A spectroscopic ellipsometry system

Abstract

The present application provides a kind of spectral ellipsometry system, comprising: light source, for providing the incident light of polarization state;First reflection projection objective lens, between light source and the optical path between the sample to be measured, for converging the incident light to the surface of the sample to be measured, to form detection spot;Second reflection projection objective lens, symmetrically first reflection projection objective lens is arranged between the optical path between the sample to be measured and spectrometer, for obtaining the reflection light of spot from the surface of the sample to be measured, and collimating processing is carried out to the reflection light;Spectrometer, obtains the reflection light output by second reflection projection objective lens, and carries out the spectrometry about incident angle to the reflection light, to output multiple beam based on partial incident angle spectrometry beam;And at least one detector, obtains multiple beam spectrometry beam output by spectrometer, and determines the film information on the surface of the sample to be measured according to the polarization state parameters of multiple beam spectrometry beam.

Description

Technical Field

[0001] This invention relates to semiconductor measurement equipment, and more specifically to a spectral ellipsometry measurement system. Background Technology

[0002] As semiconductor process nodes continue to shrink, wafer fabrication plants are placing increasingly higher demands on the performance of metrology equipment. Traditional spectral ellipsometry is a non-contact measurement technique used in semiconductor manufacturing to monitor and control the fabrication process of one or more film layers. The key parameters monitored and controlled during this measurement process include film thickness, material refractive index, extinction coefficient, and optical critical dimensions.

[0003] The technical principle of a spectroscopic ellipsometer is mainly based on a polarizer that generates a beam of light with a known polarization state, which is incident on the surface of a sample (e.g., a wafer). The polarization state of the reflected light changes. The spectroscopic ellipsometer then receives the reflected light using a polarizer and a photoelectric conversion device, and processes the polarization state information to invert the information about the film layer. Currently, most commercially available spectroscopic ellipsometer systems, both domestically and internationally, have a single constant optical axis for both the incident and emitted light, with a symmetrically distributed beam of light within a conical angle centered on this axis for incident and received light. According to the Fresnel reflectance calculation formula, different angles of incidence (AOI) will change the polarization state of the emitted light. Since a larger conical angle at which the actual beam is focused onto the wafer results in more inconsistent polarization state information in the emitted light, it is less conducive to algorithm inversion. Conversely, a smaller conical angle leads to a larger spot size focused on the wafer due to diffraction effects. In other words, a large range of beam cone angles on the wafer's angle of incidence (AOI) can easily lead to aliasing of polarization state information of the received light, thus affecting the accuracy of inversion of information such as film thickness and key optical dimensions. However, reducing the beam cone angle makes it impossible to achieve focusing of a smaller spot.

[0004] To address the aforementioned issues, existing technologies employ a split multi-angle receiving optical path architecture, which uses off-axis dual-mirror structures on both the left and right sides of the incident and exit ends to divide the incident angles. However, this architecture leads to uneven polarization state distribution and increases the system's adjustment sensitivity. Moreover, this asymmetrical optical path setup requires different apodized filters for each angle, making its design and engineering implementation relatively complex.

[0005] To address the aforementioned problems in existing technologies, there is an urgent need in the field for a spectral ellipsometric measurement technique capable of splitting the total incident light cone angle into multiple sub-angles and determining the thin film information on the surface of the wafer under test based on these multiple split beams, thereby resolving the contradiction between the spot size and the incident light cone angle. Furthermore, by employing a convex reflector and a concave reflector with a light-passing aperture to form a coaxial reflective projection objective, combined with a symmetrically apertured aperture, this invention can also achieve a uniform distribution of the polarization state of the light, thus eliminating the need for an apodized filter, simplifying the design structure, and reducing the system's assembly sensitivity. Summary of the Invention

[0006] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed descriptions that follow.

[0007] To overcome the aforementioned deficiencies in existing technologies, this invention provides a spectral ellipsometric measurement system capable of splitting the total incident light cone angle into multiple sub-angles and determining the thin film information on the surface of the wafer under test based on these multiple split beams, thereby resolving the contradiction between the spot size and the incident light cone angle. Furthermore, by employing a coaxial reflective projection lens, this spectral ellipsometric measurement system can also achieve a uniform distribution of the polarization state of the light, thus simplifying the design structure and reducing the system's assembly sensitivity.

[0008] Specifically, according to one aspect of the present invention, a spectral ellipsometric measurement system is provided, comprising: a light source for providing incident light in a polarization state; a first reflective projection lens located in the optical path between the light source and the sample to be measured, for converging the incident light onto the surface of the sample to be measured to form a detection spot; a second reflective projection lens symmetrically disposed in the optical path between the sample to be measured and a beam splitter, for acquiring reflected light from the surface of the sample to be measured and collimating the reflected light; a beam splitter for acquiring the reflected light output from the second reflective projection lens and splitting the reflected light with respect to the incident angle to output multiple beams of split beams based on a portion of the incident angle; and at least one detector for acquiring the multiple beams of split beams output by the beam splitter and determining thin film information on the surface of the sample to be measured based on the polarization state parameters of the multiple beams of split beams.

[0009] Optionally, in some embodiments of the invention, the spectral ellipsometric measurement system further includes a polarizer, wherein the polarizer is located between the light source and the first reflective projection lens, and is used to polarize the light beam output from the light source to provide the first reflective projection lens with incident light of the polarization state.

[0010] Optionally, in some embodiments of the invention, the spectral ellipsometric measurement system further includes a polarizer, wherein the polarizer is located between the second reflective projection lens and the beam splitter, and is used to polarize the reflected light output from the second reflective projection lens so as to provide the detector with output light reflecting the change in polarization state via the beam splitter.

[0011] Optionally, in some embodiments of the invention, the spectral ellipsometric measurement system further includes two apodized filters, wherein a first apodized filter is disposed between the polarizer and the first reflective projection lens, and a second apodized filter is disposed between the second reflective projection lens and the beam splitter, and the first apodized filter and the second apodized filter have the same optical parameters.

[0012] Optionally, in some embodiments of the invention, the spectral ellipsometric measurement system further includes a reflective collimation module, which consists of a plane mirror and a spherical mirror and is located between the light source and the polarizer. The reflective collimation module is used to collimate the diverging beam output from the light source and transmit the collimated parallel beam to the polarizer.

[0013] Optionally, in some embodiments of the invention, the reflective projection lens comprises a convex reflector and a concave reflector with a light-transmitting aperture. The incident light passes through the first light-transmitting aperture of the first reflective projection lens, through the first concave reflector, and reaches the first convex reflector. The first convex reflector then diverges and reflects the light back to the first concave reflector, which then converges the light onto the surface of the sample. The reflected light is then converged and reflected by the second concave reflector of the second reflective projection lens to the second convex reflector, where it is collimated and reflected before exiting the second reflective projection lens through the second light-transmitting aperture.

[0014] Optionally, in some embodiments of the invention, the incident light angles of the first concave reflector incident on the surface of the sample under test range from 54.6° to 62° and 72° to 79.4°, respectively, and its numerical aperture is 0.215. The incident light angles of the multiple beams output by the beam splitter are 58.3° and 75.7°, respectively, and the angle range of their separation angle cones is 7.4°, with a corresponding numerical aperture of 0.065. Optionally, in some embodiments of the invention, the distance L between the polarizer and the first projection lens satisfies... Where D is the diameter of the light-transmitting aperture of the first concave mirror, and θ is the angle between the o-ray and e-ray separated by the polarizer.

[0015] Optionally, in some embodiments of the invention, the beam splitter is a beam splitting prism, and the spectral ellipsometric measurement system includes multiple detectors, wherein the beam splitting prism spatially splits the reflected light with respect to the incident angle to output multiple beams based on a portion of the incident angle. The multiple detectors are respectively arranged in multiple light output directions of the beam splitting prism, simultaneously acquiring multiple beams of the beams, and determining the thin film information on the surface of the sample under test based on the polarization state parameters of the multiple beams of the beams.

[0016] Optionally, in some embodiments of the invention, the spectrometer is an aperture diaphragm, and the spectral ellipsometric measurement system includes a detector, wherein the aperture diaphragm rotates to perform time-division of the reflected light with respect to the incident angle, so as to output multiple beams of beams based on a portion of the incident angle, the detector is positioned in one of the light-emitting directions of the aperture diaphragm, acquires multiple beams of beams in a time-division manner, and determines the thin film information of the sample surface based on the polarization state parameters of the multiple beams of beams.

[0017] Optionally, in some embodiments of the invention, the spectrometer is an aperture stop, and the spectral ellipsometric measurement system includes a detector. The aperture stop includes multiple beam-splitting channels that block different incident angles. The aperture stop is displaced, and the reflected light is time-splitting with respect to the incident angle via each beam-splitting channel to output multiple beams based on a portion of the incident angle. The detector is positioned in one of the light-emitting directions of the aperture stop, acquires multiple beams of beams in a time-division manner, and determines the thin film information on the surface of the sample under test based on the polarization state parameters of the multiple beams of beams.

[0018] Optionally, in some embodiments of the invention, the spectral ellipsometry measurement system may further include a drive mechanism for driving the aperture diaphragm wheel to rotate or driving the aperture diaphragm to displace, so as to perform time-separation with respect to the incident angle. Attached Figure Description

[0019] The above-described features and advantages of the present invention will be better understood after reading the following detailed description of embodiments of the present disclosure in conjunction with the accompanying drawings. In the drawings, components are not necessarily drawn to scale, and components having similar related characteristics or features may have the same or similar reference numerals.

[0020] Figure 1 A schematic diagram of a spectral ellipsometric measurement system according to some embodiments of the present invention is shown;

[0021] Figure 2A for Figure 1A schematic diagram of the first reflective projection lens in the spectral ellipsometric measurement system shown.

[0022] Figure 2B for Figure 1 A schematic diagram of the structure of the second reflective projection lens in the spectral ellipsometric measurement system shown.

[0023] Figure 3 for Figure 1 A schematic diagram of the combination of the polarizer and the reflective projection lens in the spectral ellipsometric measurement system shown.

[0024] Figure 4A , 4B A schematic diagram showing the relationship between the length and occlusion ratio of two design architectures of a reflective projection lens in a spectral ellipsometric measurement system provided according to some embodiments of the present invention is shown.

[0025] Figure 5 A schematic diagram is shown of a reflective projection lens in a spectral ellipsometric measurement system provided according to some embodiments of the present invention, showing the acquisition of two incident angles and their corresponding optical cone angles.

[0026] Figure 6 A schematic diagram of the distribution of different incident angles collected by the spectral ellipsometric measurement system provided according to some embodiments of the present invention is shown.

[0027] Figure 7A , 7B A schematic diagram of a spectral ellipsometric measurement system according to other embodiments of the present invention is shown; and

[0028] Figure 8A , 8B A schematic diagram of the aperture diaphragm wheel in a spectral ellipsometric measurement system provided according to other embodiments of the present invention is shown.

[0029] Figure 9 A schematic flowchart of a method for measuring film thickness based on spectral ellipsometric measurement according to some embodiments of the present invention is shown. Attached Figure Description

[0031] 100 and 200 spectral ellipsometry measurement systems;

[0032] 110 light source;

[0033] 121 First reflecting projection lens;

[0034] 122 Second reflective projection lens;

[0035] 1211 First convex reflecting mirror;

[0036] 1221 Second convex reflector;

[0037] 1212 First concave reflecting mirror;

[0038] 1222 Second concave reflector;

[0039] 1210 First light-transmitting aperture;

[0040] 1220 Second light-transmitting aperture;

[0041] 130-diopter prism;

[0042] Detectors 140, 141, and 142;

[0043] 150 polarizer;

[0044] 160 polarizer;

[0045] 170° reflective collimation module;

[0046] 171 plane mirror;

[0047] 172 spherical mirror;

[0048] 181 aperture stop wheel;

[0049] 182 aperture aperture plate;

[0050] The aperture stops of 1811 and 1821 are open at the top and blocked at the bottom;

[0051] The aperture stops of 1812 and 1822 are obscured at the top and open at the bottom;

[0052] A combination of a convex spherical mirror and a concave spherical mirror on a 410 coaxial axis;

[0053] A combination of a 420° coaxial convex ellipsoidal mirror and a concave spherical mirror;

[0054] 411 and 421 combined length curves;

[0055] Working distance curves 412 and 422;

[0056] A. The upper beam;

[0057] B lower beam;

[0058] 10 samples to be tested. Detailed Implementation

[0059] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a thorough understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description.

[0060] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0061] Furthermore, the terms "upper," "lower," "left," "right," "top," "bottom," "horizontal," and "vertical" used in the following description should be understood as the orientations shown in the relevant paragraphs and accompanying drawings. These relative terms are for illustrative purposes only and do not imply that the described apparatus must be manufactured or operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0062] It is understood that although terms such as "first," "second," and "third" may be used herein to describe various components, regions, layers, and / or parts, these components, regions, layers, and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, regions, layers, and / or parts. Therefore, the first components, regions, layers, and / or parts discussed below may be referred to as second components, regions, layers, and / or parts without departing from some embodiments of the present invention.

[0063] As mentioned above, the problem with traditional spectroscopic ellipsometer systems in the prior art is that both the incident and emitted optical axes are single, constant values. According to the incident principle, the spot size (soptsize) ≈ 1.22λ / NA, where λ is the wavelength, NA = n*sinθ, n is the air refractive index, and θ is the beam conic angle. If the beam conic angle has a large range of incident angles (AOI) on the wafer, it can easily lead to aliasing of polarization state information of the received light, thus affecting the inversion accuracy of information such as film thickness and optical critical dimensions. Conversely, if the beam conic angle is reduced, it is impossible to achieve focusing of a smaller spot. Although existing technologies can use a split multi-angle receiving optical path architecture to solve the above problems, this architecture uses off-axis two-mirror structures on both the left and right sides of the incident and emitted ends. On the one hand, this leads to uneven polarization state distribution, and on the other hand, it increases the system's assembly sensitivity. Furthermore, this asymmetrical optical path setting requires different apodized filters for each angle, making the design and engineering implementation relatively complex.

[0064] To address the aforementioned problems in the prior art, this invention provides a spectral ellipsometric measurement system capable of splitting the total incident light cone angle into multiple sub-angles and determining the thin film information on the surface of the wafer under test based on these multiple split beams, thereby resolving the contradiction between the spot size and the incident light cone angle. Furthermore, by employing a convex mirror and a concave mirror with a light-passing aperture to form a coaxial reflective projection lens, combined with a symmetrically apertured aperture, this spectral ellipsometric measurement system can also achieve a uniform distribution of the polarization state of the light, thus eliminating the need for an apodized filter, simplifying the design structure, and reducing the system's assembly sensitivity.

[0065] In some non-limiting embodiments of the present invention, the spectral ellipsometric measurement system mainly includes: a light source for providing incident light with polarization states; a first reflective projection lens located in the optical path between the light source and the sample to be tested for converging the incident light onto the surface of the sample to be tested to form a detection spot; a second reflective projection lens symmetrically disposed in the optical path between the sample to be tested and the beam splitter for acquiring reflected light from the surface of the sample to be tested and collimating the reflected light; a beam splitter for acquiring the reflected light output from the second reflective projection lens and splitting the reflected light with respect to the incident angle to output multiple beams of beams based on a portion of the incident angle; and at least one detector for acquiring the multiple beams of beams output from the beam splitter and determining the thin film information on the surface of the sample to be tested based on the polarization state parameters of the multiple beams of beams.

[0066] Please refer to Figure 1 , Figure 1 A schematic diagram of a spectral ellipsometric measurement system provided according to some embodiments of the present invention is shown.

[0067] like Figure 1 As shown, in some embodiments of the present invention, the spectral ellipsometric measurement system 100 may consist of a light source 110, a reflective collimation module 170, a polarizer 150, a first reflective projection lens 121, a second reflective projection lens 122, a polarizer 160, a beam splitter prism 130, and at least one detector 141, 142.

[0068] Specifically, the light source 110 is used to provide polarized incident light. This incident light can be a wide-band light in the 190nm-2200nm wavelength range, or a wide-band light with a portion of that bandwidth. Commonly used light sources 110 can include halogen lamps, xenon lamps, mercury lamps, mercury-xenon lamps, laser-driven plasma sources (LDLS), multi-color LED combination light sources, etc.

[0069] Furthermore, to shorten the optical path and achieve miniaturization of the entire spectral ellipsometric measurement system 100, a reflective collimation module 170 can preferably be provided between the light source 110 and the polarizer 150. This reflective collimation module 170 can be composed of a spherical mirror 171 and a plane mirror 172. Specifically, the diverging beam output from the light source 110 can first be reflected by the spherical mirror 171 to the plane mirror 172, and then the collimated parallel beam obtained by the plane mirror 172 is transmitted to the polarizer 150. Compared to the lens elements of traditional refractive projection, the reflective collimation module used in this embodiment enables the beam emitted by the light source 110 to be coupled into the polarizer 141 with maximum efficiency, thereby achieving greater light output efficiency and intensity in broadband light projection applications and improving the detection accuracy of thin film information.

[0070] Furthermore, the polarizer 150 can be disposed between the light source 110 and the first reflective projection lens 121. More specifically, the polarizer 150 can also preferably be disposed between the reflective collimation module 170 and the first reflective projection lens 121, for polarizing the parallel beam collimated by the reflective collimation module 170, thereby providing linearly polarized incident light to the reflective projection lens 121.

[0071] Correspondingly, a polarizer 160 can also be provided between the second reflective projection lens 122 and the beam splitter 130 to polarize the reflected light output from the second reflective projection lens 122, so as to provide the detector with output light reflecting the change in polarization state via the beam splitter 130. Here, the polarizer 150 and polarizer 160 in this invention can be Lochtein prisms or GranThompson prisms, which are symmetrically distributed and have consistent polarization parameters. Based on the principle of ellipsometric measurement of film thickness, the polarizer 150 and polarizer 160 can be, but are not limited to, the above two types, and can be filtered by rotating-polarizer ellipsometry (RPE) and rotating-analyzer ellipsometry (RAE).

[0072] In some preferred embodiments, to ensure a uniform distribution of the polarization state of the light, the spectral ellipsometric measurement system 100 may preferably include two apodized filters, i.e., Gaussian asymptotic filters, to further reduce the spot size. Here, the first apodized filter can be positioned between the polarizer 150 and the first reflective projection lens 121, while the second apodized filter can be positioned between the second reflective projection lens 122 and the beam splitter 130. The first and second apodized filters can have a consistent design, for example, having the same optical parameters. Since the spectral ellipsometric measurement system 100 of the present invention uses a symmetrical architecture with coaxial two-reflective projection lenses 121 and 122 for focusing and collimation, compared with the off-axis structure used in the prior art, the present invention no longer needs to design apodized filters with different structures separately, but only needs to set the same apodized filter on the input optical path and the reflected optical path to achieve filtering. Therefore, the design structure is simplified, making its engineering implementation simpler, and the system's assembly and adjustment sensitivity is also lower.

[0073] Optionally, in this invention, at least one of the polarizer 150 and the polarizer 160 can be mounted on a motor that rotates 360° around the optical axis. The polarizer 150 and the polarizer 160 can then rotate relative to each other via the rotation of the motor, and acquire spectral polarization signals. When the motor rotates at an angular velocity ω, the detector 130 can acquire the following periodic modulation signal:

[0074] I(t)=I0·(1+αcos2ωt+βsin2ωt)

[0075] Furthermore, in order to transmit the broadband ultraviolet to near-infrared spectrum of 190nm-2500nm, the materials of polarizer 150 and polarimeter 160 can preferably be magnesium fluoride (MgF2).

[0076] In addition, Figure 1In the illustrated embodiment, the first reflective projection lens 121 and the second reflective projection lens 122 can be symmetrically arranged on both sides of the sample to be tested (e.g., the wafer to be tested) 10. The first reflective projection lens 121 is coaxially arranged in the optical path between the light source 110 and the sample to be tested 10, and is used to converge the incident light onto the surface of the sample to be tested 10 to form a detection spot. The second reflective projection lens 122 is coaxially arranged in the optical path between the sample to be tested 10 and the beam splitter 130, and serves as a reflective receiving lens, used to acquire the reflected light from the surface of the sample to be tested 10 and collimate the reflected light to form parallel light emission. By using coaxial reflective projection lenses 121 and 122, the spectral ellipsometric measurement system 10 can achieve a uniform distribution of the polarization state of the light, thereby simplifying the design structure and reducing the system's assembly sensitivity.

[0077] In this embodiment, the first reflective projection lens 121 and the second reflective projection lens 122 have the same structure and are symmetrically positioned. The structure of the first reflective projection lens 121 will be described in detail below as an example. Please refer to... Figure 2A and Figure 2B , Figure 2A and Figure 2B for Figure 1 The diagram shows the structure of the reflective projection lens in the spectral ellipsometric measurement system.

[0078] like Figure 2A As shown, the first reflective projection lens 121 can be composed of a first convex reflector 1211 and a first concave reflector 1212 with a first light-passing aperture 1210. The polarized incident light emitted from the polarizer 150 first passes through the first concave reflector 1212 via the first light-passing aperture 1210, reaches the first convex reflector 1211 located in front of it, and is then diverged and reflected back to the first concave reflector 1212 by the first convex reflector 1211. Finally, it is converged and reflected by the first concave reflector 1212, thus converging the light to the focal point of the first reflective projection lens 121. Ideally, the light passing through the first reflective projection lens 121 can be converged to the test area on the surface of the sample 10, forming a detection spot of an appropriate size.

[0079] like Figure 2B As shown, the reflected light reflected from the surface of the sample 10 is converged and reflected by the second concave mirror 1222 of the second reflective projection lens 122 to the second convex mirror 1221, and then collimated and reflected by the second convex mirror 12221, so as to be output through the second light aperture 1220 to the second reflective projection lens 122.

[0080] Please refer to further details. Figure 3 , Figure 3 for Figure 1 The diagram shows the structural combination of the polarizer and the first reflective projection lens in the spectral ellipsometric measurement system.

[0081] like Figure 3 As shown, incident light passing through polarizer 150 will generate two refracted rays: an ordinary ray (o-ray) and an extraordinary ray (e-ray). The o-ray perfectly satisfies the law of refraction and propagates within the incident plane, while the e-ray does not satisfy the law of refraction; the ratio of the sine of its incident angle to the sine of its refraction angle is not constant, and it typically does not propagate within the incident plane. To improve stray light suppression, in some embodiments, the present invention can preferably adjust the distance L between polarizer 150 and the first reflective projection lens 121 to... Where D is the diameter of the light-passing aperture 1210 of the concave mirror 1212. The angle between the o-ray and e-ray separated by the polarizer 150. In this way, the first reflective projection lens 121 can ensure that the e-ray emitted from the polarizer 150 does not enter the projection lens 121.

[0082] Those skilled in the art will understand that the above-described method achieves the desired effect by ensuring that the distance L between the polarizer 150 and the projection lens 121 satisfies... The method for suppressing incident stray light is merely a non-limiting implementation provided by the present invention, intended to clearly demonstrate the main concept of the invention and provide a specific solution that is easy for the public to implement, rather than being used to limit the scope of protection of the present invention.

[0083] Furthermore, in this embodiment, the first reflective projection lens 121 can adopt a coaxial two-mirror structure, that is, the two mirrors can be a combination of a coaxial convex spherical mirror and a concave spherical mirror, or a combination of a coaxial convex ellipsoidal mirror and a concave spherical mirror.

[0084] Please refer to the following: Figure 2A , Figure 4A and Figure 4B . Figure 4A The variation trends of the combined length and center occlusion ratio of the coaxial combination of convex and concave spherical mirrors 410 are shown. Figure 4B The variation trends of the combined length and center occlusion ratio of the coaxial combination of a convex ellipsoidal mirror and a concave spherical mirror 420 are shown. Figure 2A and Figure 4A In the diagram, curve 411 represents the change in the combined length of the convex and concave spherical mirror combination 410 with the center obstruction ratio, while curve 412 represents the change in the working distance from the convex spherical mirror 1211 to the focal point of the reflective projection lens 121 with the center obstruction ratio. Correspondingly, in Figure 2A and Figure 4B In the figure, curve 421 represents the change of the combined length of the combination of the convex ellipsoidal mirror and the concave spherical mirror 420 with the central obstruction ratio, while curve 422 represents the change of the working distance from the convex ellipsoidal mirror 1211 to the focal point of the reflective projection lens 121 with the central obstruction ratio.

[0085] The difference between the two types of reflective projection lenses mentioned above lies in the fact that the coaxial combination of a convex spherical mirror and a concave spherical mirror (410) has a looser tolerance sensitivity and is easier to assemble and adjust, while the coaxial combination of a convex ellipsoidal mirror and a concave spherical mirror (420) has a relatively tighter tolerance sensitivity and is more difficult to assemble and adjust. Comparatively, compared to the coaxial combination of a convex ellipsoidal mirror and a concave spherical mirror (410), with the same parameters and a consistent center obstruction ratio, the overall length of the coaxial combination of a convex ellipsoidal mirror and a concave spherical mirror (420) is more compact.

[0086] Please continue reading. Figure 1 In some embodiments of the present invention, the beam splitter 130 can receive collimated and polarized reflected light that has undergone polarization state change processing from the second reflective projection lens 122 and the polarizer 160, and split the reflected light with respect to the incident angle to output multiple beams based on a portion of the incident angle. Then, the beam splitter 130 can output each beam to multiple detectors 141 and 142, respectively, so that they can determine the thin film information on the surface of the sample 10 under test based on the polarization state parameters of the multiple beams.

[0087] Specifically, in Figure 1 In the illustrated embodiment, the beam splitter 130 can be a triangular beam splitter prism, used to spatially split the reflected light from the polarizer 160 with respect to the incident angle, so as to output two beams based on a portion of the incident angle. Detectors 141 and 142 can be spectrometers, respectively positioned in the two output directions of the beam splitter 130, used to simultaneously acquire the two beams and determine the thin film information on the surface of the sample 10 based on the polarization state parameters of the two beams. Compared to implementations that directly use a CCD (Charge-coupled Device) array or a PD (Photo-Diode) array to receive the reflected light, the spectrometer can perform spectral splitting on the received output light, thereby analyzing thin film information such as the material refractive index and extinction coefficient under different wavelengths of detection light, to meet the analysis needs of wide-band light.

[0088] Further, please see Figure 5 and Figure 6 . Figure 5 A schematic diagram is shown of a reflective projection lens in a spectral ellipsometric measurement system provided according to some embodiments of the present invention, showing the acquisition of two incident angles and their corresponding light conic angles. Figure 6 A schematic diagram of the distribution of different incident angles collected by the spectral ellipsometric measurement system provided according to some embodiments of the present invention is shown.

[0089] exist Figure 5 and Figure 6 In the illustrated embodiment, the first reflective projection lens 121 is incident on the surface of the sample 10 at angles θ ranging from 54.6° to 62° and from 72° to 79.4°, with a numerical aperture (NA) of 0.215. The second reflective projection lens 122 uses sub-aperture separation to receive reflected light from the two incident angles and outputs it to a beam splitter prism 130 for spatial beam splitting with respect to the incident angle, outputting two beams with incident angles (AOI) of 54.6° to 62° and 72° to 79.4°. Detectors 142 and 141 can receive these two beams at positions θ1 = 58.3° and θ2 = 75.7° respectively, and determine the thin film information on the surface of the sample 10 based on the polarization state parameters of these two beams. Here, since the incident light maintains an incident angle (AOI) of 24.8°, the spot focused on the sample 10 under test will be controlled to a smaller size, which is beneficial to improving the detection accuracy of the spectral ellipsometric measurement system 100. Furthermore, since the angle range of the separation angle cone of each beam is 7.4°, i.e., NA is 0.065, the consistency of its polarization state information is significantly improved, thus contributing to improving the algorithmic inversion accuracy of information such as film thickness and key optical dimensions.

[0090] Alternatively, please see Figure 7A , 7B And 8A. Figure 7A , 7B A schematic diagram of a spectral ellipsometric measurement system provided according to other embodiments of the present invention is shown. Figure 8A A schematic diagram of the aperture diaphragm wheel in a spectral ellipsometric measurement system provided according to other embodiments of the present invention is shown.

[0091] like Figure 7A , 7B As shown in Figure 8A, in some embodiments of the present invention, the aforementioned beam-splitting prism 130 can be replaced by an aperture stop 181 to perform time-division of the reflected light output from the polarizer 160 with respect to the incident angle. Accordingly, the spectral ellipsometric measurement system 200 in this embodiment only needs to be configured with one detector 140 to acquire multiple beams of light in a time-division manner, and determine the thin film information on the surface of the sample 10 under test based on the polarization state parameters of the multiple beams of light. The remaining structures in the spectral ellipsometric measurement system 200 can refer to the spectral ellipsometric measurement system 100 of the above embodiment, and will not be described again here.

[0092] Specifically, based on Figure 7A , 7B When performing spectral ellipsometric measurement with the spectral ellipsometric measurement system 200 shown in 8A, the incident light with polarization state provided by the light source 110 can be converged onto the surface of the sample 10 to form a detection spot via the first reflective projection lens 121 as described above. The light reflected from the surface of the sample 10 is received and collimated by the symmetrically arranged second reflective projection lens 122 to form parallel light output, and then reaches the aperture wheel 181 after passing through the polarizer 160. The aperture wheel 181 can be rotated by a motor. The upper beam A of the two split beams can be transmitted to the detector 140 along the light output direction through the aperture stop 1811 of the aperture wheel 181, which is open at the top and blocked at the bottom. The lower beam B of the two split beams can be transmitted to the detector 140 along the light output direction through the aperture stop 1812 of the aperture wheel 181, which is blocked at the top and open at the bottom. In this way, the aperture diaphragm 181 can perform time-based beam splitting of the reflected light with respect to the incident angle, thereby outputting multiple beams based on a portion of the incident angle.

[0093] In other words, in this embodiment, the detector 140 can be positioned in one of the light-emitting directions of the aperture diaphragm 181. The aperture diaphragm 181 allows two beams of light to enter the same detector 140 sequentially through its exit aperture, enabling the detector 140 to sample the two beams sequentially. Thus, the detector 140 can acquire multiple beams of light in a time-division multiplexing manner and determine the thin film information on the surface of the sample 10 based on the polarization state parameters of the multiple beams. Furthermore, by employing a symmetrically shaped aperture diaphragm 181 for time-division with respect to the incident angle, this invention can achieve a uniform polarization state distribution, thereby further simplifying the design structure.

[0094] Alternatively, please see Figure 8B . Figure 8B A schematic diagram of the aperture diaphragm wheel in a spectral ellipsometric measurement system provided according to other embodiments of the present invention is shown. Figure 8B In other embodiments shown, the aperture stop wheel 181 can also be replaced by an aperture stop plate 182 driven by a linear motion motor, which switches to the corresponding open / closed aperture stop through a linear cutting-in / cut-out action. Specifically, as Figure 7A and 8B As shown, the upper beam A of the two split beams can be transmitted to the detector 140 along the light output direction through the aperture stop 1821, which is open at the top and blocked at the bottom. Figure 7B and 8B As shown, the lower beam B of the two split beams can be transmitted to the detector 140 along the light output direction through the aperture stop 1822, which is blocked at the top and open at the bottom.

[0095] Comprehensive comparison Figure 1 The spatial spectral ellipsometry measurement system 100 shown, and Figure 7A , 7B The temporal spectral ellipsometry system 200 shown has a higher throughput for reflected light, allowing simultaneous acquisition of two AOI angles, but requires two or more detectors for reception, which places high demands on detector consistency. Conversely, the temporal ellipsometry system 200 has lower throughput for reflected light, requiring two sequential samplings in time, placing higher demands on platform stability, but only requires one detector for reception. From a cost perspective, the temporal ellipsometry system 100 requires more detectors, while the temporal ellipsometry system 200 only needs to add a motion mechanism to control the aperture stop switching. Therefore, in practical applications, the temporal spectral ellipsometry system 200 can be used to optimize costs.

[0096] Furthermore, in the above embodiments of the present invention, since the spectral ellipsometric measurement systems 100 and 200 both use a symmetrical architecture of coaxial two-reflection projection lenses 121 and 122 for focusing and collimation, and the aperture wheel 181's small holes 1811 and 1812 are also symmetrically designed, the beams corresponding to the split sub-apertures are also symmetrical. Therefore, filtering can be achieved simply by setting the same apodized filter on the input optical path and the reflected optical path, thereby simplifying the design structure, making its engineering implementation simpler, and reducing the system's assembly and adjustment sensitivity.

[0097] Furthermore, according to another aspect of the present invention, a method for measuring spectral ellipsometrics is also provided. This method is stored in the memory of a spectral ellipsometric measurement system in the form of computer instructions and executed by a processor connected to the memory, to achieve the function of determining film information such as film thickness, material refractive index, extinction coefficient, and optical critical dimensions on the surface of a semiconductor device based on spectral data from multiple different incident light cone angles.

[0098] Please refer to Figure 9 , Figure 9 A schematic flowchart of a method for measuring film thickness based on spectral ellipsometric measurement according to some embodiments of the present invention is shown.

[0099] like Figure 9As shown, during the spectral ellipsometric measurement process, the processor of the spectral ellipsometric measurement system can first adjust the relative angle between the polarizer 150 and the polarizer 160 to obtain multiple sets of measured spectral data acquired based on different incident angles. Here, these multiple sets of measured spectral data can be acquired based on the above-described spatial spectral dispersive implementation method or based on the above-described temporal spectral dispersive implementation method, and are represented as follows:

[0100]

[0101]

[0102] in, To correspond to the first incident light cone angle First light intensity, Corresponding to the second incident light cone angle The second light intensity, and It is an elliptic variable in spectral data. Elliptic variables , With light intensity The relationship function is given by P, where P is the installation angle of the polarizer 150, A is the installation angle of the polarizer, and AP is the relative angle between the polarizer 150 and the polarizer 160.

[0103] For example, technicians can keep the polarizer angle P constant and change the analyzer angle A to obtain the above multiple sets of results based on different incident angles. The collected measured spectral data.

[0104] For example, technicians can also keep the angle A of the detector constant and change the angle P of the polarizer to obtain the same multiple sets of results based on different incident angles. The collected measured spectral data.

[0105] For example, technicians can also simultaneously change the polarizer angle P and the analyzer angle A to obtain the same multiple sets of results based on different incident angles. The collected measured spectral data.

[0106] Subsequently, the spectral ellipsometric measurement system can substitute the aforementioned multiple sets of measured spectral data acquired based on different incident angles into a pre-established theoretical spectral model to determine the spectral characteristics based on each incident angle. The measured elliptic function values.

[0107] Specifically, the theoretical spectral model based on multiple incident angles can be represented as follows:

[0108]

[0109]

[0110] in, and It is an elliptic variable in spectral data. and These are the relationships between the theoretical elliptic function values ​​and the film thickness parameter (i.e., thickness) in the theoretical spectral models for each incident angle number i.

[0111] The spectral ellipsometry measurement system can first use the above-mentioned multiple sets of measured spectral data acquired based on different incident angles. and Solve to determine the measured spectral parameters and Then, substitute these values ​​into the theoretical spectral model corresponding to the i-th incident angle to calculate the measured ellipsoidal function values ​​for each incident angle i, i.e.:

[0112]

[0113]

[0114] Subsequently, the spectral ellipsometric measurement system can repeatedly change the film thickness parameters of the aforementioned theoretical spectral model (i.e., To obtain multiple theoretical elliptic deflection function values ​​respectively. Then compare it with the corresponding measured elliptic deflection function value. Comparisons and error analyses were performed to determine the spectral fitting error.

[0115] Here, the spectral fitting error can be expressed as follows:

[0116]

[0117] in, , These are for the angle of incidence. and Weights added to the spectrum, M is the number of data points.

[0118] In this way, the spectral ellipsometry measurement system can add weights during the spectral fitting process and reduce errors. When the thickness is less than a preset threshold, the film thickness on the surface of the semiconductor device is determined.

[0119] Furthermore, in some embodiments, since different thin film materials have different Brewster angles, the spectral ellipsometric measurement system can preferably increase the spectral weights close to the Brewster angle of the thin film material to further improve the sensitivity of film thickness measurement.

[0120] Therefore, compared with the existing technology that measures spectral ellipsometrics based on a single constant incident light cone angle, the present invention can selectively increase or decrease the contribution of the spectrum at different incident angles by changing the weights, thus comprehensively adapting to the measurement needs of various thin film materials.

[0121] Furthermore, by constructing a theoretical spectral model for multiple incident angle ranges and correspondingly introducing multiple sets of measured spectral data based on different incident angles, this invention effectively increases the number of fitting points for spectral fitting, thereby reducing fitting error.

[0122] Those skilled in the art will understand that the theoretical spectral model constructed above based on the film thickness parameter is merely a specific embodiment provided by the present invention to meet the needs of film thickness measurement, and is intended to clearly demonstrate the main concept of the present invention, rather than to limit the scope of protection of the present invention.

[0123] Alternatively, in other embodiments, to meet the actual needs of measuring information such as the material refractive index, extinction coefficient, and optical critical dimensions of thin films on the surface of semiconductor devices, those skilled in the art can also establish theoretical spectral models for parameters such as material refractive index, extinction coefficient, and optical critical dimensions, and perform spectral fitting as described above to determine the corresponding thin film information based on the spectral fitting error. These details will not be elaborated further here.

[0124] In summary, the spectral ellipsometric measurement system and method provided by this invention can decompose the total incident light cone angle into multiple sub-angles and determine the thin film information on the surface of the sample under test based on the multiple split beams, thereby resolving the contradiction between the spot size and the incident light cone angle. Furthermore, by using a convex mirror and a concave mirror with a light-passing aperture to form a coaxial reflective projection lens, combined with a symmetrically apertured aperture, this invention can also achieve a uniform distribution of the polarization state of the light, thus eliminating the need for an apodized filter, simplifying the design structure, and reducing the system's assembly sensitivity.

[0125] The prior description of this disclosure is provided to enable any person skilled in the art to make or use this disclosure. Various modifications to this disclosure will be apparent to those skilled in the art, and the general principles defined herein may be applied to other variations without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not intended to be limited to the examples and designs described herein, but should be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A spectral ellipsometric measurement system, characterized in that, include: A light source used to provide incident light in a polarized state; The first reflective projection lens is located in the optical path between the light source and the sample to be tested, and is used to focus the incident light onto the surface of the sample to be tested to form a detection spot. The first reflective projection lens is composed of a first convex reflector and a first concave reflector with a first light-passing hole. The second reflective projection lens is disposed symmetrically to the first reflective projection lens in the optical path between the sample to be tested and the beam splitter. It is used to obtain the reflected light of the light spot from the surface of the sample to be tested and to collimate the reflected light. The second reflective projection lens is composed of a second convex reflector and a second concave reflector with a second light-passing hole. The beam splitter acquires the reflected light output from the second reflective projection lens and splits the reflected light with respect to the incident angle to output multiple beams based on a portion of the incident angle; and At least one detector acquires multiple beams of the split beams output by the beam splitter, and determines the thin film information on the surface of the sample under test based on the polarization state parameters of the multiple beams of the split beams.

2. The spectral ellipsometric measurement system as described in claim 1, characterized in that, It also includes a polarizer, wherein the polarizer is located between the light source and the first reflective projection lens, and is used to polarize the light beam output by the light source so as to provide the polarized incident light to the first reflective projection lens.

3. The spectral ellipsometric measurement system as described in claim 1 or 2, characterized in that, It also includes a polarizer, wherein the polarizer is located between the second reflective projection lens and the beam splitter, and is used to polarize the reflected light output from the second reflective projection lens so as to provide the detector with output light reflecting the change in polarization state via the beam splitter.

4. The spectral ellipsometric measurement system as described in claim 2, characterized in that, It also includes two apodized filters, wherein the first apodized filter is disposed between the polarizer and the first reflective projection lens, and the second apodized filter is disposed between the second reflective projection lens and the beam splitter, and the first apodized filter and the second apodized filter have the same optical parameters.

5. The spectral ellipsometric measurement system as described in claim 2, characterized in that, It also includes a reflective collimation module, which consists of a plane mirror and a spherical mirror and is located between the light source and the polarizer. The reflective collimation module is used to collimate the diverging beam output by the light source and transmit the collimated parallel beam to the polarizer.

6. The spectral ellipsometric measurement system as described in claim 2, characterized in that, The incident light passes through the first light aperture of the first reflective projection lens, through the first concave reflector, and reaches the first convex reflector. It is then diverged and reflected back to the first concave reflector, and finally converged onto the surface of the sample under test by the first concave reflector. The reflected light is converged and reflected by the second concave mirror of the second reflective projection lens to the second convex mirror, and then collimated and reflected by the second convex mirror to be output through the second light aperture to the second reflective projection lens.

7. The spectral ellipsometric measurement system as described in claim 6, characterized in that, The incident light angles of the first concave reflector onto the surface of the sample under test range from 54.6° to 62° and from 72° to 79.4°, respectively, and its numerical aperture is 0.

215. The incident angles of the multiple beams output by the beam splitter are 58.3° and 75.7°, respectively, and the angle range of their separation angle cones is 7.4°, with a corresponding numerical aperture of 0.

065.

8. The spectral ellipsometric measurement system as described in claim 6, characterized in that, The convex reflector is a convex spherical reflector, and the concave reflector is a concave spherical reflector, or... The convex reflector is a convex ellipsoidal reflector, and the concave reflector is a concave spherical reflector.

9. The spectral ellipsometric measurement system as described in claim 6, characterized in that, The distance L between the polarizer and the first reflective projection lens satisfies Where D is the diameter of the light-transmitting aperture of the first concave mirror. The angle between the o-ray and e-ray separated by the polarizer.

10. The spectral ellipsometric measurement system as described in claim 1, characterized in that, The beam splitter is a beam-splitting prism, and the spectral ellipsometric measurement system includes multiple detectors. The beam-splitting prism spatially disperses the reflected light with respect to the incident angle, thereby outputting multiple beams based on a portion of the incident angle. Multiple detectors are respectively positioned in multiple light-emitting directions of the beam splitter to simultaneously acquire multiple beams of the beam splitter, and the thin film information on the surface of the sample under test is determined based on the polarization state parameters of the multiple beams of the beam splitter.

11. The spectral ellipsometric measurement system as described in claim 1, characterized in that, The spectrometer is an aperture stop, and the spectral ellipsometric measurement system includes one of the aforementioned detectors. The aperture diaphragm rotates to perform time-based beam splitting of the reflected light with respect to the incident angle, thereby outputting multiple beams based on a portion of the incident angle. The detector is positioned in one of the light-emitting directions of the aperture diaphragm, acquires multiple beams of the split beams in a time-division manner, and determines the thin film information on the surface of the sample under test based on the polarization state parameters of the multiple beams of the split beams.

12. The spectral ellipsometric measurement system as described in claim 1, characterized in that, The spectrometer is an aperture stop, and the spectral ellipsometric measurement system includes one of the aforementioned detectors. The aperture stop includes multiple beam-splitting channels that block different incident angles. When the aperture stop is displaced, the reflected light is time-splitting with respect to the incident angle via each of the beam-splitting channels to output multiple beams based on a portion of the incident angle. The detector is positioned in one of the light-emitting directions of the aperture stop, acquires multiple beams of the split beams in a time-division manner, and determines the thin film information on the surface of the sample under test based on the polarization state parameters of the multiple beams of the split beams.

13. The spectral ellipsometric measurement system as described in claim 11 or 12, characterized in that, Also includes: A driving mechanism is used to drive the aperture stop wheel to rotate or drive the aperture stop plate to move, so as to perform the time-separation of light with respect to the incident angle.

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