Multi-layer film thickness high-precision measurement system and method based on low-coherence interference

Abstract

The invention relates to a multi-layer film thickness high-precision measurement system and method based on low-coherence interference. According to the system, a low-coherence broadband light source, an optical fiber coupling module and one end of the forked end of a Y-type multimode optical fiber are sequentially and correspondingly arranged, the common end of the Y-type multimode optical fiber, a collimation module and an all-optical-fiber reflection type coaxial probe are sequentially and correspondingly arranged, the other end of the forked end of the Y-type multimode optical fiber is arranged corresponding to a spectrograph, and the spectrograph is connected with a data processing module; the all-fiber reflection type coaxial probe is used for vertically irradiating a collimated light beam to the surface of a tested multi-layer film structure sample and collecting reflected light of the tested multi-layer film structure sample, and the data processing module is used for carrying out Fourier transform on spectral data of the spectrograph and separating out optical path difference signals of all interfaces; and calculating the thickness information of the thin film in the measured multi-layer thin film structure sample. The structure is simple, the cost is low, rapid measurement can be achieved, the data analysis difficulty is low, and the thickness measurement accuracy and stability are high.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of thin film thickness measurement, and particularly relates to a multi-layer thin film thickness high-precision measurement system and method based on low-coherence interference. BACKGROUND

[0002] With the continuous development of optoelectronics, biosensing, display technology and advanced packaging, the application of multi-layer thin film structure is increasingly widespread. Film thickness is a key parameter affecting device performance, directly determining its optical performance, such as transmittance, reflectance, dispersion characteristics and response speed. Therefore, to realize high-precision, non-contact, fast and stable measurement of the thickness of each layer in the multi-layer film structure has become an important technical requirement in optical manufacturing and semiconductor process. The common non-contact film thickness measurement methods include ellipsometry, reflection / transmission interference spectroscopy, and confocal optical imaging. These methods have been relatively mature in practical engineering applications, but there are still many technical bottlenecks when facing multi-layer film structure measurement.

[0003] The ellipsometry uses the change of polarization state of polarized light in the reflection process of the sample to extract parameters related to film thickness and refractive index. The core is to establish a model and inverse the film layer characteristics by analyzing the amplitude ratio (Ψ) and phase difference (Δ) in the reflected light. This technology has very high sensitivity to very thin film layers, and is widely used in nanometer structure research and semiconductor manufacturing. However, the ellipsometry measurement results are highly dependent on model fitting, especially in multi-layer film systems, due to the dramatic increase in the number of parameters, often resulting in the "non-uniqueness" problem that multiple solutions can fit the experimental data. In addition, the ellipsometry method is complex to construct, requiring precise polarization control elements and rotating mechanisms, resulting in high equipment and maintenance costs.

[0004] The reflection / transmission spectroscopy is based on the interference effect between the interfaces of the multi-layer film, and the film thickness is obtained by recording the interference spectrum and combining with the theoretical model fitting. This method is simple in device and convenient in operation, and is often combined with a fiber spectrometer for on-site rapid detection. It is particularly effective for transparent films or systems with large differences in interlayer refractive index. However, when the number of film layers is large and the refractive index is close, the interference signals generated by different interfaces will be coupled, resulting in complex spectral characteristics and blurred interference fringes, thereby increasing the difficulty of data analysis. In addition, this method usually requires relatively accurate prior information (such as the number of layers, materials), otherwise it is easy to introduce calculation bias.

[0005] The confocal optical imaging technology utilizes high-precision optical focusing to detect the reflection signals of different depths of the sample, thereby obtaining the interlayer distance and realizing the film thickness measurement. This method performs outstandingly in spatial resolution and positioning accuracy, and is particularly suitable for the detection of high-reflective interfaces or thick transparent films. However, the measurement speed and accuracy of this method are limited by the scanning mechanism, and the scanning mechanism has extremely high requirements. Meanwhile, the selection of the objective lens is also crucial, and different specifications of objective lenses need to be equipped for different thickness ranges.

[0006] In summary, the current mainstream non-contact film thickness measurement methods still have many limitations in dealing with multi-layer film structures, and therefore, it is urgent to develop a new type of non-contact multi-layer film thickness measurement scheme with the characteristics of simple structure, low cost, low data analysis difficulty, accurate, stable and fast measurement to meet the development needs of new generation of optoelectronic devices and micro-nano manufacturing processes. SUMMARY

[0007] Therefore, it is necessary to provide a multi-layer film thickness high-precision measurement system and method based on low-coherence interference in view of the above problems.

[0008] To solve the above problems, the present disclosure adopts the following technical solutions:

[0009] In a first aspect, the present disclosure provides a multi-layer film thickness high-precision measurement system based on low-coherence interference, comprising a low-coherence broadband light source, a fiber coupling module, a Y-shaped multimode optical fiber, a collimation module, a full-fiber reflective coaxial probe, a spectrometer and a data processing module. The low-coherence broadband light source, the fiber coupling module and one end of the bifurcated end of the Y-shaped multimode optical fiber are sequentially arranged in correspondence. The common end of the Y-shaped multimode optical fiber, the collimation module and the full-fiber reflective coaxial probe are sequentially arranged in correspondence. The other end of the bifurcated end of the Y-shaped multimode optical fiber is arranged in correspondence with the spectrometer. The spectrometer is connected to the data processing module. The full-fiber reflective coaxial probe is used to vertically irradiate a collimated light beam to the surface of a measured multi-layer film structure sample and collect the reflected light of the measured multi-layer film structure sample. The spectrometer is used to obtain the spectral data of the light beam output from the other end of the bifurcated end of the Y-shaped multimode optical fiber. The data processing module is used to perform Fourier transform on the spectral data, separate the optical path difference signals of each interface and calculate the thickness information of the film in the measured multi-layer film structure sample.

[0010] In a preferred embodiment, the light emitted by the low-coherence broadband light source is white light.

[0011] In a preferred embodiment, the low-coherence broadband light source adopts a light-emitting diode

[0012] In a preferred embodiment, the collimation module adopts a self-focusing gradient refractive index lens.

[0013] In a preferred embodiment, the spectral resolution of the spectrometer can reach the level of 0.10 nm.

[0014] In a preferred embodiment, the spectral data is a spectral interference signal, and the data processing module is specifically configured to perform a fast Fourier transform on the spectral interference signal, map the spectral interference signal from the wavelength domain to the optical path difference domain, decouple the reflection peaks generated by different film layer interfaces of the measured multi-layer film structure sample in the optical path difference domain, and extract the optical thickness information corresponding to each interface.

[0015] In a second aspect, the present disclosure provides a multi-layer film thickness high-precision measurement method based on low-coherence interference, which uses the multi-layer film thickness high-precision measurement system based on low-coherence interference as described in the first aspect. The measurement method comprises:

[0016] Placing the measured multi-layer film structure sample at the all-fiber reflective coaxial probe;

[0017] Starting the low-coherence broadband light source, the all-fiber reflective coaxial probe, the spectrometer, and the data processing module, so that the low-coherence broadband light source outputs low-coherence broadband light, the fiber coupling module couples the low-coherence broadband light to one end of the bifurcated end of the Y-type multimode optical fiber, the low-coherence broadband light coupled to the other end of the bifurcated end of the Y-type multimode optical fiber is output to the collimating module through the common end of the Y-type multimode optical fiber, collimated light is obtained after collimating by the collimating module, the collimated light is incident into the all-fiber reflective coaxial probe, irradiates onto the measured multi-layer film structure sample through the all-fiber reflective coaxial probe, collects the reflected light of the measured multi-layer film structure sample, the reflected light enters the common end of the Y-type multimode optical fiber in sequence through the collimating module, and then is output through the other end of the bifurcated end of the Y-type multimode optical fiber, and the spectrometer acquires the spectral data of the reflected light, the data processing module performs Fourier transform on the spectral data, separates the optical path difference signals of each interface, and calculates the thickness information of the thin film in the measured multi-layer film structure sample.

[0018] The multi-layer film thickness high-precision measurement system and method based on low-coherence interference of the present disclosure are based on the low-coherence interference principle, use the fiber coupling module, the Y-type multimode optical fiber, the collimating module, the all-fiber reflective coaxial probe, and the data processing module, so that the system has a simple structure and low cost, can realize fast measurement, realizes the separation of interface signals in the optical path difference domain by using Fourier transform, has low data analysis difficulty, and has high accuracy and stability in thickness measurement. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 FIG. 1 is a structural schematic diagram of the system in one embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] The technical solutions of the present disclosure will be described in detail below with reference to the accompanying drawings and preferred embodiments.

[0021] Referring to Figure 1 The present disclosure provides a kind of low coherence interference-based multilayer film thickness high-precision measurement system, including low coherence broadband light source 1, optical fiber coupling module 2, Y type multimode optical fiber 3, collimating module 4, all-fiber reflective coaxial probe 5, spectrometer 6 and data processing module 7, the low coherence broadband light source 1, optical fiber coupling module 2, the bifurcated end of Y type multimode optical fiber 3 one end is sequentially arranged, the common end of Y type multimode optical fiber 3, collimating module 4, all-fiber reflective coaxial probe 5 sequentially correspond to be arranged, the bifurcated end of Y type multimode optical fiber 3 other end corresponds the arrangement of spectrometer 6, and spectrometer 6 is connected data processing module 7;The all-fiber reflective coaxial probe 5 is used to collimate light beam vertically irradiated to the surface of the measured multilayer film structure sample and collects the reflected light of the measured multilayer film structure sample, the spectrometer 6 is used to obtain the spectrum data of the other end output beam of the bifurcated end of Y type multimode optical fiber 3, and the data processing module 7 is used to Fourier transform the spectrum data, separates the optical path difference signal of each interface, and calculates the thickness information of the film in the measured multilayer film structure sample.

[0022] In the embodiment, the low coherence broadband light source 1 is used for outputting low coherence broadband light. The low coherence broadband light source 1 adopts a broadband white light source, specifically adopts a light emitting diode (LED) as a low coherence interference light source. The low coherence light source has a short coherence length (usually less than the wavelength of light), which effectively avoids multi-path overlapping interference and ensures that the reflected light of different interfaces can be separated in the time domain. By reasonably selecting the center wavelength and the spectral bandwidth, the system has high axial resolution and wide measurement range.

[0023] In the embodiment, the optical fiber coupling module 2 is used for coupling the low coherence broadband light to one end of the bifurcated end of the Y type multimode optical fiber 3.

[0024] In the embodiment, the common end of the Y type multimode optical fiber 3 is used for outputting the low coherence broadband light (entering from one end of the bifurcated end of the Y type multimode optical fiber 3) to the collimating module 4. The collimating module 4 is used for collimating the light input from the common end of the Y type multimode optical fiber 3 and outputting the collimated light to the all-fiber reflective coaxial probe 5. The all-fiber reflective coaxial probe 5 is used for vertically irradiating the collimated light beam to the surface of the measured multilayer film structure sample and collecting the reflected light of the measured multilayer film structure sample. The reflected light enters the common end of the Y type multimode optical fiber 3 after passing through the collimating module 4 and is output from the other end of the bifurcated end of the Y type multimode optical fiber 3. Apparently, the measured multilayer film structure sample is a multilayer film structure to be measured.

[0025] The collimation module 4 adopts a self-focusing gradient refractive index lens (GRIN lens), which effectively collimates the outgoing light of the common end of the Y-shaped multimode optical fiber 3 and vertically enters the surface of the measured multilayer film structure sample. This design ensures that the probe spot diameter matches the numerical aperture (NA), thereby improving the interference fringe contrast and reducing the phase distortion caused by oblique incidence. By optimizing the GRIN lens pitch and the optical fiber parameters, the signal-to-noise ratio and measurement stability of the system can be significantly enhanced.

[0026] The all-fiber reflective coaxial probe 5, the present disclosure adopts a reflective probe with a coaxial design, which transmits the reference light and the measurement light in the same path, avoiding the instability factors caused by the beam splitting structure of the traditional Michelson interferometer. This design has the advantages of compact structure, strong vibration resistance, and small optical path drift, and is especially suitable for online detection requirements in industrial environments.

[0027] The spectrometer 6, the reflected signal of each interface of the measured multilayer film structure sample is collected by the optical fiber and introduced into the spectrometer 6 for detection and recording. The present disclosure selects a high-resolution spectrometer (such as a spectral resolution of 0.10 nm level), which can cover a film thickness measurement range of tens of nanometers to several microns. The spectral data is digitized and collected and input into the signal processing module, ensuring accurate calculation of subsequent algorithms.

[0028] The signal processing module is based on Fourier transform layer demodulation and thickness inversion. Specifically, the spectral data (i.e. spectral interference signal) is subjected to Fast Fourier Transform (FFT), which maps the spectral interference signal from the wavelength domain to the optical path difference domain. The reflection peaks generated by different film layer interfaces are decoupled in the optical path difference domain, thereby extracting the optical thickness information corresponding to each interface. Combined with the refractive index parameters of the material and the adaptive fitting algorithm, the physical thickness of each film layer can be accurately inverted, avoiding the excessive dependence of traditional methods on complex model fitting.

[0029] The present disclosure provides a low-coherence interference-based multilayer film thickness high-precision measurement method, which adopts a low-coherence interference-based multilayer film thickness high-precision measurement system. The measurement method comprises:

[0030] Place the measured multilayer film structure sample at the all-fiber reflective coaxial probe 5;

[0031] The low-coherence broadband light source 1, the all-fiber reflective coaxial probe 5, the spectrometer 6 and the data processing module 7 are started, so that the low-coherence broadband light source 1 outputs low-coherence broadband light, the fiber coupling module 2 couples the low-coherence broadband light to one end of the bifurcated end of the Y-type multimode optical fiber 3, the low-coherence broadband light coupled to one end of the bifurcated end of the Y-type multimode optical fiber 3 is output to the collimation module 4 through the common end of the Y-type multimode optical fiber 3, collimated light is obtained after collimation through the collimation module 4, the collimated light is incident into the all-fiber reflective coaxial probe 5, irradiates onto the measured multilayer film structure sample through the all-fiber reflective coaxial probe 5, collects the reflected light of the measured multilayer film structure sample, the reflected light is sequentially input into the common end of the Y-type multimode optical fiber 3 through the collimation module 4, and then the light is output through the other end of the bifurcated end of the Y-type multimode optical fiber 3, and the spectral data of the light is acquired by the spectrometer 6, the data processing module 7 performs Fourier transform on the spectral data, separates the optical path difference signals of each interface, and calculates the thickness information of the film in the measured multilayer film structure sample.

[0032] The present disclosure is a kind of low-coherence interference-based multilayer film thickness high-precision measurement system and method, based on low-coherence interference principle, the fiber coupling module 2, Y-type multimode optical fiber 3, collimation module 4, all-fiber reflective coaxial probe 5 and data processing module 7 are adopted, so that the system structure is simple, the cost is low, the rapid measurement can be realized, the interface signal separation can be realized in the optical path difference domain by using Fourier transform, the data analysis difficulty is low, and the accuracy and stability of thickness measurement are high.

[0033] Specifically:

[0034] Compared with the ellipsometry method, the present disclosure directly separates the interface signal in the optical path difference domain by the low-coherence interference principle combined with Fourier layered demodulation, reduces the dependence on complex models, and avoids the non-unique problem; the design of the fiber combined with the collimation module 4 and the probe makes the system structure compact, saves the rotating mechanism, and reduces the system complexity and cost.

[0035] Compared with the reflection / transmission spectrum method, the present disclosure uses a low-coherence broadband light source 1 to naturally separate the reflections of different interfaces in the time domain, and then Fourier analysis can extract the thickness information of each layer, which reduces the data analysis difficulty and can better adapt to the thickness detection of multilayer film structure. Therefore, compared with the spectrum method, the present disclosure does not need accurate prior information, and the present disclosure has stronger layering capability and result stability in principle.

[0036] Compared with the confocal optical imaging technology, the present disclosure adopts the all-fiber reflective coaxial probe 5, which can collect interference signals at one time without mechanical scanning, can realize rapid detection, and is suitable for real-time measurement and online application. Moreover, the present disclosure is equipped with different specifications of objective lenses for different thickness ranges. In addition, the coaxial optical path design has good anti-vibration performance and is more suitable for industrial environments.

[0037] Specifically, the present disclosure guarantees the miniaturization of the overall system device; the present disclosure is suitable for various application environments; the method of the present disclosure is simple;

[0038] Specifically, the algorithm and hardware architecture involved in the present disclosure have good scalability, can support the docking with an automated detection platform, and meet the high-throughput and real-time feedback requirements of industrial process control.

[0039] The technical features of the above-described embodiments can be combined arbitrarily, and to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist contradictory, they should be considered as the scope of the present disclosure.

[0040] The above-described embodiments only express several implementation manners of the present disclosure, the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled persons in the art, several modifications and improvements can be made without departing from the concept of the present disclosure, and these all belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure should be subject to the appended claims.

Claims

1. A low coherence interferometry based high precision multilayer film thickness measurement system, characterized in that, The application relates to a low-coherence interference-based multilayer film thickness high-precision measuring system, which comprises a low-coherence broadband light source, a fiber coupling module, a Y-shaped multimode optical fiber, a collimation module, a full-fiber reflective coaxial probe, a spectrometer and a data processing module, wherein one end of the low-coherence broadband light source, the fiber coupling module and the bifurcated end of the Y-shaped multimode optical fiber are sequentially arranged in correspondence, the common end of the Y-shaped multimode optical fiber, the collimation module and the full-fiber reflective coaxial probe are sequentially arranged in correspondence, the other end of the bifurcated end of the Y-shaped multimode optical fiber is arranged in correspondence with the spectrometer, and the spectrometer is connected with the data processing module; the full-fiber reflective coaxial probe is used for vertically irradiating a collimated light beam to the surface of a measured multilayer film structure sample and collecting reflected light of the measured multilayer film structure sample; the spectrometer is used for acquiring spectral data of the light beam output from the other end of the bifurcated end of the Y-shaped multimode optical fiber; and the data processing module is used for performing Fourier transform on the spectral data, separating out optical path difference signals of each interface and calculating thickness information of the film in the measured multilayer film structure sample.

2. The system for high-precision measurement of the thickness of a multilayer film based on low-coherence interference according to claim 1, characterized in that The light emitted by the low-coherence broadband light source is white light.

3. The system for high-precision measurement of the thickness of a multilayer film based on low-coherence interference according to claim 1 or 2, characterized in that The low-coherence broadband light source adopts a light-emitting diode.

4. The system for high-precision measurement of the thickness of a multilayer film based on low-coherence interference according to claim 1, characterized in that The collimation module adopts a self-focusing gradient refractive index lens.

5. The system for high-precision measurement of the thickness of a multilayer film based on low-coherence interference according to claim 1, characterized in that The spectral resolution of the spectrometer can reach 0.10 nm level.

6. The system for high-precision measurement of the thickness of a multilayer film based on low-coherence interference according to claim 1, characterized in that The spectral data is a spectral interference signal, and the data processing module is specifically used for performing fast Fourier transform on the spectral interference signal, mapping the spectral interference signal from a wavelength domain to an optical path difference domain, realizing decoupling of reflection peaks generated by different film layer interfaces of the measured multilayer film structure sample in the optical path difference domain and extracting optical thickness information corresponding to each interface.

7. A method for high-precision measurement of the thickness of a multilayer film based on low-coherence interferometry, characterized in that The application discloses a low-coherence interference-based multilayer film thickness high-precision measuring system and a measuring method thereof. The measured multilayer film structure sample is placed at the full-fiber reflective coaxial probe; The low-coherence broadband light source, the full-fiber reflective coaxial probe, the spectrometer and the data processing module are started, so that the low-coherence broadband light source outputs low-coherence broadband light, the fiber coupling module couples the low-coherence broadband light to one end of the bifurcated end of the Y-shaped multimode optical fiber, the coherent broadband light coupled to the one end of the bifurcated end of the Y-shaped multimode optical fiber is output to the collimation module through the common end of the Y-shaped multimode optical fiber, collimated light is obtained after the collimation module, the collimated light is incident into the full-fiber reflective coaxial probe, irradiated to the measured multilayer film structure sample through the full-fiber reflective coaxial probe, the reflected light of the measured multilayer film structure sample is collected, the reflected light is sequentially input into the common end of the Y-shaped multimode optical fiber through the collimation module, and then the spectral data of the reflected light is acquired by the spectrometer after being output through the other end of the bifurcated end of the Y-shaped multimode optical fiber, the data processing module performs Fourier transform on the spectral data, separates out optical path difference signals of each interface and calculates thickness information of the film in the measured multilayer film structure sample.

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