Reflection type film transmittance measuring device

Abstract

The utility model discloses a device for measuring the transmittance of a reflective film. According to the utility model, by adding the reflecting surface, the transmittance of the thin film can be directly calculated through a formula only by respectively measuring the light intensity reflectivity R of the thin film and the light intensity reflectivity R'of the thin film-reflecting surface, and a precise optical model and complex fitting do not need to be established; reflected light of the thin film and light reflected by the reflecting surface do not interfere with each other, amplitude superposition is not involved, only light intensity superposition is achieved, the transmittance can be obtained only by obtaining the light intensity, and the transmittance of the thin film is measured by measuring the reflectivity twice. In the process of measuring the transmittance in a reflection mode, the thickness and the optical property of the film do not need to be known in advance, and the device is very suitable for measuring and monitoring the growth process of the film in situ in real time; all optical elements are arranged on one side of the thin film, the available angle range of incident light is far larger than the angle range of an ellipsometer, and the ellipsometer can be easily integrated with other film manufacturing equipment.

Description

Technical Field

[0001] The utility model relates to an optical film measurement technology, in particular to a device for measuring the transmittance of a reflective film. Background Art

[0002] Thin films are widely used in modern photonics and optoelectronics technologies, including photovoltaics, storage, and chips. They can be used to manufacture a variety of optoelectronic devices, chips, and instruments. Thin film properties, such as material properties, thickness, and uniformity, are crucial to the performance of optoelectronic devices and chips. The optical properties of a material can be characterized by measuring transmittance or absorbance, with different materials exhibiting varying transmittance. Furthermore, real-time, in-situ measurement of the growth of optical thin films allows for investigation of the dynamics of the film-forming process, which is crucial for understanding and optimizing device functionality.

[0003] Optical measurement methods are non-contact, highly accurate, and non-destructive, and are widely used in the measurement and detection of thin film properties in the fields of semiconductors, optical coatings, new energy materials, and the like. Optical measurement methods are mainly divided into two types: reflective and transmissive. Film thickness gauges and ellipsometers based on reflective systems use the principle of thin film interference to measure the reflected light of thin film structures to study the properties of thin films, such as film thickness and the complex refractive index of the material. The transmittance or absorbance of the thin film structure can be further calculated based on the film thickness and the complex refractive index of the material. The physical essence of this reflective system instrument (ellipsometer and film thickness gauge) is to utilize the amplitude superposition interference of many reflected lights at the interface of different materials. To measure the interference spectrum after the film is reflected by a film thickness gauge, one of the parameters, the film thickness and the complex refractive index of the material, must also be known, and the other parameter can be obtained by fitting the interference spectrum through a formula. Although the probe of this film thickness gauge is very small (about 30mm 2 ), which is easy to integrate. However, during the growth of thin film materials, the film thickness and material properties change with time, so the film thickness meter cannot realize real-time in-situ measurement of the film growth process. In addition, for a single-wavelength light source, it is impossible to fit it with a formula, and the film thickness meter cannot obtain the complex refractive index of the material at a single wavelength. The ellipsometer is based on measuring the change in the polarization state of the reflected light of the thin film. It uses precise optical models and complex calculations to simultaneously solve the film thickness and the complex refractive index of the material, and can realize real-time in-situ measurement of the thin film. However, this reflective ellipsometer requires a large oblique light incidence (about 70°), which makes the entire optical system bulky and difficult to integrate.

[0004] Film thickness meters and ellipsometers based on reflection-type systems ignore the transmitted light portion and cannot directly measure the transmittance of the film. Instruments such as spectrophotometers based on transmission-type systems can directly measure the transmittance or absorbance of the film in real time. This transmission-type system requires incident light from one side of the sample and measurement of the transmitted light from the other side of the sample. This transmission-type configuration makes the entire measurement system bulky and difficult to integrate, especially for equipment with a solid object under the sample and requiring extreme temperature changes, such as large-area coaters, spin coaters, vacuum heating / cooling coating equipment [molecular beam epitaxy (MBE) equipment, electron beam evaporation (Ebeam) equipment], etc. In summary, it is still a huge challenge to obtain a method and device that is small in size, easy to integrate, and can measure the transmittance (or absorbance) of a thin film structure in real time and in situ. Summary of the Invention

[0005] In view of the problems in the above prior art that the equipment is large in size, difficult to integrate and cannot measure the properties of the thin film in real time in situ, the utility model proposes a device for measuring the transmittance of a reflective thin film.

[0006] The device for measuring the transmittance of a reflective thin film of the utility model adopts an optical fiber system or a free space optical system.

[0007] The utility model adopts an optical fiber system, and the device for measuring the transmittance of a reflective film includes: a film, a substrate, a light source, an incident optical fiber, an exit optical fiber, a detector or a spectrometer, a computer, and a reflective surface. The film is arranged on a light-transmitting substrate, and the environment is above the film. The light transmittance of the substrate is ≥5%. An incident optical fiber and an exit optical fiber are arranged above the film. The light source is coupled to the incident optical fiber, and the end of the exit optical fiber is coupled to the detector or spectrometer, which is connected to the computer.

[0008] When measuring the light intensity reflectivity of a thin film, a light beam emitted by a light source is incident on the thin film through an incident optical fiber; the incident light is incident on the interface between the environment and the thin film, with part of the light reflected into the environment and part of the light refracted into the thin film; the part of the light refracted into the thin film is reflected and refracted by the interface between the thin film and the substrate; the light reflected at the interface between the thin film and the substrate is reflected back and forth by the upper and lower interfaces of the thin film, and then refracted into the environment and the substrate; the light refracted at the interface between the thin film and the substrate is transmitted from the lower surface of the substrate; the reflected light from the thin film is received by a detector or spectrometer through an output optical fiber. The reflected light from the thin film includes light reflected from the interface between the environment and the thin film to the environment, and light reflected from the interface between the thin film and the substrate and then refracted from the interface between the environment and the thin film to the environment.

[0009] When measuring the transmittance of a thin film, a reflective surface with a known reflectivity is set under the substrate. The amplitude reflectivity of the reflective surface is r0, and the light intensity reflectivity of the reflective surface is R0 = |r0| 2≥5%; the distance from the lower surface of the film to the reflecting surface exceeds the interference length of the light source; the reflecting surface reflects the transmitted light from the lower surface of the substrate back to the substrate, and the light reflected back to the substrate is then transmitted through the film to the environment. The transmitted light passes through the film and substrate twice, and the light transmitted from the substrate to the substrate, reflected by the reflecting surface, and then transmitted through the film to the environment is the light reflected back by the reflecting surface; the reflected light from the film and the light reflected back from the reflecting surface are received by the detector or spectrometer through the output optical fiber; at this time, the light measured by the detector or spectrometer consists of two parts: the reflected light from the film and the light reflected back from the reflecting surface; the thickness of the substrate exceeds the interference length of the light source, and these two parts of light do not interfere.

[0010] Using a free-space optical system, the present invention's reflective film transmittance measurement device includes: a film, a substrate, a light source, a spectrometer, a first lens, a second lens, a detector or a spectrometer, a computer, and a reflective surface; wherein the film is disposed on a light-transmitting substrate, with the environment above the film; the substrate has a light transmittance of ≥5%; the spectrometer, the first lens, and the second lens are disposed above the film; and the detector or spectrometer is connected to the computer.

[0011] When measuring the light intensity reflectivity of a thin film, a light beam emitted by a light source passes through a prism, is collimated by a first lens, and then incident on the thin film through a spectrometer. The incident light is incident on the interface between the environment and the thin film, with part of the light reflected into the environment and part of the light refracted into the thin film. The part of the light refracted into the thin film is reflected and refracted by the interface between the thin film and the substrate. The light reflected at the interface between the thin film and the substrate is reflected back and forth by the upper and lower interfaces of the thin film and then refracted into the environment and the substrate. The light refracted at the interface between the thin film and the substrate is transmitted from the lower surface of the substrate. The reflected light from the thin film passes through the spectrometer, is collected by a second lens, and is coupled to a detector or spectrometer. The reflected light from the thin film includes light reflected from the interface between the environment and the thin film to the environment and light reflected from the interface between the thin film and the substrate and then refracted from the interface between the environment and the thin film to the environment.

[0012] When measuring the transmittance of a thin film, a reflective surface with a known reflectivity is set under the substrate. The amplitude reflectivity of the reflective surface is r0, and the light intensity reflectivity of the reflective surface is R0 = |r0| 2 ≥5%; the distance from the lower surface of the film to the reflecting surface exceeds the interference length of the light source; the reflecting surface reflects the transmitted light from the lower surface of the substrate back to the substrate, and the light reflected back to the substrate is then transmitted through the film to the environment. The transmitted light passes through the film and substrate twice, and the light transmitted from the substrate to the substrate, reflected by the reflecting surface, and then transmitted through the film to the environment is the light reflected back by the reflecting surface; the reflected light of the film and the light reflected back by the reflecting surface pass through the spectrometer together, are collected by the second lens, and are coupled to the detector or spectrometer for reception; at this time, the light measured by the detector or spectrometer consists of two parts: the reflected light of the film and the light reflected back by the reflecting surface, and these two parts of light do not interfere.

[0013] When measuring the light intensity reflectivity of a film, the detector or spectrometer measures the intensity of the reflected light from the film. R , further calculated to obtain the light intensity reflectivity R of the film; when measuring the transmittance of the film, the detector or spectrometer measures the total light intensity I RR , further calculate the light intensity reflectivity R′ of the film-reflecting surface, and then calculate the transmittance T of the film through the measured light intensity reflectivity R of the film and the light intensity reflectivity R′ of the film-reflecting surface.

[0014] The light source uses a multi-wavelength light source to directly measure the transmittance spectrum; or uses a monochromatic light source to measure the transmittance of a single wavelength.

[0015] The distance d between the reflecting surface and the lower surface of the substrate is less than 500 mm.

[0016] The reflective surface adopts a reflective mirror or a reflective film.

[0017] The light splitting element adopts a light splitting prism or a light splitting mirror.

[0018] Furthermore, the present invention includes a moving device, on which the reflective surface is placed. When measuring the light intensity reflectivity of the film, the reflective surface is moved out from under the substrate by the moving device, and no reflective surface is placed under the substrate. When measuring the transmittance of the film, the reflective surface is placed under the substrate by the moving device. The moving device adopts a displacement platform.

[0019] The distance from the bottom surface of the film to the reflecting surface is greater than the interference length of the light source L = λ 2 / (Δλ), λ is the central wavelength of the light source, and Δλ is the spectral width of the light source.

[0020] Advantages of this utility model:

[0021] By adding a reflective surface, the utility model only needs to measure the light intensity reflectivity R of the film and the light intensity reflectivity R′ of the film-reflective surface respectively, and the transmittance of the film can be directly calculated through a formula, without the need to establish a precise optical model and complex fitting; the reflected light of the film and the light reflected back by the reflective surface do not interfere with each other, and do not involve the superposition of amplitudes, only the superposition of light intensities, and only the light intensity needs to be obtained to obtain the transmittance, and the transmittance of the film is measured by the method of measuring the reflectivity twice; in the process of measuring the transmittance using this reflective method, there is no need to know the thickness of the film and the optical properties of the film in advance, which is very suitable for real-time in-situ measurement and monitoring of the growth process of the film; all optical elements of this reflective method are on one side of the film, and the angle θ1 of the incident light satisfies 0°≤θ1<90°, and the angle range is much larger than the angle range of the ellipsometer, which is easy to integrate with other film-making equipment. This device features rapid speed (~ms), simplicity, small size, easy integration, and low cost, and has significant application prospects in optical thin film measurement and real-time monitoring of thin film growth processes. It is particularly advantageous for thin film equipment that is not well-suited to integrated transmission-based devices, such as coaters, spin coaters, MBEs, and Ebeams. Therefore, the device proposed in this invention can be widely used in industrial applications such as semiconductors, optical coatings, and new energy materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of embodiment 1 of the device for measuring transmittance of a reflective thin film according to the present invention;

[0023] Figure 2 Schematic diagram of a second embodiment of a device for measuring transmittance of a reflective thin film according to the present invention;

[0024] Figure 3 A schematic diagram of an embodiment of a device for measuring transmittance of a reflective thin film according to the present invention;

[0025] Figure 4 Result graphs obtained by an embodiment of the device for measuring the transmittance of a reflective film according to the present invention, wherein (a) is a comparison graph of the reflectance or transmittance spectra of the perovskite film experimentally measured without and with a reflective surface using the prior art and the present invention, and (b) is a comparison graph of the light intensity transmittance spectra of the perovskite film calculated using the prior art and the method of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below with reference to specific embodiments with reference to the accompanying drawings.

[0027] Example 1

[0028] In this embodiment, the optical path adopts an optical fiber system.

[0029] like Figure 1As shown, the device for measuring the transmittance of a reflective film in this embodiment includes: a film, a substrate, a light source, an incident optical fiber, an output optical fiber, a spectrometer, a computer, and a reflective surface; wherein the film is arranged on a light-transmitting substrate, and the environment is above the film; the transmittance T of the substrate s ≥5%; an input fiber and an output fiber are placed on the film, bundled together at one end and using a five-axis fiber holder; a light source is connected to one end of the input fiber, and the end of the output fiber is connected to a spectrometer, which is connected to a computer via a data cable; the distance from the bottom surface of the film to the reflective surface exceeds the interference length of the light source. The input and output fibers share a common port, which is secured by a five-axis fiber holder. The five-axis fiber holder adjusts the three-dimensional (xyz) position of the fiber on the film and adjusts the pitch of the fiber to keep it perpendicular to the film surface.

[0030] Example 2

[0031] In this embodiment, the optical path adopts a free space optical system.

[0032] like Figure 2 As shown, the apparatus for measuring the transmittance of a reflective film in this embodiment includes: a film, a substrate, a light source, a first lens, a second lens, a beam splitter, a spectrometer, a computer, and a reflective surface. The film is disposed on a transparent substrate, with the surrounding environment above the film. The incident light is collimated by the first lens, then split and redirected by the beam splitter before being incident on the film. The outgoing light passes through the beam splitter, is reflected by a reflector, and is collected by the second lens and coupled to the spectrometer. The spectrometer is connected to the computer. The beam splitter is partially reflective and partially transmissive.

[0033] The reflective method for real-time in-situ measurement of thin film transmittance of this embodiment includes the following steps:

[0034] a) Setting up the measuring device:

[0035] The film to be measured is placed on a light-transmitting substrate, with the environment above the film; the complex refractive index of the environment is n1, the complex refractive index of the film is n2 (unknown), the thickness is h (unknown), the complex refractive index of the substrate is n3, and the transmittance of the substrate is ≥5%; an input optical fiber and an output optical fiber are placed above the film; a light source is coupled to the input optical fiber, and the end of the output optical fiber is coupled to a spectrometer, and the spectrometer is connected to a computer via a data cable;

[0036] b) Measure the light intensity reflectivity R of the film, such as Figure 3 As shown in the middle left picture:

[0037] 1) The light source emits a light beam, which is incident on the film through the incident optical fiber. The light intensity incident on the film is I0;

[0038] 2) The incident light is incident on the interface between the environment and the film at a first angle θ1. Part of the light is reflected into the environment at the first angle θ1, and part of the light is refracted into the film at a second angle θ2. The first angle θ1 and the second angle θ2 satisfy the refraction law n1sin(θ1)=n2sin(θ2);

[0039] 3) The part of light refracted into the film is reflected and refracted by the interface between the film and the substrate. The reflection angle and refraction angle are the second angle θ2 and the third angle θ3 respectively. The second angle θ2 and the third angle θ3 satisfy the refraction law n1sin(θ1) =

[0040] n2sin(θ2)=n3sin(θ3);

[0041] 4) The light reflected at the interface between the film and the substrate will be reflected back and forth by the upper and lower interfaces of the film, and then refracted into the environment and the substrate; the light refracted at the interface between the film and the substrate is transmitted from the lower surface of the substrate;

[0042] 5) The reflected light from the film is received by the spectrometer through the output optical fiber. The reflected light from the film includes light reflected from the interface between the environment and the film to the environment, and light reflected from the interface between the film and the substrate and then refracted from the interface between the environment and the film to the environment.

[0043] 6) The intensity of the reflected light measured by the spectrometer is I R , and further the light intensity reflectivity of the film is obtained as:

[0044] R=I R / I0 (1);

[0045] c) Measure the light intensity reflectivity R′ of the film-reflecting surface, such as Figure 3 As shown in the middle right picture:

[0046] 1) A reflective surface with known reflectivity is placed under the substrate by a moving device. The amplitude reflectivity of the reflective surface is r0, and the light intensity reflectivity of the reflective surface is R0 = |r0| 2 ≥5%; the distance from the lower surface of the film to the reflecting surface exceeds the interference length of the light source;

[0047] 2) The intensity of the transmitted light on the lower surface of the substrate is I T =I0×T×T s , T is the light transmittance of the film, T s is the light intensity transmittance of the substrate;

[0048] 3) The reflective surface reflects the transmitted light from the lower surface of the substrate back to the substrate. The light reflected back to the substrate is then transmitted through the film to the environment. At this time, the transmitted light passes through the film and substrate twice. The light transmitted from the substrate to the substrate is reflected by the reflective surface and then transmitted through the film to the environment is the intensity I' of the light reflected back by the reflective surface.R for:

[0049] I′ R = I0×T×T s ×R0×T×T s = I0×R0×T 2 ×T s 2 (2)

[0050] 4) Add a reflective surface under the substrate. The reflected light of the film and the light reflected back from the reflective surface are received by the spectrometer through the output optical fiber. The total light intensity measured by the spectrometer is I RR , the light intensity reflectivity R′ of the film-reflecting surface is obtained as:

[0051] R′ = I RR / I0 (3)

[0052] d) Calculate the transmittance T of the film:

[0053] 1) At this time, the light measured by the spectrometer consists of two parts: the reflected light of the film and the light reflected back from the reflective surface. The distance from the lower surface of the film to the reflective surface exceeds the interference length of the light source. These two parts of light do not interfere with each other, but only superposition of intensities, without involving amplitude superposition;

[0054] 2) Add a reflective surface under the substrate, and the total light intensity I measured by the spectrometer RR for:

[0055] I RR = I R + I′ R = I0×R + I0×R0×T 2 ×T s 2 (4)

[0056] 3) The transmittance T of the film is obtained as:

[0057]

[0058] Where R = I R / I0 is the light intensity reflectivity of the film, which has been obtained in step b) 6); R' is the light intensity reflectivity of the film-reflecting surface, which has been obtained in step c) 4); R0 is the light intensity reflectivity of the reflecting surface, which is a known quantity; T s is the transmittance of the substrate, which is a known quantity; we only need to measure the light intensity reflectivity R and the film

[0059] -The light intensity reflectivity R' of the reflecting surface is used to calculate the transmittance of the film using formula (5); when the reflectivity of the reflecting surface and the transmittance of the substrate meet R0 ≥ 95% and T sWhen the transmittance is ≥95%, the transmittance of the film is simplified to T = (R′-R) 1 / 2 The reflected light of the film and the light reflected back by the reflecting surface do not interfere with each other, and there is no superposition of amplitudes, only superposition of light intensities. The transmittance of the film can be directly calculated by measuring the light intensity. During the measurement process, there is no need to know the thickness of the film and the optical properties of the film in advance, so real-time in-situ measurement and monitoring of the film growth process can be achieved.

[0060] In addition, in step a) 5), the complex amplitude reflectivity r of the film satisfies:

[0061]

[0062] Among them, k0 is the vacuum wave vector, r 12 and r 23 are the complex amplitude reflectivity of the interface between the environment and the film and the interface between the film and the substrate, respectively. 12 and t 21 are the complex amplitude transmittances at the interface between the environment and the film and the interface between the film and the substrate, respectively. These quantities can be obtained from the Fresnel formula, and their values ​​are related to the incident angle and the refractive index of the material.

[0063] The first term of formula (6) is the reflection of the incident light by the interface between the environment and the film; the second term is the portion of light in the film that is reflected back and forth by the two interfaces and then refracted into the environment. These two terms interfere with each other to form the interference spectrum of the film. The film thickness measuring instrument based on the thin film interferometry method measures the film thickness by measuring the reflection spectrum based on formula (6). However, this method ignores the transmitted light part E t , the transmission spectrum cannot be measured.

[0064] Figure 4 The following table compares the transmission spectrum of a thin film measured using the optical fiber reflection method of the present invention with the transmission spectrum of a thin film measured using the existing spectrophotometer transmission method. The test sample is a perovskite film with a thickness of about 330nm. The substrate under the perovskite film is glass with a thickness of 1mm, and the distance d between the reflective surface and the lower surface of the substrate is about 50μm. When no reflector is set under the substrate, the reflection spectrum of the perovskite film is measured as follows: Figure 4 The dashed line in the upper figure (a) shows an interference spectrum curve with absorption. When the complex refractive index of the perovskite material is known, the thickness of the film can be obtained by fitting this curve using formula (6). When there is a reflector, the reflection spectrum of the perovskite film-reflector is measured as follows Figure 4 As shown by the short dashed line in the upper middle figure. In the long-wave band (λ>780nm), the perovskite material has little absorption, and a lot of light reaches the reflector below, so the light reflected by the reflector is very strong, resulting in the reflectivity measured by the device being very high in the long-wave band (~80%). The transmission spectrum of perovskite films measured using a transmission type spectrophotometer is currently Figure 4 The solid line indicates the transmission spectrum of the film measured by the optical fiber reflection method of the present invention and the transmission spectrum of the perovskite film measured by the existing spectrophotometer transmission method have basically the same trend in the long-wave band, and the absorption edges basically overlap. The reflection spectrum of the perovskite film-reflector can basically reflect the absorption spectrum of the perovskite film. In the short-wave band (λ<760nm), the perovskite material has strong absorption, and very little light reaches the reflector below, so the effect of the reflector is very small, resulting in the measured light being mainly the light reflected from the upper and lower interfaces of the film, and the reflectivity in the short-wave band is significantly reduced (~20%). There is also interference oscillation. Using formula (6) to fit the interference oscillation spectrum, the film thickness can be measured to be approximately h=320nm, which has a small deviation from the actual thickness of the perovskite [(330-320) / 330≈3%].

[0065] The light transmittance T of the perovskite film is calculated using formula (5), as follows: Figure 4 (b) is shown by the short dashed line. Figure 4 As can be seen in (b), the short dashed line and the transmittance spectrum of the perovskite film measured by the spectrophotometer transmission method (solid line) overlap well, especially in the perovskite absorption edge. The absorbance of the material can be calculated using the formula log(1 / T). The fiber optic reflection type device proposed in this utility model can simultaneously measure the transmittance and film thickness of the perovskite film. The structure shown here is a single-layer film structure, and the transmittance spectrum of a multi-layer film structure can also be measured using the fiber optic reflection type device proposed in this utility model, because the absorption of the multi-layer film is equivalent to the absorption of a single film. This reflective method and device for measuring the transmittance of thin films are used to measure the properties of thin film materials and detect the dynamic processes of the thin film material growth process.

[0066] Finally, it should be noted that the purpose of disclosing the embodiments is to facilitate a further understanding of the present invention. However, those skilled in the art will appreciate that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the contents disclosed in the embodiments; the scope of protection claimed by the present invention shall be determined by the scope defined in the claims.

Claims

1. A device for measuring the transmittance of a reflective thin film, using an optical fiber system, characterized in that: The device for measuring the transmittance of a reflective film comprises: a film, a substrate, a light source, an incident optical fiber, an exit optical fiber, a detector or a spectrometer, a computer, and a reflective surface; wherein the film is disposed on a light-transmitting substrate, with the environment above the film; the light transmittance of the substrate is ≥5%; an incident optical fiber and an exit optical fiber are disposed above the film; the light source is coupled to the incident optical fiber, the end of the exit optical fiber is coupled to the detector or spectrometer, and the detector or spectrometer is connected to the computer; When measuring the light intensity reflectivity of a thin film, a light beam emitted by a light source is incident on the thin film through an incident optical fiber; the incident light is incident on the interface between the environment and the thin film, with part of the light reflected into the environment and part of the light refracted into the thin film; the part of the light refracted into the thin film is reflected and refracted by the interface between the thin film and the substrate; the light reflected at the interface between the thin film and the substrate is reflected back and forth by the upper and lower interfaces of the thin film, and then refracted into the environment and the substrate; the light refracted at the interface between the thin film and the substrate is transmitted from the lower surface of the substrate; the reflected light from the thin film is received by a detector or spectrometer through an output optical fiber. The reflected light from the thin film includes light reflected from the interface between the environment and the thin film to the environment, and light reflected from the interface between the thin film and the substrate and then refracted from the interface between the environment and the thin film to the environment. When measuring the transmittance of a thin film, a reflective surface with a known reflectivity is set under the substrate. The amplitude reflectivity of the reflective surface is r0, and the light intensity reflectivity of the reflective surface is R0 = |r0| 2 ≥5%; the distance from the lower surface of the film to the reflecting surface exceeds the interference length of the light source; the reflecting surface reflects the transmitted light from the lower surface of the substrate back to the substrate, and the light reflected back to the substrate is then transmitted through the film to the environment. The transmitted light passes through the film and substrate twice, and the light transmitted from the substrate to the substrate, reflected by the reflecting surface, and then transmitted through the film to the environment is the light reflected back by the reflecting surface; the reflected light from the film and the light reflected back by the reflecting surface are received by the detector or spectrometer through the output optical fiber; at this time, the light measured by the detector or spectrometer consists of two parts: the reflected light from the film and the light reflected back by the reflecting surface, and these two parts of light do not interfere.

2. A device for measuring the transmittance of a reflective thin film, using a free-space optical system, characterized in that: The device for measuring the transmittance of a reflective film comprises: a film, a substrate, a light source, a spectroscopic element, a first lens, a second lens, a detector or a spectrometer, a computer, and a reflective surface; wherein the film is disposed on a light-transmitting substrate, with the environment above the film; the substrate has a light transmittance of ≥5%; the spectroscopic element, the first lens, and the second lens are disposed above the film; and the detector or the spectrometer is connected to the computer; When measuring the light intensity reflectivity of a thin film, a light beam emitted by a light source passes through a prism, is collimated by a first lens, and then incident on the thin film through a spectrometer. The incident light is incident on the interface between the environment and the thin film, with part of the light reflected into the environment and part of the light refracted into the thin film. The part of the light refracted into the thin film is reflected and refracted by the interface between the thin film and the substrate. The light reflected at the interface between the thin film and the substrate is reflected back and forth by the upper and lower interfaces of the thin film and then refracted into the environment and the substrate. The light refracted at the interface between the thin film and the substrate is transmitted from the lower surface of the substrate. The reflected light from the thin film passes through the spectrometer, is collected by a second lens, and is coupled to a detector or spectrometer. The reflected light from the thin film includes light reflected from the interface between the environment and the thin film to the environment and light reflected from the interface between the thin film and the substrate and then refracted from the interface between the environment and the thin film to the environment. When measuring the transmittance of a thin film, a reflective surface with a known reflectivity is set under the substrate. The amplitude reflectivity of the reflective surface is r0, and the light intensity reflectivity of the reflective surface is R0 = |r0| 2 ≥5%; the distance from the lower surface of the film to the reflecting surface exceeds the interference length of the light source; the reflecting surface reflects the transmitted light from the lower surface of the substrate back to the substrate, and the light reflected back to the substrate is then transmitted through the film to the environment. The transmitted light passes through the film and substrate twice, and the light transmitted from the substrate to the substrate, reflected by the reflecting surface, and then transmitted through the film to the environment is the light reflected back by the reflecting surface; the reflected light of the film and the light reflected back by the reflecting surface pass through the spectrometer together, are collected by the second lens, and are coupled to the detector or spectrometer for reception; at this time, the light measured by the detector or spectrometer consists of two parts: the reflected light of the film and the light reflected back by the reflecting surface; the thickness of the substrate exceeds the interference length of the light source, and these two parts of light do not interfere.

3. The device for measuring transmittance of a reflective thin film according to claim 1 or 2, wherein: The light source is a multi-wavelength light source or a monochromatic light source.

4. The device for measuring transmittance of a reflective thin film according to claim 1 or 2, wherein: The distance between the reflecting surface and the lower surface of the substrate is less than 500 mm.

5. The device for measuring transmittance of a reflective thin film according to claim 1 or 2, wherein: The reflective surface is a reflective mirror or a reflective film.

6. The device for measuring transmittance of a reflective thin film according to claim 1 or 2, wherein: It also includes a moving device, on which the reflecting surface is placed. When measuring the light intensity reflectivity of the film, the reflecting surface is moved out from under the substrate by the moving device. When measuring the transmittance of the film, the reflecting surface is set under the substrate by the moving device.

7. The device for measuring transmittance of a reflective thin film according to claim 1, wherein: A five-axis optical fiber holder is also included. The input optical fiber and the output optical fiber have a common port, and the common port is fixed by the five-axis optical fiber holder.

8. The device for measuring transmittance of a reflective thin film according to claim 2, wherein: The light splitting element is a light splitting prism or a light splitting mirror.

Images