Measuring structure and measuring method for optical constant of Ag thin film layer

Abstract

The invention relates to a structure and method for measuring the optical constant of an Ag thin film layer. The measuring structure comprises the Ag thin film layer, a metal buffer layer and a first oxide dielectric layer which are sequentially arranged in a stacked mode. The thickness of the Ag film layer is greater than or equal to 6nm; according to the measurement method, the ellipsometer is adopted to measure the measurement structure. According to the measuring structure provided by the invention, the Ag film layer can be prevented from being oxidized, and the optical constant of the Ag film layer can be relatively accurately obtained by matching with a subsequent measuring method, so that the design and manufacturing of an optical film containing the Ag film layer can be more accurately carried out, and the application thickness lower limit of the Ag film is expanded.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin films, and relates to a measurement structure and a measurement method for optical constants of optical thin films, and in particular to a measurement structure and a measurement method for optical constants of Ag thin film layers. Background Art

[0002] Silver (Ag) thin films are widely used in the field of optical thin films due to their excellent optical properties. Extremely thin Ag films with thicknesses below 15 nm are suitable for applications in a variety of fields, including Low-E and induced transmission filters. However, due to the softness and susceptibility of Ag materials to oxidation, accurate optical constants are difficult to obtain. This is especially true for extremely thin Ag films, which are microscopically discontinuous and differ significantly from those of thicker Ag films or bulk Ag materials.

[0003] Prior art often formulates film stack structures as discrete recipes. However, this approach is not universal and difficult to accurately simulate using thin film design software, making it difficult to optimize the optimal film stack structure. Failure to accurately determine the optical constants of Ag thin films can significantly hinder the design and manufacture of optical thin films. Therefore, there is a need for a structure and method for measuring the optical constants of thin Ag films of relatively low thickness. Summary of the Invention

[0004] The purpose of the present invention is to provide a measurement structure and method for the optical constants of an Ag thin film layer. The measurement structure can prevent the Ag thin film layer from being oxidized. In combination with the subsequent measurement method, the optical constants of the Ag thin film layer can be obtained relatively accurately, so as to more accurately design and manufacture optical films containing Ag thin films, thereby expanding the lower limit of the application thickness of the Ag thin film layer.

[0005] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a structure for measuring the optical constants of an Ag thin film layer, the structure comprising an Ag thin film layer, a metal buffer layer, and a first oxide dielectric layer stacked in sequence;

[0007] The thickness of the Ag thin film layer is ≥6 nm.

[0008] The measurement structure provided by the present invention can prevent the Ag thin film layer from being oxidized. In conjunction with the subsequent measurement method, the optical constants of the Ag thin film layer can be obtained relatively accurately, so as to more accurately design and manufacture the optical thin film of the Ag thin film layer, and also expand the lower limit of the application thickness of the Ag thin film.

[0009] The first oxide dielectric layer protects the Ag thin film layer. To accurately measure the optical constants of the subsequent Ag thin film layer, the deposition rate and thickness of the first oxide dielectric layer must be accurately calculated. This ensures the relative accuracy of its optical constants, and thus the accurate measurement of the optical constants of the Ag thin film layer.

[0010] The metal buffer layer can protect the Ag thin film layer from impact damage, corrosion, and oxidation by the first oxide dielectric layer. In the art, the oxide dielectric layer is made of a hard material, typically harder than the Ag thin film layer, and exhibits a certain degree of oxidizability. The present invention, through the provision of a metal buffer layer, can separate the Ag thin film layer from the first oxide dielectric layer, with minimal impact on the spectrum of the entire measurement structure and minimal impact on the calculation of the optical constants of the Ag thin film layer. Furthermore, the metal buffer layer is relatively gentle during deposition and does not damage the flatness of the Ag thin film layer, thereby ensuring the accuracy of the final measurement.

[0011] The thickness of the Ag thin film layer is ≥6 nm, for example, it can be 6 nm, 8 nm, 10 nm, 12 nm or 15 nm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0012] The “extremely thin” mentioned in the present invention means that the thickness of the Ag thin film layer is ≥ 6 nm.

[0013] In the present invention, if the thickness of the first oxide dielectric layer is too thin, it cannot provide protection. As a preferred technical solution, the thickness of the first oxide dielectric layer is ≥ 8 nm, and can be, for example, 8 nm, 9 nm, 10 nm, 12 nm, 14 nm, 15 nm, 16 nm, or 18 nm, but is not limited to the listed values. Other values within the numerical range not listed are also applicable.

[0014] Preferably, the material of the first oxide dielectric layer includes Al2O3 and / or ZnO.

[0015] In the present invention, the material of the first oxide dielectric layer includes Al2O3 and / or ZnO, which means that the first oxide dielectric layer includes an Al2O3 layer, a ZnO layer, or a composite film layer composed of Al2O3 and ZnO in any proportion.

[0016] Preferably, a second oxide dielectric layer is provided on a side of the Ag thin film layer away from the metal buffer layer.

[0017] The purpose of setting the second oxide dielectric layer of the present invention is to make the Ag film layer flat and oxygen-free. If the substrate itself can provide a flat and oxygen-free environment when the Ag film layer is set, the second oxide dielectric layer may not be set.

[0018] In the present invention, if the thickness of the second oxide dielectric layer is too thin, it cannot provide protection. As a preferred technical solution, the thickness of the second oxide dielectric layer is ≥ 8 nm, and can be, for example, 8 nm, 9 nm, 10 nm, 12 nm, 14 nm, 15 nm, 16 nm, or 18 nm, but is not limited to the listed values. Other values within the numerical range not listed are also applicable.

[0019] Preferably, the material of the second oxide dielectric layer includes Al2O3 and / or ZnO.

[0020] In the present invention, the material of the second oxide dielectric layer includes Al2O3 and / or ZnO, which means that the second oxide dielectric layer includes an Al2O3 layer, a ZnO layer, or a composite film layer composed of Al2O3 and ZnO in any proportion.

[0021] Preferably, the thickness of the metal buffer layer is ≤2 nm, for example, 1 nm, 1.2 nm, 1.5 nm, 1.6 nm, 1.8 nm or 2 nm, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0022] Preferably, the material of the metal buffer layer includes Al and / or Zn.

[0023] The material of the metal buffer layer in the present invention includes Al and / or Zn, which means that the metal buffer layer includes an Al layer, a Zn layer, or a composite film layer composed of Al and Zn in any proportion.

[0024] Preferably, the measurement structure further comprises a substrate arranged on a side of the second oxide dielectric layer away from the Ag thin film layer.

[0025] Preferably, the substrate is made of silicon or glass.

[0026] Illustratively, the method for preparing the measurement structure of the present invention includes: depositing a second oxide dielectric layer, an Ag thin film layer, a metal buffer layer, and a first oxide dielectric layer in sequence on the surface of the base layer.

[0027] The present invention does not further limit the deposition method, as long as the second oxide dielectric layer, Ag thin film layer, metal buffer layer and first oxide dielectric layer of the required thickness can be obtained; illustratively, the deposition is performed using a sputtering coating machine.

[0028] In a second aspect, the present invention provides a method for measuring the optical constants of a Ag thin film, the method comprising the following steps:

[0029] (1) measuring the measurement structure described in the first aspect using an ellipsometer to obtain a measurement file;

[0030] (2) Analyze the measurement file obtained in step (1) to obtain the n value and k value of the Ag thin film layer.

[0031] Preferably, the analysis in step (2) includes: importing the analytical model into the analysis window of the ellipsometer, and then fitting until the value of the root mean square error no longer decreases.

[0032] Preferably, the analytical model includes a stacked Ag thin film layer, a metal buffer layer and a first oxide dielectric layer.

[0033] Further preferably, the analytical model includes a second oxide dielectric layer, an Ag thin film layer, a metal buffer layer and a first oxide dielectric layer that are stacked.

[0034] The materials of the first and second oxide dielectric layers, as well as the optical constants n and k, are known and can be directly imported into the known material library. The Tauc-Lorentz dispersion array model in the general oscillator Gen-Osc is selected, and the initial parameter values of the oscillator are obtained by adjusting the Tauc-Lorentz array parameters to match the known parameters.

[0035] The Gaussian dispersion oscillator model in the general oscillator Gen-Osc is used for the Ag thin film layer, and the Drude model is selected to describe the influence of the free carrier dielectric response.

[0036] The material of the metal buffer layer and the optical constants n and k are known and can be directly imported into the known material library. The Tauc-Lorentz dispersion array model in the general oscillator Gen-Osc is selected, and the initial parameter values of the oscillator are obtained by adjusting the Tauc-Lorentz array parameters to match the known parameters.

[0037] Exemplarily, the fitting includes: inputting an initial thickness into the analytical model and performing a Fit analysis, whereby the oscillator parameters in the analytical model are automatically adjusted to match the actual measurement file; using the root mean square error (MSE) to determine the degree of matching between the fitting data and the measurement data, wherein the smaller the MSE value, the better the matching result between the fitting data and the measurement data; and performing the Fit analysis multiple times until the MSE value no longer decreases.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The measurement structure provided by the present invention can prevent the Ag thin film layer from being oxidized, and can relatively accurately obtain the optical constants of the Ag thin film layer in conjunction with the subsequent measurement method, so as to more accurately design and manufacture optical thin films containing the Ag thin film layer, and also expand the lower limit of the application thickness of the Ag thin film layer; the first metal oxide dielectric layer serves to protect the Ag thin film layer; the metal buffer layer can protect the Ag thin film layer from impact damage and oxides of the first oxide dielectric layer. The present invention can separate the Ag thin film layer from the first oxide dielectric layer by setting the metal buffer layer, and has little effect on the spectrum of the entire measurement structure, and also has little effect on the calculation of the optical constants of the Ag thin film layer; moreover, the metal buffer layer is relatively gentle during deposition and will not damage the flatness of the Ag thin film layer, thereby ensuring the accuracy of the final measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the measurement structure of the optical constants of the Ag thin film layer provided in Example 1;

[0041] Figure 2 An optical constant measurement diagram of the measurement structure provided in Example 1;

[0042] Figure 3 A comparison chart of the measured curve and constructed curve of the Ag thin film layer provided in Example 1;

[0043] Figure 4 Optical constant measurement diagram of the measurement structure provided in Example 2;

[0044] Figure 5 A comparison chart of the measured curve and constructed curve of the Ag thin film layer provided in Example 2;

[0045] Figure 6 Optical constant measurement diagram of the measurement structure provided in Example 3;

[0046] Figure 7 A comparison chart of the measured curve and constructed curve of the Ag thin film layer provided in Example 3;

[0047] Figure 8 Optical constant measurement diagram of the measurement structure provided in Example 4;

[0048] Figure 9 A comparison chart of the measured curve and constructed curve of the Ag thin film layer provided in Example 4;

[0049] Figure 10 Optical constant measurement diagram of the measurement structure provided for Comparative Example 1;

[0050] Figure 11 This is a comparison chart of the measured curve and constructed curve of the Ag thin film layer provided in Comparative Example 1.

[0051] Wherein: 1, second oxide dielectric layer; 2, Ag thin film layer; 3, metal buffer layer; 4, first oxide dielectric layer; 5, substrate. DETAILED DESCRIPTION

[0052] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0053] In order to clearly illustrate the technical solution of the present invention, the model of the ellipsometer in the specific embodiment is JAWOOLLAM-2000VI Ellipsometer, and the above description of the ellipsometer is not regarded as a further limitation of the technical solution of the present invention.

[0054] The film layer structure in the specific embodiment of the present invention is deposited by a reactive sputtering coating machine. This description is only to clearly illustrate the technical solution of the present invention and is not regarded as a further limitation of the technical solution of the present invention.

[0055] Example 1

[0056] This embodiment provides a Figure 1 The measurement structure of the optical constants of the Ag thin film layer shown in the figure comprises a substrate 5, a second oxide dielectric layer 1, an Ag thin film layer 2, a metal buffer layer 3 and a first oxide dielectric layer 4 which are stacked in sequence;

[0057] The substrate 5 is made of Si, polished on one side, with a diameter of 10.16 cm and a thickness of 0.5 mm, and the coating surface is polished;

[0058] The materials and thicknesses of the first oxide dielectric layer 4 , the Ag thin film layer 2 , the metal buffer layer 3 and the second oxide dielectric layer 1 are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] The measurement structure for measuring the optical constants of the Ag thin film layer provided in this embodiment is measured, and the measurement method includes the following steps:

[0063] (1) Use an ellipsometer to measure the measurement structure at multiple angles of 50°, 55°, 60°, 65°, and 70° to obtain measurement files;

[0064] (2) parsing the measurement file obtained in step (1) to obtain the n value and k value of the Ag thin film layer 2;

[0065] The analysis includes: importing an analytical model into an analysis window of an ellipsometer, and then fitting the model until the root mean square error reaches a minimum;

[0066] The fitting includes: inputting an initial thickness into the analytical model and performing a Fit analysis, whereby the oscillator parameters in the analytical model are automatically adjusted to match the actual measurement file; using the root mean square error (MSE) to determine the degree of match between the fitted data and the measured data, wherein the smaller the MSE value, the better the match between the fitted data and the measured data; and performing the Fit analysis multiple times until the MSE value no longer decreases.

[0067] The analytical model includes a second oxide dielectric layer 1, an Ag thin film layer 2, a metal buffer layer 3 and a first oxide dielectric layer 4 which are stacked;

[0068] The materials of the first oxide dielectric layer 4 and the second oxide dielectric layer 1 as well as the optical constants n and k are known and can be directly imported into the known material library. The Tauc-Lorentz dispersion array model in the general oscillator Gen-Osc is selected, and the initial parameter values of the oscillator are obtained by adjusting the Tauc-Lorentz array parameters to match the known parameters.

[0069] The Gaussian dispersion oscillator model in the general oscillator Gen-Osc is used for the Ag thin film layer 2, and the Drude model is selected to describe the influence of the free carrier dielectric response.

[0070] The material of the metal buffer layer 3 and the optical constants n and k are known and can be directly imported into the known material library. The Tauc-Lorentz dispersion array model in the general oscillator Gen-Osc is selected, and the initial parameter values of the oscillator are obtained by adjusting the Tauc-Lorentz array parameters to match the known parameters.

[0071] The optical constant measurement diagram of the measurement structure of the optical constant of the Ag thin film layer provided in this embodiment is as follows: Figure 2 As shown by Figure 2 It can be seen that the refractive index n and the extinction coefficient k increase with the increase of wavelength, which is consistent with the optical characteristics of metal films.

[0072] Agilent Cary-7000 was used to measure the transmittance and reflectance to verify the rationality of the obtained optical constants n and k values: the optical constants of the Ag thin film layer 2, the first oxide dielectric layer 4, the second oxide dielectric layer 1, and the metal buffer layer 3 obtained by ellipsometer fitting calculation were imported into Macleod design software, a thin film design was established for the Ag thin film layer 2 and its optical constants, and reflectance and transmittance curves were constructed. The reflectance and transmittance curves of the measured thin films were used to compare the constructed thin film design curves to check the degree of agreement between the two. Figure 3 It can be seen that the measured curve of the 6 nm Ag thin film layer 2 is highly consistent with the constructed curve, indicating that the optical constants of the Ag thin film layer 2 calculated by the ellipsometer fitting are accurate.

[0073] Example 2

[0074] This embodiment provides a structure for measuring the optical constants of a Ag thin film layer. Except that the thickness of the Ag thin film layer is 8 nm, the rest is the same as that of the embodiment 1.

[0075] The optical constant measurement diagram of the measurement structure of the optical constant of the Ag thin film layer provided in this embodiment is as follows: Figure 4 As shown by Figure 4 It can be seen that the refractive index n and the extinction coefficient k increase with the increase of wavelength, which is consistent with the optical characteristics of metal films.

[0076] Agilent Cary-7000 was used to measure the transmittance and reflectance to verify the rationality of the obtained optical constants n and k values: the optical constants of the Ag thin film layer, the first oxide dielectric layer, the second oxide dielectric layer, and the metal buffer layer obtained by ellipsometer fitting calculation were imported into Macleod design software, a thin film design was established for the Ag thin film layer and its optical constants, and reflectance and transmittance curves were constructed. The reflectance and transmittance curves of the measured thin film were used to compare the constructed thin film design curve to check the degree of agreement between the two. Figure 5 It can be seen that the measured curve of the 8nm Ag thin film layer is highly consistent with the constructed curve, indicating that the optical constants of the Ag thin film layer calculated by the ellipsometer fitting are accurate.

[0077] Example 3

[0078] This embodiment provides a structure for measuring the optical constants of a Ag thin film layer. Except that the thickness of the Ag thin film layer is 10 nm, the rest is the same as that of the embodiment 1.

[0079] The optical constant measurement diagram of the measurement structure of the optical constant of the Ag thin film layer provided in this embodiment is as follows: Figure 6 As shown by Figure 6 It can be seen that the refractive index n and the extinction coefficient k increase with the increase of wavelength, which is consistent with the optical characteristics of metal films.

[0080] Agilent Cary-7000 was used to measure the transmittance and reflectance to verify the rationality of the obtained optical constants n and k values: the optical constants of the Ag thin film layer, the first oxide dielectric layer, the second oxide dielectric layer, and the metal buffer layer obtained by ellipsometer fitting calculation were imported into Macleod design software, a thin film design was established for the Ag thin film layer and its optical constants, and reflectance and transmittance curves were constructed. The reflectance and transmittance curves of the measured thin film were used to compare the constructed thin film design curve to check the degree of agreement between the two. Figure 7 It can be seen that the measured curve of the 10 nm Ag thin film layer is highly consistent with the constructed curve, indicating that the optical constants of the Ag thin film calculated by ellipsometer fitting are accurate.

[0081] Example 4

[0082] This embodiment provides a structure for measuring the optical constants of a Ag thin film layer. Except that the thickness of the Ag thin film layer is 12 nm, the rest is the same as that of the embodiment 1.

[0083] The optical constant measurement diagram of the measurement structure of the optical constant of the Ag thin film layer provided in this embodiment is as follows: Figure 8 As shown by Figure 8 It can be seen that the refractive index n and the extinction coefficient k increase with the increase of wavelength, which is consistent with the optical characteristics of metal films.

[0084] Agilent Cary-7000 was used to measure the transmittance and reflectance to verify the rationality of the obtained optical constants n and k values: the optical constants of the Ag thin film layer, the first oxide dielectric layer, the second oxide dielectric layer, and the metal buffer layer obtained by ellipsometer fitting calculation were imported into Macleod design software, a thin film design was established for the Ag thin film layer and its optical constants, and reflectance and transmittance curves were constructed. The reflectance and transmittance curves of the measured thin film were used to compare the constructed thin film design curve to check the degree of agreement between the two. Figure 9 It can be seen that the measured curve of the 12 nm Ag thin film layer is highly consistent with the constructed curve, indicating that the optical constants of the Ag thin film layer calculated by the ellipsometer fitting are accurate.

[0085] Comparative Example 1

[0086] This comparative example provides a structure for measuring the optical constants of a Ag thin film layer. Except that the thickness of the Ag thin film layer is 4 nm, the rest is the same as that of Example 1.

[0087] The optical constant measurement diagram of the measurement structure of the optical constant of the Ag thin film layer provided in this embodiment is as follows: Figure 10 As shown by Figure 10It can be seen that the refractive index n value and the extinction coefficient k value have jump points as the wavelength increases, and the extinction coefficient K value is negative, indicating that the n and k values obtained by analysis are incorrect.

[0088] Agilent Cary-7000 was used to measure the transmittance and reflectance to verify the rationality of the obtained optical constants n and k values: the optical constants of the Ag thin film layer, the first oxide dielectric layer, the second oxide dielectric layer, and the metal buffer layer obtained by ellipsometer fitting calculation were imported into Macleod design software, a thin film design was established for the Ag thin film layer and its optical constants, and reflectance and transmittance curves were constructed. The reflectance and transmittance curves of the measured thin film were used to compare the constructed thin film design curve to check the degree of agreement between the two. Figure 11 It can be seen that the measured curve of the 4 nm Ag thin film layer has a low degree of agreement with the constructed curve, indicating that the optical constants of the extremely thin Ag film calculated by the ellipsometer fitting are inaccurate.

[0089] In summary, the measurement structure provided by the present invention can prevent the Ag thin film layer from being oxidized, and can relatively accurately obtain the optical constants of the Ag thin film layer in conjunction with the subsequent measurement method, so as to more accurately design and manufacture optical thin films containing the Ag thin film layer, and also expand the lower limit of the application thickness of the Ag thin film layer; the first oxide dielectric layer and the second oxide dielectric layer serve to protect the Ag thin film layer; the metal buffer layer can protect the Ag thin film layer from impact damage and oxidation erosion of the first oxide dielectric layer. The present invention can separate the Ag thin film layer from the first oxide dielectric layer through the provision of the metal buffer layer, and has little effect on the spectrum of the entire measurement structure, and has little effect on the calculation of the optical constants of the Ag thin film layer; moreover, the metal buffer layer is relatively gentle during deposition and will not destroy the flatness of the Ag thin film layer, thereby ensuring the accuracy of the final measurement.

[0090] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A structure for measuring the optical constants of a Ag thin film layer, characterized in that: The measurement structure includes an Ag thin film layer, a metal buffer layer and a first oxide dielectric layer stacked in sequence; The thickness of the Ag thin film layer is ≥6 nm.

2. The measurement structure according to claim 1, characterized in that The thickness of the first oxide dielectric layer is ≥8 nm.

3. The measurement structure according to claim 1 or 2, characterized in that The material of the first oxide dielectric layer includes Al2O3 and / or ZnO.

4. The measurement structure according to any one of claims 1 to 3, characterized in that: A second oxide dielectric layer is provided on the side of the Ag thin film layer away from the metal buffer layer; The thickness of the second oxide dielectric layer is ≥8 nm.

5. The measurement structure according to any one of claims 1 to 4, characterized in that: The material of the second oxide dielectric layer includes Al2O3 and / or ZnO.

6. The measurement structure according to any one of claims 1 to 5, characterized in that: The thickness of the metal buffer layer is less than or equal to 2 nm.

7. The measurement structure according to any one of claims 1 to 6, characterized in that: The material of the metal buffer layer includes Al and / or Zn.

8. The measurement structure according to any one of claims 4 to 7, characterized in that: The measurement structure further includes a substrate disposed on a side of the second oxide dielectric layer away from the Ag thin film layer; Preferably, the substrate is made of silicon or glass.

9. A method for measuring the optical constants of a Ag thin film layer, characterized in that: The measuring method comprises the following steps: (1) measuring the measurement structure according to any one of claims 1 to 8 using an ellipsometer to obtain a measurement file; (2) Analyze the measurement file obtained in step (1) to obtain the n value and k value of the ultra-thin Ag film.

10. The measuring method according to claim 9, characterized in that The analysis in step (2) includes: importing the analytical model into the analysis window of the ellipsometer, and then fitting until the value of the root mean square error no longer decreases.

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