength is 266nm, and the bandwidth is 1nm. According to the Rayleigh resolution formula: σ = 0.61λ / NA, λ is the operating wavelength, therefore, the characteristic resolution σ of the deep ultraviolet objective lens optical system is better than 170nm. According to the NA and collection angle calculation formula θ = arcsin (NA), the scattered light collection angle θ of the deep ultraviolet objective lens optical system is > 71.5°.

[0056] For example, the numerical aperture NA = 0.965, according to the Rayleigh resolution formula: σ = 0.61λ / NA, λ is the working wavelength, which is equal to 266nm, so the characteristic resolution σ of the deep ultraviolet objective optical system is 168nm. According to the calculation formula of NA and collection angle, θ = arcsin (NA), the scattered light collection angle of the deep ultraviolet objective optical system θ = 74.7°.

[0057] According to a possible implementation of the present application, the focal length of the first lens group G1 is between 260 mm and 280 mm, the focal length of the second lens group G2 is between -275 mm and -220 mm, and the focal length of the third lens group G3 is between 20 mm and 25 mm.

[0058] It can be seen from the above-mentioned deep ultraviolet lens optical system that the third lens group in the present application has a larger optical focal length than the first lens group, so as to be responsible for collecting the light scattering energy at the defect position of the object, and collect the light scattering energy at the defect position of the object within a short distance. The second lens group has a negative optical focal length, which can well compensate for the angle difference of each position to achieve flat field correction. The first lens group has a weaker positive optical focal length, which can compensate for high-order phase differences. The combination of these three specific lens groups can effectively ensure the accuracy of imaging.

[0059] The object field radius in the present application is less than or equal to 0.19mm, that is, the full field of view is less than or equal to 0.38mm. The general field of view of the conventional object lens with an object numerical aperture NA of 0.9 is 0.1mm. Therefore, the full field of view of the present application is about 4 times the general field of view, and has a large field of view characteristic. The object numerical aperture NA of the deep ultraviolet objective lens in the present application is greater than 0.95, the operating wavelength is 266nm, and the bandwidth is 1nm, so that the optical system has a large numerical aperture while also having high resolution characteristics.

[0060] The schematic diagram of the optical path of the deep ultraviolet objective optical system described in the embodiment of the present application is as follows Figure 2 As shown, Figure 2The line marked with L represents the optical path of the deep ultraviolet objective optical system. In this optical system, the third lens group G3 close to the object plane has a large positive focal length. While collecting all the scattered light energy within the full field of view object numerical aperture NA=0.965, the light is greatly deflected. Therefore, the second lens group G2 has a negative focal length, performs flat field correction on the image field, and reduces the difficulty of aberration correction in the rear group. The first lens group G1 has a weaker positive focal length and compensates for high-order aberrations. By introducing two consecutive meniscus lenses, the third lens 3 and the fourth lens 4, the high-order spherical aberration caused by the third lens group G3 is balanced, achieving imaging performance that takes into account both high resolution and a large field of view.

[0061] The imaging point diagram of the deep ultraviolet objective optical system provided in the embodiment of the present application is as follows: Figure 3 As shown. The horizontal axis represents the image plane size, and the vertical axis represents the scale bar. The imaging spot shape is relatively round in the full field of view, with no obvious coma or astigmatism, and has good imaging quality.

[0062] The schematic diagram of the imaging energy concentration of the deep ultraviolet objective optical system provided in the embodiment of the present application is as follows Figure 4 As shown. The horizontal axis represents the image diameter, and the vertical axis represents the closed energy ratio. 90% of the energy concentration in the full field of view can be better than the area with a radius of 1μm, indicating that the deep ultraviolet objective optical system can well concentrate the collected wafer defect scattered light into the detection light path. Curves A, B, C, D, and E represent the energy concentration within the corresponding radius when the field of view is 0.0000mm, 0.0965mm, 0.01365mm, 0.1671mm, and 0.1930mm, respectively.

[0063] In the embodiment of the present application, the telecentricity is to ensure that the whole field of view of the object side obtains relatively consistent resolution, and also to ensure the uniformity of coaxial illumination. The schematic diagram of the imaging telecentricity of the deep ultraviolet objective optical system provided in the embodiment of the present application is as follows: Figure 5 As shown. The horizontal axis represents the field of view, and the vertical axis represents the angle of incidence. Lines a, b, and c represent the angles of incidence of +Ymax light, main light, and -Ymax light under different fields of view, respectively. The maximum imaging angle of the main light in the embodiment of the present application is 0.6 degrees, indicating that the telecentricity of the system is good.

[0064] The above is a description of a specific embodiment of this specification. Other embodiments are within the scope of the attached claims. Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments.

[0065] According to another embodiment, a deep ultraviolet objective lens is provided. The deep ultraviolet objective lens comprises Figure 1The deep ultraviolet objective optical system shown in the figure. The front and back surfaces of all lenses in the deep ultraviolet objective optical system are coated with anti-reflection films to reduce or eliminate the reflected light on the lens surface, thereby improving the imaging quality. The deep ultraviolet objective also includes a lens barrel, a thread and a rear focal plane of the objective. The lens barrel is the physical shell of the deep ultraviolet objective, which is usually made of brass. The thread is used to mount the objective onto the microscope objective turret, and its specifications usually meet the standards of the Royal Microscopical Society. The rear focal plane of the objective is the hole or opening through which light enters the objective.

[0066] According to another embodiment, a wafer inspection microscope is provided. The optical part of the wafer inspection microscope includes the aforementioned deep ultraviolet objective lens, which is mounted on a rotator at the lower end of the lens barrel and is divided into low-power, medium-power and high-power deep ultraviolet objective lenses according to different magnifications. The deep ultraviolet objective lens includes Figure 1 The deep ultraviolet objective optical system shown in the figure. The optical part of the wafer inspection microscope also includes an eyepiece for transmitting the magnified image to the eyes of the observer. The mechanical part of the wafer inspection microscope is the basic support part of the microscope, which mainly includes a mirror base, a mirror column and a mirror arm. The mirror base is the base of the wafer inspection microscope, which is used to support the entire mirror body; the mirror column connects the mirror base and the mirror arm. The mirror arm is the part that is held by hand when taking and placing the wafer inspection microscope. The lighting part of the wafer inspection microscope is located below the stage, including a reflector and a light collector. The reflector can be rotated in any direction and has a flat and concave surface, which are respectively suitable for environments with strong and weak light. The light collector is composed of a condenser and an aperture, which can focus light on the object to be observed. The focusing part of the wafer inspection microscope includes a coarse adjuster and a fine adjuster. The coarse adjuster is used to quickly adjust the distance between the deep ultraviolet objective lens and the object. The fine adjuster is used to obtain a clearer image when using a high-power deep ultraviolet objective lens. The wafer inspection microscope also includes a stage, which is a platform under the microscope for placing the object to be observed. The stage is generally made of metal or glass and can be moved left and right to observe objects in different parts.

[0067] The technical solution provided by the present application is described in detail above. The principle and implementation method of the present application are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A deep ultraviolet objective optical system, characterized in that: include: A first lens group, a second lens group, and a third lens group are arranged in sequence along the same optical axis from the image side to the object side; The refractive powers of the first lens group and the third lens group are both positive, and the optical power of the first lens group is smaller than the optical power of the third lens group; The refractive power of the second lens group is negative.

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

3. The optical system according to claim 2, characterized in that The first lens, the fifth lens, the sixth lens, the ninth lens and the tenth lens 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 lens and the fourth lens 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.

4. The optical system according to any one of claims 1 to 3, characterized in that: Also includes: An aperture stop is located on the image side of the first lens group.

5. The optical system according to any one of claims 1 to 3, characterized in that: The first lens group, the second lens group and the third lens group all adopt deep ultraviolet spectral band fused silica lenses.

6. The optical system according to any one of claims 1 to 3, characterized in that: 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 overall length of the optical system is less than 200 mm, and the object side field of view radius is less than or equal to 0.19 mm.

7. The optical system according to any one of claims 1 to 3, characterized in that: The image-side emission 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 less than or equal to 100.5 mm.

8. The optical system according to any one of claims 1 to 3, characterized in that: The focal length of the first lens group is between 260 mm and 280 mm, the focal length of the second lens group is between -275 mm and -220 mm, and the focal length of the third lens group is between 20 mm and 25 mm.

9. A deep ultraviolet objective lens, characterized in that: The deep ultraviolet objective lens comprises the optical system as described in any one of claims 1-8.

10. A wafer inspection microscope, characterized in that: The wafer inspection microscope comprises the deep ultraviolet objective lens as claimed in claim 9, and the deep ultraviolet objective lens comprises the optical system as claimed in any one of claims 1-8.

Images