Sample mounting device for elliptical polarization measurement of glass-based film

Abstract

The utility model discloses a sample mounting device for elliptical polarization measurement of a glass-based film, and belongs to the technical field of optical measurement. The device sequentially comprises a thin film, a glass substrate, refractive index matching liquid and a wedge-shaped glass sheet from top to bottom. The glass substrate is plated with a film to form a sample to be measured; the glass substrate and the wedge-shaped glass sheet are combined through the refractive index matching liquid, and gap bubbles are fully removed; the refractive indexes of the refractive index matching liquid, the glass substrate and the wedge-shaped glass sheet are similar, so that the reflectivity of an interface is greatly reduced. According to the sample mounting device provided by the invention, the interference of reflected light on the back surface of the glass substrate during elliptical polarization measurement is greatly reduced, the elliptical polarization parameters of the front surface film can be accurately measured, the subsequent fitting modeling is simple, and the inverted film structure and material parameters are accurate.

Description

Technical Field

[0001] The invention belongs to the technical field of optical measurement, and in particular relates to a sample mounting device for measuring elliptical polarization of a glass-based film. Background Art

[0002] For optical thin films, the film layer usually plays an optical function on a glass substrate. In order to accurately obtain the optical properties of the film, optical measurements are generally performed on thin film products on the same glass substrate to avoid changes in film properties caused by different substrate types. The two sides of the substrate used for measurement are generally parallel, ensuring that the light beam will not be separated after transmission or reflection through the substrate, which is convenient for the overall spectral measurement of the film and substrate. However, this beam characteristic brings problems when performing elliptical polarization (ellipsometry) spectral measurement on a single side of the film. Ellipsometry measurement technology is an important means to invert the thickness and optical properties of the film layer by measuring the polarization properties of the film. For ellipsometry measurement of thin film samples, the front surface is generally coated and the back surface is not coated. The reflected light beam from the back of the substrate will cause the coherence characteristics of the ellipsometric spectrum to weaken, and the source of the polarization characteristics is not unique and inaccurate, which in turn makes it impossible to establish an accurate film fitting model, affecting the calibration of the film structure and optical properties.

[0003] In order to eliminate the problem of inaccurate ellipsometric measurement caused by back reflection of substrate, it is generally necessary to process the back of substrate. The general idea is to perform matte treatment on the back to greatly reduce the proportion of back reflected light entering the polarization measurement detector. Existing practices include rough grinding of the back of substrate, sticking foggy or blackened tape on the back, spraying light-absorbing black paint on the back, etc. Rough grinding and black paint spraying can easily cause irreversible damage to thin film samples, and sticking glue on the back can easily cause strong scattered light, which will also produce strong polarization interference to the polarization measurement of the film surface. These are also the shortcomings faced by the current ellipsometric measurement of glass-based films. Therefore, finding a sample processing method and installation device that can effectively eliminate back reflection interference without introducing new interference and without damaging the sample is the key to further improving the performance of glass-based films and reducing the difficulty of thin film device development. Summary of the invention

[0004] In view of the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a sample mounting device for ellipsometry measurement of glass-based films, which can effectively eliminate the reflected light from the back of the substrate without damaging the sample, thereby overcoming the shortcoming of inaccurate measurement of ellipsometry parameters of glass-based films.

[0005] In order to achieve the above-mentioned purpose, the technical solution proposed by the present invention is:

[0006] A sample mounting device for measuring ellipsometry of a glass-based film is constructed, wherein the structure comprises a film, a glass substrate, a refractive index matching liquid and a wedge-shaped glass sheet in order from top to bottom; the film is a vacuum-plated optical film; the glass substrate is a glass sheet with two parallel and polished surfaces, one side of which is coated with the film, and the other side is not coated, and the non-coated surface is seamlessly combined with the wedge-shaped glass sheet through the refractive index matching liquid; the refractive index matching liquid is a transparent liquid with a refractive index close to that of the glass substrate and the wedge-shaped glass sheet, and can be liquids such as water, ethylene glycol, alcohol, glycerin, cedar oil, and their mutual solutions, which fills the gap between the glass substrate and the wedge-shaped glass sheet and discharges all bubbles in the irradiation area of ​​the measuring light beam; the wedge-shaped glass sheet is a glass sheet with two polished and non-parallel surfaces, and the angle between the two surfaces is 1 to 6 degrees.

[0007] Preferably, the glass substrate is temporarily fixed to the wedge-shaped glass sheet by gravity, adhesive tape or pressure spring sheet.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] 1. No destructive or polluting treatment is required on the sample itself, which facilitates the subsequent processing and use of the film sample;

[0010] 2. The use of refractive index matching liquid can reduce the back reflectivity of the substrate by 1-2 orders of magnitude. Furthermore, by using different liquids to dissolve each other and adjust the refractive index of the matching liquid, the back reflectivity can be reduced to near zero, and the reflectivity interference is smaller than the measurement error of the instrument itself.

[0011] 3. The sample mounting device is self-contained and can be easily integrated with existing commercial ellipsometry equipment, with a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the structure of the sample installation device of the present invention.

[0013] Figure 2 The figure is a schematic diagram of the light path transmission and polarization state in the ellipsometric measurement system of the present invention.

[0014] Figure 3 The figure is a comparison of optical constants of titanium oxide films on a fused quartz wafer and a silicon wafer obtained by ellipsometry measurement according to an embodiment of the present invention.

[0015] Explanation of marks in the figure: 1-film, 2-glass substrate, 3-refractive index matching liquid, 4-wedge-shaped glass plate, 5-ellipsometer sample mounting base, 6-polarizer, 7-analyzer, 8-incident light beam, 9-light beam reflected from the film surface, 10-light beam reflected from the back side of substrate, 11-light beam reflected from the back side of wedge-shaped glass plate, 12-light beam transmitted from the sample, 13-linearly polarized light state before incident on the sample, 14-elliptically polarized light state after reflection from the sample. DETAILED DESCRIPTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings and specific examples.

[0017] A sample mounting device for measuring ellipsometry of a glass-based film, such as Figure 1 As shown, its structure includes a film 1, a glass substrate 2, a refractive index matching liquid 3 and a wedge-shaped glass sheet 4 from top to bottom;

[0018] The film 1 is a vacuum-plated optical film, and its material optical constants and thickness information need to be obtained with the help of ellipsometry measurement method; the glass substrate 2 is a glass sheet with two parallel and polished surfaces, one side of which is coated with the film 1, and the other side is not coated, and the uncoated surface is seamlessly combined with the wedge-shaped glass sheet 4 through a refractive index matching liquid 3; the refractive index matching liquid 3 is a transparent liquid with a refractive index close to that of the glass substrate 2 and the wedge-shaped glass sheet 4, so as to reduce the back reflected light intensity of the glass substrate 2, and can be water, ethylene glycol, alcohol, glycerin, cedar oil and other liquids and their mutual solutions, filling the gap between the glass substrate 2 and the wedge-shaped glass sheet 4, and expelling all bubbles in the measurement light beam irradiation area to prevent bubbles from generating strong reflection and scattering; the wedge-shaped glass sheet 4 is a glass sheet with two polished and non-parallel surfaces, and the angle between the two surfaces is 1 to 6 degrees, so as to offset the back reflected light out of the detector receiving range to avoid generating new polarization interference.

[0019] Preferably, the glass substrate 2 is temporarily fixed to the wedge-shaped glass sheet 4 by gravity, adhesive tape or pressure spring sheet, so as to facilitate the stability of the optical path during the measurement process and the subsequent use of the sample.

[0020] Working principle: The sample mounting device of the present invention is integrally mounted in the optical path of the ellipsometer and placed on the sample mounting base 5 of the ellipsometer. The transmission state of the measuring light beam in the ellipsometer after passing through the polarization element and the sample and the change of the polarization state are shown in the figure. Figure 2 As shown. The monochromatic light beam or laser beam from the monochromator is used as the incident light beam 8, which first passes through the polarizer 6 to form a linear polarized light state 13, and then reflects on the glass-based film, and the polarization state changes to an elliptically polarized light state 14. Then, the polarization state of the elliptically polarized light is detected by the analyzer 7 to determine the accurate polarization state, thereby obtaining the ellipsometric parameters of the sample.

[0021] from Figure 2It can be seen that the reflected light 9 from the surface of the film 1 and the reflected light 10 from the back of the glass substrate 2 can enter the photodetector through the analyzer 7. Before the refractive index matching liquid 3 is filled, the back reflected light 10 has a strong light intensity. After being superimposed with the film reflected light 9, it will cause a significant change in the state of the elliptically polarized light 14, forming polarization interference. After that, it is impossible to obtain the correct film structure and optical parameters through normal modeling and fitting. After the refractive index matching liquid 3 is filled, since the refractive index of the refractive index matching liquid 3 is similar to that of the glass substrate 2 and the wedge-shaped glass sheet 4, an anti-reflection effect can be formed, which greatly reduces the interference of the reflected light from the back of the glass substrate. Similarly, the interface reflected light between the refractive index matching liquid 3 and the wedge-shaped glass sheet 4 is also extremely small and will not cause polarization interference. Due to the existence of the wedge angle, the reflected light 11 from the back of the wedge-shaped glass sheet has a propagation direction that is inconsistent with the film reflected light 9, and will not enter the photodetector, and will not interfere with the ellipsometric measurement of the film.

[0022] Specific example: In order to verify the advantages of the patented technical solution of the present invention, that is, accurate ellipsometric measurement of thin films on transparent glass sheets can be performed without damaging the samples, we used an ellipsometer to measure the optical constants (refractive index and extinction coefficient dispersion curve) of the same titanium oxide thin films on fused quartz substrates and silicon wafers. First, we used atomic layer deposition to prepare the same titanium oxide thin films with a thickness of about 140nm on silicon wafers and fused quartz wafers in the same batch. For silicon wafer-based thin film samples, since the silicon wafer itself is not transparent in the visible and near-infrared bands, and the back side is a non-polished surface with no backlight interference, the traditional method can be used to directly achieve measurement, and then the optical constants of titanium oxide are obtained through modeling and fitting. For fused quartz-based films, we cannot obtain the correct ellipsometric parameters using conventional sample mounting methods. Therefore, based on the technical solution of the present invention, we first used tape to stick the back of the quartz sheet to a wedge-shaped quartz sheet, and then dripped a drop of pure water into the gap between the two quartz sheets. Due to the capillary effect principle, the water droplet naturally filled the gap between the two quartz sheets. After that, press Figure 2 As shown, the sample mounting device is placed on the sample mounting base of the ellipsometer. Finally, the ellipsometer is used to measure the sample, and the ellipsometric parameters related only to the film on the front surface of the quartz substrate can be obtained, and then the optical constants of the titanium oxide film can be obtained by modeling and analysis. The optical constants of titanium oxide on the quartz substrate and silicon wafer are compared, as shown in FIG. Figure 3 As shown, it can be seen that the optical parameters of the titanium oxide materials obtained by the two are basically consistent, which shows the measurement accuracy of the technical solution of the present invention and highlights the non-destructive advantage of the sample.

Claims

1. A sample mounting device for measuring ellipsometry of a glass-based film, characterized in that: The structure of the device includes, from top to bottom, a film, a glass substrate, a refractive index matching liquid and a wedge-shaped glass plate; The film is a vacuum-plated optical film; The glass substrate is a glass sheet with two parallel and polished surfaces, wherein one side of the glass substrate is coated with the film, and the other side is not coated, and the non-coated surface is seamlessly combined with the wedge-shaped glass sheet through a refractive index matching liquid; The refractive index matching liquid is a transparent liquid with a refractive index close to that of the glass substrate and the wedge-shaped glass, which fills the gap between the glass substrate and the wedge-shaped glass and discharges all bubbles in the area irradiated by the measuring light beam; The wedge-shaped glass sheet is a glass sheet with two polished surfaces, two non-parallel surfaces, and an angle between the two surfaces of 1 to 6 degrees.

2. A sample mounting device for measuring ellipsometry of a glass-based film according to claim 1, characterized in that: The glass substrate is temporarily fixed to the wedge-shaped glass sheet by gravity, adhesive tape or pressure spring sheet.

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