Light spot shrinking device for angle resolution scatterometer

Abstract

The invention belongs to the field of optics, and particularly discloses a light spot shrinking device for an angle resolution scatterometer. Through the first lens, the beam shaping element and the second lens which are sequentially arranged along the light path, beam focusing, beam shaping and collimation are carried out in sequence, the collimated beam with the diameter smaller than that of the beam of the light source is formed, the collimated beam is combined with the subsequent light path, and the light spot shrinking function can be achieved at the detection end of the objective lens.

Description

Technical Field

[0001] This application belongs to the field of optics, and more specifically, relates to a spot-size reduction device for an angular resolution scatterometer. Background Art

[0002] An angular resolution scatterometer is a three-channel imaging polarization scatterometer with polarization imaging. A detection spot is generated by converging a light spot through a high numerical aperture (NA) objective lens. The detection spot irradiates the surface of a sample to generate a scattering signal. After a group of conjugate lenses, the scattered radio frequency domain image and the spatial image on the back focal plane of the objective lens are respectively imaged onto three cameras of three channels. Among them, the spatial image channel serves as a microscope for observing the microscopic morphology of the sample. The frequency domain image channel divides the scattering signal into a P-polarized state light beam and an S-polarized state light beam through polarization devices and images them onto the CCD cameras of the two channels of the frequency domain image.

[0003] The detection spot is a key signal carrier in the measurement process of an angular resolution polarization scatterometer, and its characteristics and positioning directly affect the accuracy and precision of the measurement results. The DBO method measures the overlay errors in two mutually perpendicular directions by measuring a set of overlay marks. This method requires the detection spot to be smaller than each small unit of the overlay marks. Currently, the sizes of DBO marks in the wafer channels mainly include 8 um and 20 um. Therefore, strict requirements are imposed on the detection spot. Moreover, with the continuous continuation of Moore's Law, the critical dimensions are gradually shrinking, and more stringent requirements for the detection spot will be imposed in the future. Therefore, it is necessary to propose a spot-size reduction technology for the measurement of an angular resolution polarization scatterometer with an ultra-small light spot. Summary of the Invention

[0004] Aiming at the defects of the prior art, the purpose of this application is to provide a spot-size reduction device for an angular resolution scatterometer, aiming to solve the problem of the over-large detection spot of the angular resolution polarization scatterometer.

[0005] This application relates to a spot-size reduction device for an angular resolution scatterometer, which sequentially includes a first lens, a beam shaping element, and a second lens along the optical path; Among them, the incident collimated beam of the angular resolution scatterometer forms a focused beam at the focal point after passing through the first lens. After passing through the beam shaping element, the focused beam forms a beam with a smaller beam diameter and a certain divergence angle, and the divergent beam is collimated and output through the second lens.

[0006] Preferably, the beam shaping element is a pinhole aperture located at the rear focal point of the first lens.

[0007] Preferably, the beam shaping element includes: a speckle-reducing element located at the rear focal point of the first lens and a pinhole aperture located behind the speckle-reducing element; Among them, after the focused beam passes through the speckle reduction element, the speckle is attenuated to form a low-speckle beam; after the low-speckle beam passes through the pinhole aperture, a beam with a smaller beam diameter and a certain divergence angle is formed, and the divergent beam is collimated by the second lens.

[0008] Preferably, the speckle reduction element is composed of a scattering glass sheet and a rotating motor. The scattering glass sheet is perpendicular to the optical path, and the rotating motor drives the scattering glass sheet to rotate perpendicular to the optical path, and the rotation frequency is higher than the sampling frequency of the imaging device.

[0009] Preferably, the focused beam is as close as possible to the edge of the scattering glass sheet.

[0010] Preferably, the distance between the speckle reduction element and the pinhole aperture is 1 mm - 2 mm.

[0011] Preferably, the diameter of the pinhole aperture , the focal length of the second lens and the reduced spot diameter satisfy the following formula:

[0012] Among them, is the focal length of the first conjugate lens, is the tube lens focal length of the objective lens, is the focal length of the second conjugate lens, is the magnification of the objective lens. The first conjugate lens, the objective lens and the second conjugate lens all come from the angular resolution scatterometer.

[0013] Preferably, the reduced spot diameter does not exceed 5 μm.

[0014] Preferably, the first lens is an achromatic doublet lens.

[0015] Preferably, the distance between the first lens and the collimating lens forming the incident collimated beam is the sum of their focal lengths.

[0016] Generally speaking, compared with the prior art by the above technical solution conceived by the present application, the following beneficial effects are obtained: The present application provides a spot reduction device for an angular resolution scatterometer. By sequentially arranging a first lens, a beam shaping element and a second lens along the optical path, beam focusing, beam shaping and collimation are successively performed to form a collimated beam with a smaller beam diameter than the beam of the light source. Combined with the subsequent optical path, the function of spot reduction can be achieved at the detection end of the objective lens. Description of the Drawings

[0017] Figure 1 is a schematic structural diagram of a spot reduction device for an angular resolution scatterometer provided by an embodiment of the present application Figure 1 .

[0018] Figure 2 This is a schematic structure diagram of a spot - shrinking device for an angular - resolved scatterometer provided by an embodiment of the present application. Figure 2 。

[0019] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 10 - Light source, 20 - Collimating lens, 30 - First lens, 40 - Speckle - reducing element, 50 - Pinhole aperture, 60 - Second lens. Specific embodiments

[0020] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0021] The embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application.

[0022] As Figure 1 shown, the present application discloses a spot - shrinking device for an angular - resolved scatterometer, which is characterized in that it sequentially includes a first lens 30, a beam - shaping element, and a second lens 60 along the optical path; Among them, after the incident collimated beam of the angular - resolved scatterometer passes through the first lens 30, a focused beam is formed at the focal point. After the focused beam passes through the beam - shaping element, a beam with a smaller beam diameter and a certain divergence angle is formed, and the divergent beam is collimated and output by the second lens 60.

[0023] The incident collimated beam of the angular - resolved scatterometer is the light emitted by the light source 10 and forms a beam with high parallelism after being collimated by the collimating lens 20. The beam output after being collimated by the second lens 60 enters the filter, polarizer, wave plate, aperture, conjugate lens group, beam splitter, and objective lens in the incident optical path of the polarization - resolved scatterometer to jointly complete the reduction of the detection spot.

[0024] Preferably, as Figure 1 shown, the beam - shaping element is a pinhole aperture 50 located at the rear focal point of the first lens.

[0025] Preferably, as Figure 2 shown, the beam - shaping element includes: a speckle - reducing element 40 located at the rear focal point of the first lens and a pinhole aperture 50 located behind the speckle - reducing element 40; Among them, after the focused beam passes through the speckle - reducing element 40, the attenuation of the speckle is carried out to form a low - speckle beam; after the low - speckle beam passes through the pinhole aperture 50, a beam with a smaller beam diameter and a certain divergence angle is formed, and the divergent beam is collimated by the second lens 60.

[0026] It should be noted that in this application, a speckle elimination element located at the converging light spot is preferably added, which can not only make the scattered light passing through the speckle attenuator easier to be collected, but also make the effect of speckle attenuation better, especially suitable for light sources with serious speckles such as coherent light sources. The pinhole aperture should be installed as close as possible to the output end of the speckle attenuator.

[0027] Preferably, the speckle elimination element is composed of a scattering glass sheet and a rotating motor. The scattering glass sheet is perpendicular to the optical path, and the rotating motor drives the scattering glass sheet to rotate perpendicular to the optical path, and the rotation frequency is higher than the sampling frequency of the imaging device. The structure of the speckle elimination element proposed in this application can homogenize the speckles of the laser light source and the significantly uneven light beam into a light beam with an intensity difference within 15% of the intensity fluctuation throughout the light beam, and the material cost is about 800 yuan.

[0028] Preferably, the focused light beam is as close as possible to the edge of the scattering glass sheet. Since the scattering glass sheet rotates along the central axis of the scattering glass sheet, the closer to the edge, the higher the rotation speed, and the more the scattering glass sheet acts on the focused light beam, the better the speckle elimination effect.

[0029] Preferably, the distance between the speckle elimination element and the pinhole aperture is 1 mm - 2 mm.

[0030] Preferably, the diameter of the pinhole aperture , the focal length of the second lens and the diameter of the reduced light spot satisfy the following formula:

[0031] where is the focal length of the first conjugate lens, is the tube lens focal length of the objective lens, is the focal length of the second conjugate lens, is the magnification of the objective lens. The first conjugate lens, the objective lens and the second conjugate lens all come from the angular resolution scatterometer. Through the above formula, the appropriate models of the pinhole aperture and the collimating lens are selected to achieve the reduction of the detection light spot and the adjustment of the light spot size.

[0032] Preferably, the diameter of the reduced light spot does not exceed 5 μm.

[0033] Preferably, the first lens is an achromatic doublet lens, which can achieve a smaller converging light spot at the focal point.

[0034] Preferably, the distance between the first lens and the collimating lens forming the incident collimated light beam is the sum of their focal lengths. This configuration can more effectively focus the light beam onto a point, optimize the performance of the optical system, and achieve a better imaging effect.

[0035] In this embodiment, the diameter of the light source beam is 800 μm, the diameter of the pinhole aperture is 400 μm, and the beam output by the spot shrinking device becomes the beam corresponding to a 400-μm point light source, which can better adapt to the incident light path of the subsequent angular resolution polarization scatterometer.

[0036] The subsequent light path process is as follows: The collimated beam output by the spot shrinking device passes through a filter to filter the beam and form a filtered beam; the polarizer and wave plate change the polarization state of the beam to form incident light with a certain polarization state; the aperture adjusts the incident angle and azimuth angle of the beam entering the rear focal plane of the objective lens in the subsequent stage, and can filter out part of the zero-order scattered light of the scatterometer, so that the scattered light of the positive and negative first and second orders in the frequency-domain image of the scatterometer will not overlap with the zero-order light; subsequently, through a set of conjugate lenses, the shape of the aperture is transmitted to the rear focal plane of the objective lens through the scaling of the conjugate lenses to achieve the control of the incident angle and azimuth angle of the incident light at the objective lens. The incident light converges at the objective lens to form a detection spot with a size on the order of micrometers.

[0037] It should be understood that expressions such as "including" and "may include" that can be used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "including" and / or "having" can be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or a combination thereof, but cannot be interpreted as excluding the existence or possibility of addition of one or more other characteristics, numbers, operations, constituent elements, components, or a combination thereof.

[0038] In addition, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0039] In the description of the embodiments of the present application, it should be noted that unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the two are connected and the relative positional relationship after connection remains unchanged. "Rotational connection" means that the two are connected and can rotate relative to each other after connection. "Sliding connection" means that the two are connected and can slide relative to each other after connection. The orientation terms mentioned in the embodiments of the present application, such as "top", "bottom", "inner", "outer", "left", "right", etc., are only references to the directions in the drawings. Therefore, the orientation terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the embodiments of the present application.

[0040] In addition, in the embodiments of the present application, mathematical concepts such as symmetry, equality, parallelism, and perpendicularity are mentioned. These limitations are all in view of the current technological level, rather than absolute strict definitions in the mathematical sense. A small deviation is allowed, and approximate symmetry, approximate equality, approximate parallelism, approximate perpendicularity, etc. are all acceptable. For example, A is parallel to B means that A is parallel to B or approximately parallel to B, and the included angle between A and B can be between 0 degrees and 10 degrees. A is perpendicular to B means that A is perpendicular to B or approximately perpendicular to B, and the included angle between A and B can be between 80 degrees and 100 degrees.

[0041] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A spot shrinking device for an angle-resolved scatterometer, characterized in that: The optical path includes a first lens, a beam shaping element, and a second lens in sequence; Among them, the incident collimated light beam of the angle-resolved scatterometer forms a focused light beam at the focus after passing through the first lens. After passing through the beam shaping element, the focused light beam forms a light beam with a smaller beam diameter and a certain divergence angle. The divergent light beam is collimated and output through the second lens.

2. The spot shrinking device according to claim 1, characterized in that: The beam shaping element is a pinhole stop located at the rear focus of the first lens.

3. The spot shrinking device according to claim 1, characterized in that: The beam shaping element comprises: a speckle elimination element located at the rear focus of the first lens and a pinhole stop located behind the speckle elimination element; Among them, after the focused light beam passes through the speckle elimination element, the speckle is attenuated to form a low-speckle light beam; after the low-speckle light beam passes through the pinhole aperture, it forms a light beam with a smaller beam diameter and a certain divergence angle, and the divergent light beam is collimated by the second lens.

4. The spot shrinking device according to claim 3, characterized in that: The speckle elimination element is composed of a scattering glass sheet and a rotating motor. The scattering glass sheet is perpendicular to the light path. The rotating motor drives the scattering glass sheet to rotate perpendicular to the light path, and the rotation frequency is higher than the sampling frequency of the imaging device.

5. The spot shrinking device according to claim 4, characterized in that: Focus the beam as close as possible to the edge of the scattering glass sheet.

6. The spot shrinking device according to claim 3, characterized in that: The distance between the anti-speckle element and the pinhole aperture is 1mm-2mm.

7. The spot shrinking device according to claim 2 or 3, characterized in that: The pinhole aperture diameter , the focal length of the second lens and the reduced spot diameter Satisfies the following formula: in, is the focal length of the first conjugate lens, is the objective's tube lens focal length, is the focal length of the second conjugate lens, is the magnification of the objective lens, and the first conjugate lens, the objective lens and the second conjugate lens all come from an angle-resolved scatterometer.

8. The spot shrinking device according to claim 2 or 3, characterized in that: The diameter of the reduced light spot does not exceed 5 μm.

9. The spot shrinking device according to claim 2 or 3, characterized in that: The first lens is an achromatic doublet lens.

10. The spot shrinking device according to claim 2 or 3, characterized in that: The distance between the first lens and the collimating lens that forms the incident collimated light beam is the sum of the focal lengths of the first lens and the collimating lens.

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