Spectral ellipsometry measurement method, system and storage medium

Abstract

The present invention provides a spectral ellipsometry measurement method, system, and storage medium. The method comprises the following steps: obtaining multiple sets of measured spectral data collected by irradiating a sample to be measured at different incident angles and reflecting the sample to be measured; substituting each set of measured spectral data into a pre-established theoretical spectral model to determine the measured ellipsometric function value based on each incident angle; changing the film thickness parameter of the theoretical spectral model to obtain theoretical ellipsometric function values corresponding to each incident angle and multiple candidate film thicknesses; comparing the theoretical ellipsometric function value for each incident angle with the corresponding measured ellipsometric function value and performing error analysis to determine spectral fitting errors; and determining thin film information on the surface of the sample to be measured based on the spectral fitting errors.

Description

Technical Field

[0001] The present invention relates to semiconductor measurement technology, and in particular to a spectral ellipsometry measurement method, a spectral ellipsometry measurement system, and a computer-readable storage medium. Background Art

[0002] As semiconductor process nodes continue to shrink, wafer fabrication plants are placing increasingly higher demands on metrology equipment. Traditional spectroscopic ellipsometry is a non-contact measurement technique used in semiconductor manufacturing to monitor and control the fabrication process of one or more film layers. 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 spectroscopic ellipsometers is to use a polarizer to generate a beam of light with a known polarization state, which is incident on the surface of a sample (e.g., a wafer). This changes the polarization state of the reflected light. The spectroscopic ellipsometer then receives the reflected light through a polarizer and a photoelectric converter. By processing the polarization state information, the spectroscopic ellipsometer can infer information about the film layer. Currently, most spectroscopic ellipsometer systems on the market, both domestically and internationally, use a single constant value for both the incident and exiting optical axes. With this value as the center of the optical axis, a symmetrically distributed cone angle of light is used for both incident and received light. According to the Fresnel reflectivity calculation formula, different angles of incidence (AOI) will change the polarization state of the exiting light. As the cone angle of the actual beam focused onto the wafer increases, the polarization state information of the exiting light becomes less consistent, making it less conducive to algorithm inversion. Conversely, as the cone angle decreases, the spot size focused on the wafer becomes larger due to diffraction, resulting in a larger diffuse spot. In other words, a wide range of the angle of incidence (AOI) of the beam cone angle on the wafer can easily lead to aliasing of the polarization state information of the received light, thereby affecting the inversion accuracy of information such as film thickness and optical critical dimensions. However, if the beam cone angle is reduced, focusing a smaller spot cannot be achieved.

[0004] To address these issues, existing technologies employ a split multi-angle receiving optical path architecture, employing off-axis dual-mirror objective lenses on both the incident and exit sides to divide the incident angle. However, this architecture can lead to uneven polarization distribution while increasing the system's adjustment sensitivity. Furthermore, this asymmetric optical path configuration requires a different apodization filter for each angle, making its design and engineering implementation relatively complex.

[0005] To address the aforementioned issues in the existing technology, a spectral ellipsometry technique is urgently needed in the field. This technique can split the total incident light cone angle into multiple component angles and determine the thin film information on the wafer surface under test based on these multiple split beams, thereby resolving the conflict between the spot size and the incident light cone angle. Furthermore, by employing a convex reflector and a concave reflector with a light aperture to form a coaxial reflective projection objective lens, combined with a symmetrically opened aperture, the present invention can also achieve a uniform polarization distribution of the light, 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 is a brief summary of one or more aspects to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceivable aspects and is neither intended to identify key or critical 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 description that will be provided later.

[0007] In order to overcome the above-mentioned defects of the prior art, the present invention provides a spectral ellipsometry measurement method, a spectral ellipsometry measurement system, and a computer-readable storage medium, which can split the total incident light cone angle into multiple partial angles, and determine the thin film information on the surface of the wafer to be measured based on multiple split beams, thereby resolving the contradiction between the spot size and the incident light cone angle.

[0008] Specifically, according to one aspect of the present invention, a spectral ellipsometry measurement method is provided, comprising the following steps: obtaining multiple groups of measured spectral data collected by irradiating a sample to be measured at different incident angles and reflecting from the sample to be measured; substituting each group of the measured spectral data into a pre-established theoretical spectral model to respectively determine the measured ellipsometric function value based on each of the incident angles; changing the film thickness parameters of the theoretical spectral model to respectively obtain theoretical ellipsometric function values corresponding to each of the incident angles and multiple candidate film thicknesses; comparing the theoretical ellipsometric function value for each of the incident angles with the corresponding measured ellipsometric function value and performing error analysis to determine the spectral fitting error; and determining the thin film information on the surface of the sample to be measured based on the spectral fitting error.

[0009] Optionally, in some embodiments of the invention, the step of obtaining multiple groups of measured spectral data based on illumination of the sample to be tested at different incident angles and collected through reflection from the sample to be tested includes: converging the incident light of the polarization state provided by the light source onto the surface of the sample to be tested via a first reflective projection objective lens to form a detection light spot, wherein the first reflective projection objective lens is located in the optical path between the light source and the sample to be tested; obtaining reflected light of the light spot from the surface of the sample to be tested via a second reflective projection objective lens, and collimating the reflected light, wherein the second reflective projection objective lens is symmetrically arranged in the optical path between the sample to be tested and a spectrometer with respect to the first reflective projection objective lens; obtaining reflected light output by the second reflective projection objective lens via the spectrometer, and performing spectroscopic processing on the reflected light with respect to the incident angle to output multiple spectroscopic light beams based on part of the incident angles; and

[0010] The multiple split light beams output by the beam splitter are acquired via at least one detector.

[0011] Optionally, in some embodiments of the present invention, the beam splitter is a beam splitter prism. The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing beam splitting on the reflected light with respect to the incident angle to output multiple beams of split light based on a portion of the incident angles includes: performing spatial beam splitting on the reflected light with respect to the incident angles via the beam splitter prism to simultaneously output multiple beams of split light based on a portion of the incident angles. The step of obtaining the multiple split light beams output by the beam splitter via at least one detector includes: simultaneously obtaining the multiple split light beams via multiple detectors arranged at multiple light-emitting directions of the beam splitter prism.

[0012] Optionally, in some embodiments of the invention, the beam splitter is an aperture wheel. The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing beam splitting on the reflected light with respect to the incident angle to output multiple beams of split light based on portions of the incident angle comprises: driving the aperture wheel to rotate, performing temporal beam splitting on the reflected light with respect to the incident angle, and outputting multiple beams of split light based on portions of the incident angle in a time-sharing manner. The step of obtaining the multiple beams of split light output by the beam splitter via at least one detector comprises: obtaining the multiple beams of split light in a time-sharing manner via a detector disposed in one light-emitting direction of the aperture wheel.

[0013] Optionally, in some embodiments of the present invention, the beam splitter is an aperture stop, wherein the aperture stop includes multiple beam splitting channels that block different incident angles. The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing beam splitting on the reflected light with respect to the incident angle to output multiple beams of light based on some of the incident angles includes: driving the aperture stop to shift, performing temporal beam splitting on the reflected light with respect to the incident angle via each of the beam splitting channels, and outputting multiple beams of light based on some of the incident angles in a time-sharing manner. The step of obtaining the multiple beams of light output by the beam splitter via at least one detector includes: obtaining the multiple beams of light in a time-sharing manner via a detector disposed in one light-emitting direction of the aperture stop.

[0014] Optionally, in some embodiments of the invention, the step of obtaining multiple sets of measured spectral data based on different incident angles of illumination of the sample to be tested and collected through reflection from the sample to be tested also includes: based on a first relative angle of a polarizer and a polarizer, respectively obtaining multiple sets of first measured spectral data based on different incident angles, wherein the polarizer is located between the light source and the first reflective projection objective lens, and the polarizer is located between the second reflective projection objective lens and the spectrometer; adjusting the installation angle of the polarizer and / or the polarizer to form a second relative angle; and based on the second relative angle, respectively obtaining multiple sets of second measured spectral data based on different incident angles.

[0015] Optionally, in some embodiments of the invention, the thin film information includes film thickness. The theoretical spectral model is expressed as

[0016] ρ model1 (thickness)=tanψ1*exp(iΔ1)

[0017] ρ model2 (thickness)=tanψ2*exp(iΔ2)

[0018] Among them, ψ1, Δ1, ψ2, and Δ2 are the ellipsometric variables in the spectral data, and ρ model1 (·) and ρ model2 (·) are the relationship functions of the theoretical ellipsometric function value with respect to the film thickness parameter thickness in the theoretical spectrum model of each incident angle number i.

[0019] Optionally, in some embodiments of the invention, the step of substituting each group of the measured spectral data into a pre-established theoretical spectral model to respectively determine the measured ellipsometric function value based on each of the incident angles includes: determining the measured ellipsometric parameters for each of the incident angles based on multiple groups of measured spectral data collected based on different incident angles; and substituting the measured ellipsometric parameters into the theoretical spectral model to respectively determine the measured ellipsometric function value based on each of the incident angles.

[0020]

[0021]

[0022] in, and is the measured ellipsometric parameter θ1 about the first incident angle, and is the measured ellipsometric parameter θ2 about the second incident angle.

[0023] Optionally, in some embodiments of the invention, the step of comparing the theoretical ellipsometric function value for each of the incident angles with the corresponding measured ellipsometric function value and performing error analysis to determine the spectral fitting error includes: determining the corresponding Brewster angle according to the thin film material on the surface of the sample to be tested; determining the spectral weight corresponding to each of the incident angles according to the Brewster angle; and determining the spectral fitting error according to the spectral weight, the theoretical ellipsometric function value for each of the incident angles and its corresponding measured ellipsometric function value.

[0024]

[0025] Among them, w θ1 and w θ2 are the spectral weights corresponding to the incident angles θ1 and θ2, respectively, w θ1 +w θ2 =1, M is the number of data points.

[0026] Optionally, in some embodiments of the invention, the step of determining the thin film information on the surface of the sample to be tested based on the spectral fitting error includes: comparing the spectral fitting error with a preset error threshold; and in response to the comparison result that the spectral fitting error is less than the error threshold, determining the film thickness on the surface of the sample to be tested based on the film thickness parameters of the theoretical spectral model.

[0027] Optionally, in some embodiments of the invention, the thin film information on the surface of the sample to be measured includes at least one of a material refractive index, an extinction coefficient, and a critical dimension of an optical plane.

[0028] Furthermore, the spectroscopic ellipsometry system provided according to the second aspect of the present invention includes a memory and a processor. The memory stores computer instructions. The processor is connected to the memory and configured to execute the computer instructions stored in the memory to implement the spectroscopic ellipsometry method provided by the first aspect of the present invention.

[0029] Furthermore, the computer-readable storage medium provided in the third aspect of the present invention stores computer instructions, which, when executed by a processor, implement the spectroscopic ellipsometry method provided in the first aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above features and advantages of the present invention will be better understood after reading the detailed description of the embodiments of the present disclosure in conjunction with the following drawings. In the drawings, the components are not necessarily drawn to scale, and components with similar related properties or characteristics may have the same or similar reference numerals.

[0031] Figure 1 A schematic structural diagram of a spectroscopic ellipsometry measurement system provided according to some embodiments of the present invention is shown.

[0032] Figure 2A for Figure 1 The structure diagram of the first reflective projection objective lens in the spectroscopic ellipsometric measurement system is shown.

[0033] Figure 2B for Figure 1 The schematic diagram of the structure of the second reflective projection objective lens in the spectroscopic ellipsometric measurement system is shown.

[0034] Figure 3 for Figure 1 Schematic diagram of the structure of the combination between the polarizer and the reflective projection objective lens in the spectroscopic ellipsometric measurement system.

[0035] Figure 4A 、 4B A schematic diagram showing the relationship between two design architecture lengths and shielding ratios of a reflective projection objective lens in a spectroscopic ellipsometric measurement system according to some embodiments of the present invention is shown.

[0036] Figure 5 A schematic diagram illustrating collecting two incident angles and their corresponding light cone angles of a reflective projection objective in a spectroscopic ellipsometric measurement system provided according to some embodiments of the present invention is shown.

[0037] Figure 6 A schematic diagram of the distribution of different incident angles collected by a spectroscopic ellipsometric measurement system according to some embodiments of the present invention is shown.

[0038] Figure 7A、 7B A schematic structural diagram of a spectroscopic ellipsometric measurement system according to some other embodiments of the present invention is shown.

[0039] Figure 8A 、 8B A schematic structural diagram of an aperture stop wheel in a spectroscopic ellipsometric measurement system according to some other embodiments of the present invention is shown.

[0040] Figure 9 A schematic diagram of a process for measuring film thickness based on a spectroscopic ellipsometry method according to some embodiments of the present invention is shown. DETAILED DESCRIPTION

[0041] The following specific embodiments illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this embodiment. On the contrary, the purpose of introducing the invention in conjunction with the embodiment is to cover other options or modifications that may be extended based on the claims of the present invention. In order to provide a deep understanding of the present invention, the following description will include many specific details. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description.

[0042] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0043] Furthermore, the terms "upper," "lower," "left," "right," "top," "bottom," "horizontal," and "vertical" used in the following description should be understood to refer to the orientations depicted in that section and the accompanying drawings. These relative terms are used solely for convenience of description and do not necessarily imply that the devices described herein must be manufactured or operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0044] It will be understood that although the terms "first," "second," "third," etc. may be used herein to describe various components, regions, layers, and / or portions, these components, regions, layers, and / or portions should not be limited by these terms, and these terms are merely used to distinguish different components, regions, layers, and / or portions. Thus, a first component, region, layer, and / or portion discussed below may be referred to as a second component, region, layer, and / or portion without departing from some embodiments of the present invention.

[0045] As mentioned above, a problem with conventional spectroscopic ellipsometer systems in the prior art is that both the incident and exiting optical axes have a single, constant value. Based on the principle of incidence, the spot size (soptsize) is ≈ 1.22λ / NA, where λ is the wavelength, NA is the numerical aperture (NA), n is the refractive index of air, and θ is the light cone angle of the beam. If the light cone angle of the beam falls within a wide range of angles of incidence (AOI) on the wafer, it can easily lead to aliasing of the polarization state information of the received light, thereby affecting the inversion accuracy of information such as film thickness and optical critical dimensions. Conversely, if the light cone angle is reduced, focusing a smaller spot becomes impossible. Although prior art can address this issue using a separate, multi-angle receiving optical path architecture, this architecture employs off-axis, dual-mirror objective lenses on both the left and right sides of the incident and exit ends, which, on the one hand, leads to uneven polarization state distribution, and on the other hand, increases the system's alignment sensitivity. Furthermore, this asymmetric optical path configuration requires a different apodization filter for each angle, making the design and engineering implementation relatively complex.

[0046] To address the aforementioned issues in the prior art, the present invention provides a spectroscopic ellipsometer system that splits the total incident light cone angle into multiple fractional angles and determines thin film information on the wafer surface under test based on these multiple fractional beams, thereby resolving the conflict between spot size and incident light cone angle. Furthermore, by employing a convex reflector and a concave reflector with a light aperture to form a coaxial reflective projection objective, combined with a symmetrical aperture, the spectroscopic ellipsometer system achieves a uniform polarization distribution, eliminating the need for an apodized filter, simplifying the design, and reducing the system's assembly sensitivity.

[0047] In some non-limiting embodiments of the present invention, the spectroscopic ellipsometric measurement system mainly includes: a light source, which is used to provide incident light with a polarization state; a first reflective projection objective lens, which is located in the optical path between the light source and the sample to be measured, and is used to converge the incident light onto the surface of the sample to be measured to form a detection spot; a second reflective projection objective lens, which is symmetrically arranged in the optical path between the sample to be measured and the spectrometer to obtain the reflected light of the spot from the surface of the sample to be measured and to collimate the reflected light; a spectrometer, which obtains the reflected light output by the second reflective projection objective lens and splits the reflected light with respect to the incident angle to output multiple spectroscopic light beams based on partial incident angles; and at least one detector, which obtains the multiple spectroscopic light beams output by the spectrometer and determines the thin film information on the surface of the sample to be measured based on the polarization state parameters of the multiple spectroscopic light beams.

[0048] Please see Figure 1 , Figure 1 A schematic structural diagram of a spectroscopic ellipsometry measurement system provided according to some embodiments of the present invention is shown.

[0049] like Figure 1 As shown, in some embodiments of the present invention, the spectroscopic ellipsometric measurement system 100 may be composed of a light source 110, a reflective collimation module 170, a polarizer 150, a first reflective projection objective lens 121, a second reflective projection objective lens 122, a polarizer 160, a beam splitter prism 130, and at least one detector 141, 142.

[0050] Specifically, light source 110 is used to provide polarized incident light. This incident light can be a broadband light in the 190nm-2200nm band, or a portion thereof. Commonly used light sources 110 include halogen lamps, xenon lamps, mercury lamps, tritium-xenon lamps, laser-driven light sources (LDLS), and multi-color LED combination light sources.

[0051] In addition, in order to shorten the optical path and realize the miniaturization of the entire spectroscopic ellipsometric measurement system 100, a reflective collimation module 170 can be preferably provided between the light source 110 and the polarizer 150. The reflective collimation module 170 can be composed of a spherical reflector 171 and a plane reflector 172. Specifically, the divergent light beam output by the light source 110 can first be reflected by the spherical reflector 171 to the plane reflector 172, and then the parallel light beam obtained after the collimation process is transmitted to the polarizer 150 via the plane reflector 172. Compared with the lens element of the traditional refractive projection, the reflective collimation module adopted in this embodiment can enable the light beam emitted by the light source 110 to be coupled into the polarizer 141 with the greatest efficiency, thereby obtaining greater light extraction efficiency and light intensity in the application of wide-band light projection, thereby improving the detection accuracy of thin film information.

[0052] In addition, the polarizer 150 can be disposed between the light source 110 and the first reflective projection objective lens 121. Furthermore, the polarizer 150 can also be preferably disposed between the reflective collimation module 170 and the first reflective projection objective lens 121 to polarize the parallel light beam collimated by the reflective collimation module 170, thereby providing linearly polarized incident light to the reflective projection objective lens 121.

[0053] Correspondingly, a polarizer 160 may be provided between the second reflective projection objective lens 122 and the beam splitter prism 130 to polarize the reflected light output by the second reflective projection objective lens 122, thereby providing output light reflecting the change in polarization state to the detector via the beam splitter prism 130. The polarizer 150 and polarizer 160 in the present invention may be Rochon prisms or Glan-Thompson prisms, both of which are symmetrically distributed and have consistent polarization parameters. Based on the principle of ellipsometry for film thickness measurement, the polarizer 150 and polarizer 160 include, but are not limited to, the two types described above. They can be used for filtering via rotating-polarizer ellipsometry (RPE) and rotating-analyzer ellipsometry (RAE).

[0054] In some preferred embodiments, to ensure a uniform polarization distribution of the light, the spectroscopic ellipsometer system 100 may also preferably include two apodized filters, i.e., Gaussian progressive filters, to further reduce the spot size. Here, the first apodized filter can be positioned between the polarizer 150 and the first reflective projection objective lens 121, while the second apodized filter can be positioned between the second reflective projection objective lens 122 and the beam splitter 130. The first apodized filter and the second apodized filter can maintain a consistent design, for example, having identical optical parameters. Because the spectroscopic ellipsometer system 100 of the present invention utilizes a symmetrical architecture with two coaxial reflective projection objective lenses 121 and 122 for focusing and collimation, compared to the off-axis architecture employed in the prior art, the present invention eliminates the need for separate apodized filters of different designs. Instead, filtering can be achieved by simply placing identical apodized filters in both the input and reflected light paths. This simplifies the design, simplifies engineering implementation, and reduces system assembly sensitivity.

[0055] Optionally, in the present 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 motor can then rotate the polarizer 150 and the polarizer 160 relative to each other, allowing the spectral polarization signal to be collected. When the motor rotates at an angular velocity ω, the detector 130 can collect the following periodic modulation signal:

[0056] I(t)=I0·(1+αcos2ωt+βsin2ωt)

[0057] Furthermore, in order to transmit a broadband ultraviolet to near-infrared spectrum of 190 nm-2500 nm, the material of the polarizer 150 and the polarizer 160 may preferably be magnesium fluoride (MgF 2 ).

[0058] In addition, Figure 1 In the embodiment shown, the first reflective projection objective lens 121 and the second reflective projection objective lens 122 can be symmetrically arranged on both sides of the sample to be measured (for example, a wafer to be measured) 10. The first reflective projection objective lens 121 is coaxially arranged in the optical path between the light source 110 and the sample to be measured 10, and is used to converge the incident light onto the surface of the sample to be measured 10 to form a detection light spot. The second reflective projection objective lens 122 is coaxially arranged in the optical path between the sample to be measured 10 and the beam splitter prism 130, and serves as a reflective receiving objective lens to obtain the reflected light of the detection light spot from the surface of the sample to be measured 10, and collimate the reflected light to form parallel light output. By adopting coaxial reflective projection objective lenses 121 and 122, the spectral ellipsometric measurement system 10 can make the polarization state distribution of the light uniform, thereby simplifying the design structure and reducing the system's adjustment sensitivity.

[0059] In this embodiment, the first reflective projection objective lens 121 and the second reflective projection objective lens 122 have the same structure and are symmetrically positioned. The structure of the reflective projection objective lens will be described in detail below using the first reflective projection objective lens 121 as an example. Figure 2A and Figure 2B , Figure 2A and Figure 2B for Figure 1 The schematic diagram of the structure of the reflective projection objective lens in the spectroscopic ellipsometric measurement system is shown.

[0060] like Figure 2A As shown, the first reflective projection objective lens 121 can be composed of a first convex reflector 1211 and a first concave reflector 1212 with a first light hole 1210. The polarized incident light emitted from the polarizer 150 first passes through the first light hole 1210 and the first concave reflector 1212 to reach the first convex reflector 1211 located in front of it. The first convex reflector 1211 then undergoes divergent reflection to return to the first concave reflector 1212. The first concave reflector 1212 then undergoes convergent reflection, so that the light converges to the focal point of the first reflective projection objective lens 121. Ideally, the light passing through the first reflective projection objective lens 121 can converge to the test area on the surface of the sample 10 to form a detection spot of an appropriate size.

[0061] like Figure 2B As shown, the reflected light reflected from the surface of the sample 10 to be tested is converged and reflected to the second convex reflector 1221 by the second concave reflector 1222 of the second reflective projection objective lens 122, and then collimated and reflected by the second convex reflector 12221 to output the second reflective projection objective lens 122 through the second light hole 1220.

[0062] Please see further Figure 3 , Figure 3 for Figure 1 The diagram shows the structure of the combination of the polarizer and the first reflective projection objective lens in the spectroscopic ellipsometric measurement system.

[0063] like Figure 3As shown, since the incident light passes through the polarizer 150, two refracted rays are generated, namely the ordinary ray (also called o-ray) and the extraordinary ray (also called e-ray). The o-ray completely 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 the refraction angle is not a constant, and it usually does not propagate within the incident plane. In order to improve the level of stray light suppression, in some embodiments, the present invention can preferably adjust the distance L between the polarizer 150 and the first reflective projection objective lens 121 to L≥D / 2·tanθ, where D is the diameter of the light hole 1210 of the concave reflector 1212, and θ is the angle between the o-ray and the e-ray separated by the polarizer 150. In this way, the first reflective projection objective lens 121 can ensure that the e-ray emitted from the polarizer 150 does not enter the projection objective lens 121.

[0064] Those skilled in the art will understand that the above-mentioned solution of suppressing incident stray light by ensuring that the distance L between the polarizer 150 and the projection objective lens 121 satisfies L≥D / 2·tanθ is only a non-limiting implementation method provided by the present invention, which is intended to clearly demonstrate the main concept of the present invention and provide a specific solution that is easy for the public to implement, rather than to limit the scope of protection of the present invention.

[0065] Furthermore, in this embodiment, the first reflective projection objective lens 121 can adopt a coaxial two-mirror structure, that is, the two reflectors can be a combination of a coaxial convex spherical reflector and a concave spherical reflector, or a combination of a coaxial convex ellipsoidal reflector and a concave spherical reflector.

[0066] Please refer to Figure 2A 、 Figure 4A and Figure 4B . Figure 4A The variation trends of the combined length and the center shielding ratio of the coaxial convex spherical reflector and concave spherical reflector combination 410 are shown. Figure 4B The figure shows the variation trend of the combined length and the center shielding ratio of the coaxial convex ellipsoidal reflector and concave spherical reflector combination 420. Figure 2A and Figure 4A In FIG. 4 , curve 411 shows the variation of the combined length of the convex spherical reflector and the concave spherical reflector combination 410 with the center obscuration ratio, and curve 412 shows the variation of the working distance from the convex spherical reflector 1211 to the focus of the reflective projection objective lens 121 with the center obscuration ratio. Figure 2A and Figure 4B In FIG. 4 , curve 421 represents the variation of the combined length of the convex ellipsoidal reflector and the concave spherical reflector combination 420 with the center obscuration ratio, and curve 422 represents the variation of the working distance from the convex ellipsoidal reflector 1211 to the focus of the reflective projection objective lens 121 with the center obscuration ratio.

[0067] The difference between the two reflective projection objective lenses described above is that the coaxial convex spherical reflector and concave spherical reflector combination 410 has loose tolerances and is relatively easy to assemble and adjust, while the coaxial convex ellipsoidal reflector and concave spherical reflector combination 420 has relatively tight tolerances and is difficult to assemble and adjust. Furthermore, compared to the coaxial convex spherical reflector and concave spherical reflector combination 410, when parameters are identical and the center-to-center obscuration ratio is consistent, the coaxial convex ellipsoidal reflector and concave spherical reflector combination 420 has a more compact overall length.

[0068] Please continue to see Figure 1 In some embodiments of the present invention, the beam splitter prism 130 can receive the collimated and polarized reflected light from the second reflective projection objective lens 122 and the polarizer 160, which has undergone a polarization state change, and split the reflected light according to the incident angle to output multiple split light beams based on portions of the incident angle. The beam splitter prism 130 can then output each split light beam to multiple detectors 141 and 142, respectively, for use in determining thin film information on the surface of the sample 10 to be tested based on the polarization state parameters of the multiple split light beams.

[0069] Specifically, in Figure 1 In the embodiment shown, the beam splitter 130 can be a triangular beam splitter, which is used to perform spatial beam splitting on the reflected light from the polarizer 160 with respect to the incident angle, so as to output two beams of split light based on part of the incident angle. The detectors 141 and 142 can be spectrometers, and are respectively arranged in the two light-emitting directions of the beam splitter 130, so as to simultaneously obtain the two split light beams and determine the thin film information on the surface of the sample 10 to be tested based on the polarization state parameters of the two split light beams. Compared with the implementation method of directly using 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 the thin film information such as the material refractive index and extinction coefficient of the thin film under different wavelengths of detection light, so as to meet the analysis requirements of wide-band light.

[0070] Further, see Figure 5 and Figure 6 . Figure 5 A schematic diagram illustrating collecting two incident angles and their corresponding light cone angles of a reflective projection objective in a spectroscopic ellipsometric measurement system provided according to some embodiments of the present invention is shown. Figure 6 A schematic diagram of the distribution of different incident angles collected by a spectroscopic ellipsometric measurement system according to some embodiments of the present invention is shown.

[0071] exist Figure 5 and Figure 6In the illustrated embodiment, the first reflective projection objective lens 121 receives incident light at an angle θ between 54.6° and 62° and 72° and 79.4°, with a numerical aperture (NA) of 0.215. The second reflective projection objective lens 122 utilizes sub-aperture separation to receive reflected light at two incident angles and outputs the reflected light to the beam splitter prism 130 for spatial separation relative to the incident angle. The resulting two split light beams have angles of incidence (AOIs) of 54.6° to 62° and 72° to 79.4°, respectively. Detectors 142 and 141 receive these two split light beams at positions θ1 = 58.3° and θ2 = 75.7°, respectively, and determine thin film information on the surface of the sample 10 based on the polarization parameters of these two split light beams. Here, because the incident light maintains an angle of incidence (AOI) of 24.8°, the spot focused on the sample 10 is kept small, thereby improving the detection accuracy of the spectroscopic ellipsometric measurement system 100. Furthermore, because the angular range of the separated angle cone of each split beam is 7.4°, i.e., the NA is 0.065, the consistency of its polarization state information is significantly improved, thereby improving the algorithm inversion accuracy of information such as film thickness and optical critical dimensions.

[0072] Alternatively, see Figure 7A 、 7B and 8A. Figure 7A 、 7B A schematic structural diagram of a spectroscopic ellipsometric measurement system according to some other embodiments of the present invention is shown. Figure 8A A schematic structural diagram of an aperture stop wheel in a spectroscopic ellipsometric measurement system according to some other embodiments of the present invention is shown.

[0073] like Figure 7A 、 7B As shown in FIG8A , in some embodiments of the present invention, the beam splitter prism 130 can be replaced with an aperture wheel 181 to perform temporal spectroscopy of the reflected light output by the polarizer 160 with respect to the incident angle. Accordingly, the spectroscopic ellipsometer system 200 in this embodiment requires only one detector 140 to acquire multiple split beams in a time-sharing manner and determine thin film information on the surface of the sample 10 based on the polarization state parameters of these multiple split beams. The remaining structures of the spectroscopic ellipsometer system 200 refer to the spectroscopic ellipsometer system 100 in the aforementioned embodiment and will not be further described here.

[0074] Specifically, based on Figure 7A 、 7BWhen performing spectroscopic ellipsometric measurement using the spectroscopic ellipsometric measurement system 200 shown in FIG8A , the polarized incident light 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 objective lens 121 as described above. Light reflected from the surface of the sample 10 is then received and collimated by the symmetrically arranged second reflective projection objective lens 122 to form parallel light output. The light then passes through the polarizer 160 and reaches the aperture wheel 181. The aperture wheel 181 can be driven to rotate by a motor. The upper beam A of the two split beams can pass through an aperture stop 1811 (open at the top and blocked at the bottom) in the aperture wheel 181, and be transmitted along the light-emitting direction to the detector 140. The lower beam B of the two split beams can pass through an aperture stop 1812 (blocked at the top and open at the bottom) in the aperture wheel 181, and be transmitted along the light-emitting direction to the detector 140. In this way, the aperture wheel 181 can perform temporal separation on the beam of reflected light with respect to the incident angle, thereby outputting a plurality of separated light beams based on partial incident angles.

[0075] That is, in this embodiment, the detector 140 can be positioned in one of the light-emitting directions of the aperture wheel 181. The aperture wheel 181 allows the two beams of light to pass through the light-emitting aperture separately and sequentially into the same detector 140, allowing the detector 140 to sample the two beams sequentially. In this way, the detector 140 can acquire multiple split beams in a time-sharing manner and determine thin film information on the surface of the sample 10 based on the polarization state parameters of the multiple split beams. Furthermore, by employing a symmetrically opened aperture wheel 181 for temporal splitting relative to the incident angle, the present invention can achieve a uniform polarization state distribution, further simplifying the design structure.

[0076] Alternatively, see Figure 8B . Figure 8B Schematic diagram of the structure of the aperture stop wheel in the spectroscopic ellipsometric measurement system provided according to some other embodiments of the present invention is shown. Figure 8B In other embodiments shown, the aperture wheel 181 can also be replaced by an aperture blade 182 driven by a linear motion motor, which switches to the corresponding open or closed aperture through a linear cut-in and cut-out action. Figure 7A and 8B As shown, the upper beam A of the two split beams can pass through the aperture diaphragm 1821 with the upper side open and the lower side blocked in the aperture diaphragm 182 and be transmitted to the detector 140 along the light-emitting direction. 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-emitting direction through the aperture stop 1822 in the aperture stop plate 182, which is blocked at the upper side and opened at the lower side.

[0077] Comprehensive comparison Figure 1 The spectral ellipsometric system 100 based on spatial spectrometry is shown, and Figure 7A 、 7B The spectral ellipsometer measurement system 200 based on time spectroscopy shown in the figure has a higher throughput (throughput) for reflected light than the spectral ellipsometer measurement system 100, and can collect two AOI angles at the same time, but requires two or more detectors for receiving, which also requires high consistency between the detectors. Conversely, the spectral ellipsometer measurement system 200 has a lower throughput (throughput) for reflected light, requires two consecutive samples in time, and has high requirements for the stability of the platform environment, but only requires one detector for receiving. From the perspective of equipment cost, the spectral ellipsometer measurement system 100 requires more detectors, while the spectral ellipsometer measurement system 200 only needs to add a motion mechanism to control the switching of the aperture diaphragm. Therefore, in practical applications, the spectral ellipsometer measurement system 200 based on time spectroscopy can be used to optimize costs.

[0078] Furthermore, in the above-mentioned embodiments of the present invention, since the spectroscopic ellipsometric measurement systems 100 and 200 both adopt a symmetrical structure of two coaxial reflective projection objective lenses 121 and 122 for focusing and collimation, and the pinholes 1811 and 1812 of the above-mentioned aperture stop wheel 181 are also symmetrical in design, the light beams corresponding to the separated sub-apertures are also symmetrical. Therefore, it is only necessary to set the same toe-cut filters on the input light path and the reflected light path to achieve filtering, thereby simplifying the design structure, making its engineering implementation simpler, and the system's adjustment sensitivity is also lower.

[0079] According to another aspect of the present invention, a spectroscopic ellipsometry method is provided. This method, in the form of computer instructions, is stored in the memory of a spectroscopic ellipsometry system and executed by a processor connected to the memory. This method determines film thickness, material refractive index, extinction coefficient, optical critical dimensions, and other film information on the surface of a semiconductor device based on spectral data at multiple different incident light cone angles.

[0080] Please refer to Figure 9 , Figure 9 A schematic diagram of a process for measuring film thickness based on a spectroscopic ellipsometry method according to some embodiments of the present invention is shown.

[0081] like Figure 9 As shown, during the spectroscopic ellipsometric measurement process, the processor of the spectroscopic ellipsometric measurement system can first adjust the relative angle between the polarizer 150 and the polarimeter 160 to obtain multiple sets of measured spectral data collected based on different incident angles. Here, the multiple sets of measured spectral data can be collected based on the above-mentioned spatial spectrometry implementation method or the above-mentioned temporal spectrometry implementation method, and can be expressed as follows:

[0082]

[0083]

[0084] Among them, I(θ1)=f(tanψ1,cosΔ1) is the first light intensity corresponding to the first incident light cone angle θ1, I(θ2)=f(tanψ2,cosΔ2) corresponds to the second light intensity of the second incident light cone angle θ2, ψ and Δ are ellipsometric variables in the spectral data, f(·) is the relationship function between the ellipsometric variables ψ, Δ and the light intensity I, 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.

[0085] For example, technicians can fix the polarizer angle P and change the analyzer angle A to obtain the above multiple groups of polarizations based on different incident angles θ. i The collected measured spectral data.

[0086] For another example, the technician can also fix the angle A of the detector and change the angle P of the polarizer to obtain the above multiple groups of polarizations based on different incident angles θ. i The collected measured spectral data.

[0087] For another example, technicians can also change the polarizer angle P and the analyzer angle A at the same time to obtain the above multiple groups of polarizations based on different incident angles θ i The collected measured spectral data.

[0088] Afterwards, the spectral ellipsometry measurement system can substitute the above-mentioned multiple sets of measured spectral data collected at different incident angles into the pre-established theoretical spectral model to determine the spectral distribution of the incident angle θ. i The measured ellipsometric function value of .

[0089] Specifically, the theoretical spectral model based on various incident angles can be expressed as follows:

[0090] ρ model1 (thickness)=tanψ1*exp(iΔ1),

[0091] ρ model2 (thickness)=tanψ2*exp(iΔ2)

[0092] where ψ and Δ are the ellipsometric variables in the spectral data, and ρ model1 and ρ model2 They are the relationship functions of the theoretical ellipsometric function value with respect to the film thickness parameter (ie, thickness) in the theoretical spectrum model for each incident angle number i.

[0093] The spectral ellipsometric measurement system can first determine the measured ellipsometric parameters (tanψ1, cosΔ1) and (tanψ2, cosΔ2) based on the above-mentioned multiple sets of measured spectral data I(θ1) and I(θ2) collected at different incident angles, and then substitute them into the theoretical spectral model corresponding to the serial number i to calculate the measured ellipsometric function value corresponding to each incident angle serial number i, that is:

[0094]

[0095]

[0096] Afterwards, the spectroscopic ellipsometry measurement system can change the film thickness parameter (i.e., thickness) of the theoretical spectral model multiple times to obtain multiple theoretical ellipsometric function values ρ modeli , and then compare it with the corresponding measured ellipsometric function value ρ measurementi Comparison and error analysis were performed to determine the spectral fitting error.

[0097] Here, the spectrum fitting error can be expressed as follows:

[0098]

[0099] Among them, w θ1 , w θ2 are the weights added to the spectra at incident angles θ1 and θ2, respectively, θ1 +w θ2 =1, and M is the number of data points.

[0100] In this way, the spectroscopic ellipsometry system can add weights in the spectral fitting process and 2 When the value is less than a preset threshold, the thickness of the film layer on the surface of the semiconductor device is determined.

[0101] Furthermore, in some embodiments, since different thin film materials have different Brewster angles, the spectroscopic ellipsometer measurement system may preferably increase the spectral weight close to the Brewster angle of the thin film material to further enhance the sensitivity of film thickness measurement.

[0102] Therefore, compared with the existing technology of spectral ellipsometry measurement based on a single constant incident light cone angle, the present invention can selectively increase or decrease the contribution of spectra at different incident angles by changing the weights, thereby being able to fully adapt to the measurement requirements of various thin film materials.

[0103] In addition, by constructing theoretical spectral models for multiple incident angle ranges and correspondingly introducing multiple sets of measured spectral data based on different incident angles, the present invention also effectively increases the number of fitting points for spectral fitting, thereby reducing the fitting error.

[0104] Those skilled in the art will understand that the above-mentioned theoretical spectral model constructed based on the film thickness parameter (i.e., thickness) is only a specific embodiment provided by the present invention to meet the needs of film thickness measurement, which is intended to clearly demonstrate the main concept of the present invention, and is not used to limit the scope of protection of the present invention.

[0105] Optionally, in other embodiments, to meet the actual needs of measuring the material refractive index, extinction coefficient, optical critical dimensions and other information of the surface film of the semiconductor device, technical personnel in this field can also establish a theoretical spectral model for parameters such as the material refractive index, extinction coefficient, optical critical dimensions, etc., and perform spectral fitting as described above to determine the corresponding film information based on the spectral fitting error, which will not be repeated here.

[0106] In summary, the spectroscopic ellipsometry measurement system and method provided by the present invention can split the total incident light cone angle into multiple component angles and determine thin film information on the surface of the sample to be measured based on the multiple split beams, thereby resolving the conflict between spot size and incident light cone angle. Furthermore, by employing a convex reflector and a concave reflector with a light aperture to form a coaxial reflective projection objective lens, combined with a symmetrically opened aperture, the present invention can also achieve a uniform polarization distribution of the light, eliminating the need for an apodized filter, simplifying the design structure, and reducing the system's adjustment sensitivity.

[0107] The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the 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 the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A spectroscopic ellipsometry method, characterized in that: The following steps are involved: Acquire multiple sets of measured spectral data based on different incident angles of illumination of the sample to be tested and reflected by the sample to be tested; Determining the measured ellipsometric parameters for each incident angle based on each group of measured spectral data; Substitute each set of the measured ellipsometric parameters into a pre-established theoretical spectral model to respectively determine the measured ellipsometric function value based on each incident angle, wherein the theoretical spectral model is expressed as: in, 、 、 、 is the ellipsometric variable in the spectral data, and is the relationship function between the theoretical ellipsometry value and the film thickness parameter thickness in the theoretical spectrum model of each incident angle number i; Changing the film thickness parameter of the theoretical spectral model to obtain theoretical ellipsometric function values corresponding to each of the incident angles and multiple candidate film thicknesses; Determining the Brewster angle corresponding to the thin film material on the surface of the sample to be tested, and determining the spectral weight corresponding to each incident angle accordingly; Determining a spectral fitting error based on the spectral weight, the theoretical ellipsometric function value at each incident angle and its corresponding measured ellipsometric function value; and The thin film information on the surface of the sample to be measured is determined according to the spectrum fitting error, wherein the thin film information includes the film thickness.

2. The spectroscopic ellipsometry method according to claim 1, wherein: The step of obtaining multiple sets of measured spectral data based on different incident angles to illuminate the sample to be tested and reflected by the sample to be tested comprises: Converging the polarized incident light provided by the light source onto the surface of the sample to be measured via a first reflective projection objective lens to form a detection light spot, wherein the first reflective projection objective lens is located in the optical path between the light source and the sample to be measured; Acquire the reflected light of the light spot from the surface of the sample to be measured via a second reflective projection objective lens, and collimate the reflected light, wherein the second reflective projection objective lens is symmetrically arranged in the optical path between the sample to be measured and the beam splitter with respect to the first reflective projection objective lens; Acquire the reflected light output by the second reflective projection objective lens via the beam splitter, and perform beam splitting on the reflected light with respect to an incident angle to output a plurality of split light beams based on some of the incident angles; and The multiple split light beams output by the beam splitter are acquired via at least one detector.

3. The spectroscopic ellipsometry method according to claim 2, wherein: The spectrometer is a spectroscopic prism, wherein: The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing a spatial splitting on the reflected light with respect to the incident angle to output a plurality of split light beams based on a portion of the incident angle comprises: performing a spatial splitting on the reflected light with respect to the incident angle via the beam splitting prism to simultaneously output a plurality of split light beams based on a portion of the incident angle; The step of acquiring the multiple split light beams output by the beam splitter via at least one detector includes: simultaneously acquiring the multiple split light beams via multiple detectors arranged in multiple light-emitting directions of the beam splitter prism.

4. The spectroscopic ellipsometry method according to claim 2, wherein: The optical splitter uses an aperture wheel, wherein: The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing beam splitting on the reflected light with respect to the incident angle to output multiple beams of split light based on parts of the incident angle comprises: driving the aperture wheel to rotate, performing time beam splitting on the reflected light with respect to the incident angle, and outputting multiple beams of split light based on parts of the incident angle in a time-sharing manner; The step of acquiring the multiple split light beams output by the beam splitter via at least one detector includes: acquiring the multiple split light beams in a time-sharing manner via a detector arranged in one light emitting direction of the aperture wheel.

5. The spectroscopic ellipsometry method according to claim 2, wherein: The beam splitter uses an aperture diaphragm, wherein the aperture diaphragm includes multiple beam splitting channels that block different incident angles. The step of obtaining the reflected light output by the second reflective projection objective lens via the beam splitter and performing beam splitting on the reflected light with respect to the incident angle to output multiple beams of split light based on parts of the incident angle comprises: driving the aperture stop to shift, performing time-splitting on the reflected light with respect to the incident angle via each of the beam splitting channels, and outputting multiple beams of split light based on parts of the incident angle in a time-sharing manner; The step of acquiring the multiple split light beams output by the beam splitter via at least one detector includes: acquiring the multiple split light beams in a time-sharing manner via a detector arranged in one light emitting direction of the aperture stop.

6. The spectroscopic ellipsometry method according to claim 2, wherein: The step of obtaining multiple sets of measured spectral data based on different incident angles to illuminate the sample to be tested and reflected by the sample to be tested further includes: Based on a first relative angle between a polarizer and a polarizer, a plurality of sets of first measured spectral data based on different incident angles are respectively acquired, wherein the polarizer is located between the light source and the first reflective projection objective lens, and the polarizer is located between the second reflective projection objective lens and the beam splitter; adjusting the installation angle of the polarizer and / or the polarization analyzer to form a second relative angle; and Based on the second relative angle, multiple groups of second measured spectral data based on different incident angles are respectively acquired.

7. The spectroscopic ellipsometry method according to claim 1, wherein: The step of substituting each group of the measured ellipsometric parameters into a pre-established theoretical spectral model to respectively determine the measured ellipsometric function value based on each incident angle includes: According to the following formula, the measured ellipsometric function value based on each incident angle is determined respectively: in, and is the measured ellipsometric parameter about the first incident angle The measured ellipsometric parameters, and is the measured ellipsometric parameter for the second incident angle The measured ellipsometric parameters.

8. The spectroscopic ellipsometry method according to claim 7, wherein: The step of determining the spectrum fitting error according to the spectrum weight, the theoretical ellipsometer value at each incident angle and its corresponding measured ellipsometer value comprises: The spectrum fitting error is determined according to the following formula: : in, and The corresponding incident angles are and The spectral weight of , M is the number of data points.

9. The spectroscopic ellipsometry method according to claim 1, wherein: The step of determining the thin film information on the surface of the sample to be tested based on the spectrum fitting error includes: Comparing the spectrum fitting error with a preset error threshold; and In response to a comparison result that the spectrum fitting error is less than the error threshold, the film thickness on the surface of the sample to be measured is determined according to the film thickness parameter of the theoretical spectrum model.

10. The spectroscopic ellipsometry method according to claim 1, wherein: The thin film information on the surface of the sample to be measured further includes at least one of a material refractive index, an extinction coefficient, and a critical dimension of an optical plane.

11. A spectroscopic ellipsometry system, characterized in that: include: a memory having computer instructions stored thereon; as well as A processor is connected to the memory and is configured to execute computer instructions stored in the memory to implement the spectroscopic ellipsometry measurement method according to any one of claims 1 to 10.

12. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the computer instructions are executed by a processor, the spectroscopic ellipsometry method according to any one of claims 1 to 10 is implemented.

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