A film thickness measuring device and method

Abstract

The application discloses a kind of film thickness measuring device and method.The reflective film thickness measuring module in film thickness measuring device is used to obtain the calibration position reflection spectrum information of first reflected light signal reflected by film at calibration position;Photoacoustic film thickness measuring module is used to emit second incident light signal and third incident light signal to calibration position in turn, obtains and analyzes third reflected light signal reflected by film to determine the first thickness information of calibration position;Control module is used to determine the actual refractive index and actual extinction coefficient of film according to calibration position reflection spectrum information, reflectivity theoretical calculation formula of film and first thickness information;Reflective film thickness measuring module is also used to obtain the calibration position reflection spectrum information of first reflected light signal reflected by film at to-be-measured position;Control module is also used to determine the thickness information of to-be-measured position according to actual refractive index, actual extinction coefficient and calibration position reflection spectrum information.The accuracy of film thickness measurement can be improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a thin film thickness measuring device and method. Background Technology

[0002] Precise control of thin film thickness is crucial in the manufacturing processes of wafers, MEMS devices, and precision optical components. Optical thickness measurement devices (such as reflective film thickness gauges) are widely used in the industry, but their measurement models are based on known and stable optical constants. In actual production, even slight variations in material composition, film formation conditions, and post-processing can cause drift in the optical constants of the thin film, leading to significant errors in traditional optical measurement methods and severely impacting product yield. Currently, mainstream non-destructive measurement technologies suffer from the following pain points:

[0003] Optical reflection method: Although fast, low-cost, and technologically mature, its principle is to inversely determine the thickness by measuring changes in light intensity. A fatal flaw is that the thickness measurement results are heavily dependent on the optical constants of the thin film (refractive index n and extinction coefficient k). When the optical constants of the thin film change due to process variations, different material batches, or the presence of surface / interface effects, the measurement results of the reflection method will produce huge errors, or even become invalid.

[0004] Photoacoustic method: Its principle is to use pulsed laser to irradiate the surface of a thin film to generate a thermoelastic effect, which in turn excites ultrasonic waves. The thickness is calculated by detecting the ultrasonic signals. Its biggest advantage is that the velocity of sound waves mainly depends on the density and elastic modulus of the material and is not sensitive to changes in optical constants. Therefore, the photoacoustic method can provide a near-absolute geometric thickness reference that is independent of optical properties. However, its disadvantages may include relatively low lateral resolution or high equipment cost.

[0005] Therefore, there is an urgent need in this field for a measurement scheme that can maintain the advantages of optical reflection methods in terms of speed and low cost, while overcoming the influence of changes in optical constants. Summary of the Invention

[0006] This invention provides a thin film thickness measurement device and method to solve the technical problem that the measurement results of the reflection method in the prior art are greatly affected by the optical constant of the thin film, and to achieve fast, low-cost and high-precision thin film thickness measurement.

[0007] In a first aspect, embodiments of the present invention provide a thin film thickness measuring device, wherein the thin film disposed on the sample stage includes a calibration position and multiple positions to be measured;

[0008] The thin film thickness measuring device includes a reflective film thickness measuring module, a photoacoustic film thickness measuring module, and a control module;

[0009] The reflective film thickness measurement module is used to emit a first incident light signal to the calibration position and obtain the calibration position reflectance spectrum information of the first reflected light signal reflected by the film.

[0010] The photoacoustic film thickness measurement module is used to sequentially emit a second incident light signal and a third incident light signal to the calibration position, and acquire and analyze the third reflected light signal reflected by the film to determine the first thickness information of the calibration position; wherein, after the film absorbs the second incident light signal, it will undergo thermoelastic deformation and generate ultrasonic waves propagating along the thickness direction of the film, and when the ultrasonic waves propagate to the surface of the film, the surface of the film will vibrate; the phase of the third reflected light signal reflected by the film when the ultrasonic waves propagate to the surface of the film is different from the phase of the third reflected light signal reflected by the film when the ultrasonic waves do not propagate to the surface of the film;

[0011] The control module is communicatively connected to the reflective film thickness measurement module and the photoacoustic film thickness measurement module, respectively, and is used to acquire the reflective spectrum information of the calibration position and the first thickness information, and determine the actual refractive index and actual extinction coefficient of the film based on the reflective spectrum information of the calibration position, the theoretical calculation formula of the reflectivity of the film and the first thickness information;

[0012] The reflective film thickness measurement module is also used to emit the first incident light signal to the position to be measured, and to obtain the reflectance spectrum information of the first reflected light signal reflected by the thin film at the position to be measured.

[0013] The control module is further configured to determine the second thickness information of the position to be measured based on the actual refractive index, the actual extinction coefficient, and the reflection spectrum information of the position to be measured.

[0014] Optionally, the reflective film thickness measurement module includes a light source and a spectrometer;

[0015] The light source is used to emit the first incident light signal to the thin film, wherein the first incident light signal includes light signals with continuous wavelengths;

[0016] The spectrometer is used to acquire the calibrated position reflection spectrum information of the first reflected light signal reflected by the thin film.

[0017] Optionally, the photoacoustic film thickness measurement module includes a pulsed laser, a probe laser, and a thickness determination unit;

[0018] The pulsed laser is used to emit the second incident light signal to the calibrated position, wherein the second incident light signal includes a pulsed laser.

[0019] The detection laser is used to emit the third incident light signal to the calibrated position and acquire the third reflected light signal reflected by the thin film, wherein the third incident light signal includes continuous laser light;

[0020] The thickness determination unit is communicatively connected to the detection laser and is used to acquire the third reflected light signal and demodulate the third reflected light signal to obtain the time difference information of the ultrasonic wave making one round trip within the thin film, and then determine the first thickness information based on the time difference information.

[0021] Optionally, the thickness determining unit is used to determine the first thickness information based on the time difference information and the following correspondence:

[0022] ;

[0023] in, This indicates the first thickness information. This indicates the speed of sound of the ultrasonic wave in the thin film. This indicates the time difference information.

[0024] Optionally, the control module is used to determine the reflectance change information at the calibration position based on the reflectance spectrum information at the calibration position, and substitute the first thickness information as a fixed constraint into the theoretical calculation formula of the reflectance of the thin film to obtain the actual refractive index and the actual extinction coefficient that minimize the difference between the reflectance change information at the calibration position and the theoretical reflectance change information of the thin film.

[0025] The control module is further configured to determine the reflectance change information of the test location based on the reflectance spectrum information of the test location, and to determine the second thickness information of the test location based on the actual refractive index, the actual extinction coefficient and the reflectance change information of the test location.

[0026] Optionally, the thin film thickness measuring device further includes a first focusing optical component and a second focusing optical component;

[0027] The first focusing optical component is located in the optical path between the reflective film thickness measurement module and the thin film, and is used to focus the first incident light signal emitted by the reflective film thickness measurement module;

[0028] The second focusing optical component is located in the optical path between the photoacoustic film thickness measurement module and the thin film, and is used to focus the second incident light signal emitted by the photoacoustic film thickness measurement module.

[0029] Optionally, the first focusing optical component and the second focusing optical component share the same focusing optical component.

[0030] In a second aspect, embodiments of the present invention provide a thin film thickness measurement method, applied to the thin film thickness measurement device described in the first aspect, the thin film thickness measurement method comprising:

[0031] Obtain the reflection spectrum information of the calibration location and the first thickness information;

[0032] The actual refractive index and actual extinction coefficient of the thin film are determined based on the reflection spectrum information at the calibration location, the theoretical calculation formula for the reflectance of the thin film, and the first thickness information.

[0033] Obtain the reflectance spectrum information of the location to be measured;

[0034] The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance spectrum information of the location to be measured.

[0035] Optionally, the actual refractive index and actual extinction coefficient of the thin film are determined based on the calibrated position reflectance spectrum information, the theoretical calculation formula for the reflectance of the thin film, and the first thickness information, including:

[0036] The reflectance variation information at the calibration location is determined based on the reflectance spectrum information at the calibration location.

[0037] The first thickness information is substituted into the theoretical calculation formula of the reflectivity of the thin film as a fixed constraint to obtain the actual refractive index and the actual extinction coefficient that minimize the difference between the reflectivity change information at the calibration position and the theoretical reflectivity change information of the thin film.

[0038] The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance spectral information of the location to be measured, including:

[0039] The reflectance variation information of the test location is determined based on the reflectance spectrum information of the test location;

[0040] The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance change information of the location to be measured.

[0041] Optionally, before obtaining the first thickness information, the film thickness measurement method further includes:

[0042] Obtain the true thickness information of standard thin film samples;

[0043] The photoacoustic thickness information of the standard thin film sample is obtained through the photoacoustic film thickness measurement module.

[0044] The photoacoustic film thickness measurement module is calibrated based on the actual thickness information and the photoacoustic thickness information.

[0045] The technical solution of this invention first determines the actual refractive index and actual extinction coefficient of the thin film based on the reflection spectrum information of the calibration position of the thin film obtained by the reflection film thickness measurement module and the first thickness information of the thin film at the calibration position obtained by the photoacoustic film thickness measurement module. Then, the thickness of the thin film can be rapidly measured using only the determined actual refractive index and actual extinction coefficient of the thin film and the reflection spectrum information of the test position of the thin film obtained by the reflection film thickness measurement module. This enables non-destructive, rapid and accurate measurement of thin films with unknown or changing optical constants.

[0046] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of a thin film thickness measuring device provided in an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of another thin film thickness measuring device provided in an embodiment of the present invention;

[0050] Figure 3 This is a flowchart of a thin film thickness measurement method provided in an embodiment of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0052] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus. The terms "upper," "lower," "left," "right," etc., indicate orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings and are used only to describe the relative positional relationships between components or constituent parts, and do not specifically limit the specific installation orientation of each component or constituent part.

[0053] Figure 1 This is a schematic diagram of a thin film thickness measuring device provided in an embodiment of the present invention, with reference to... Figure 1 It should be noted that, in this embodiment of the invention, the thin film 200 set on the sample stage 100 includes a calibration position and multiple test positions; the thin film thickness measuring device in this embodiment of the invention includes a reflective film thickness measuring module 10, a photoacoustic film thickness measuring module 20 and a control module 30.

[0054] Specifically, the reflective film thickness measurement module 10 is used to emit a first incident light signal to the calibration position and acquire the calibration position reflection spectrum information of the first reflected light signal reflected by the thin film 200.

[0055] As one possible implementation method, refer to Figure 1 The reflective film thickness measurement module 10 in this embodiment of the invention includes a light source 11 and a spectrometer 12; the light source 11 is used to emit a first incident light signal to the thin film 200, wherein the first incident light signal includes a light signal with continuous wavelength; the spectrometer 12 is used to acquire the calibrated position reflection spectrum information of the first reflected light signal reflected by the thin film 200.

[0056] For example, the light source 11 in this embodiment of the invention can be a broadband light source, such as a halogen lamp. A broadband light source can provide a first incident light signal with continuous wavelengths (typically covering the ultraviolet-visible-near-infrared band, for example, 300nm-1100nm) to ensure that the spectrum of the first reflected light signal after reflection by the thin film 200 contains sufficient interference information. The broadband spectral characteristics of the halogen lamp are the basis for realizing "white light interference" or "spectral interference." Different wavelengths of light have different interference conditions in the thin film 200, thereby forming a periodic peak-valley structure in the reflection spectrum.

[0057] The spectrometer 12 can analyze the spectral composition of the first reflected light signal reflected by the thin film 200. Specifically, it decomposes the received first reflected light signal by wavelength and outputs a curve showing the intensity of the first reflected light signal as a function of wavelength (i.e., the reflected spectral information at the calibration position mentioned above). It should be noted that the reflective film thickness measurement module 10 in this embodiment can provide fast, high-resolution information on the change in reflected light intensity. This information is closely related to the thickness of the thin film 200 and its optical constants (refractive index and extinction coefficient), and forms the basis for rapid scanning.

[0058] The photoacoustic film thickness measurement module 20 is used to sequentially emit a second incident light signal and a third incident light signal to the calibration position, and to acquire and analyze the third reflected light signal reflected by the film 200 to determine the first thickness information of the calibration position. The film 200 will undergo thermoelastic deformation after absorbing the second incident light signal and generate ultrasonic waves that propagate along the thickness direction of the film 200. When the ultrasonic waves propagate to the surface of the film 200, the surface of the film 200 will vibrate. The phase of the third reflected light signal reflected by the film 200 when the ultrasonic waves propagate to the surface of the film 200 is different from the phase of the third reflected light signal reflected by the film 200 when the ultrasonic waves do not propagate to the surface of the film 200.

[0059] As one possible implementation method, refer to Figure 1 In this embodiment of the invention, the photoacoustic film thickness measurement module 20 includes a pulsed laser 21, a probe laser 22, and a thickness determination unit 23. The pulsed laser 21 is used to emit a second incident light signal to a calibration position, wherein the second incident light signal includes a pulsed laser. The probe laser 22 is used to emit a third incident light signal to the calibration position and acquire a third reflected light signal reflected by the thin film 200, wherein the third incident light signal includes a continuous laser. The thickness determination unit 23 is communicatively connected to the probe laser 22 and is used to acquire the third light signal received by the probe laser 22 and demodulate the third light signal to obtain the time difference information of the ultrasonic wave traveling back and forth once within the thin film 200, and then determine the first thickness information based on the time difference information.

[0060] As one feasible implementation, the detection laser 22 in this embodiment of the invention can be an interferometer. It should be noted that the detection laser 22 in this embodiment of the invention can be not only an interferometer, but also a piezoelectric sensor; there is no limitation on this.

[0061] For example, in this embodiment of the invention, the pulsed laser 21 can emit pulsed laser (e.g., short pulsed laser) to the calibration position of the thin film 200. The laser energy of the pulsed laser incident on the calibration position of the thin film 200 is absorbed by the surface of the thin film 200, and instantaneously generates thermal expansion, exciting ultrasonic waves. The probe laser 22 can emit a continuous laser beam to the calibration position of the thin film 200. It is understood that the ultrasonic waves propagating along the thickness direction of the thin film 200 will cause tiny vibrations each time they propagate to the surface of the calibration position of the thin film 200. These tiny vibrations will change the phase of the continuous laser incident on the calibration position of the thin film 200. The changed continuous laser will be reflected by the thin film 200 and received by the probe laser 22. The thickness determination unit 23 can obtain the time difference information of the ultrasonic waves traveling one round trip within the thin film 200 by analyzing the phase change of the third reflected light signal received by the probe laser 22. Then, it can determine the first thickness information at the calibration position of the thin film 200 based on the time difference information of the ultrasonic waves traveling one round trip within the thin film 200. It should be noted that the photoacoustic film thickness measurement module 20 measures the thickness of the film 200 based on the thermoelastic effect. Its measurement results are not sensitive to the optical constants of the film 200 and can provide a near-absolute thickness reference.

[0062] Specifically, the thickness determination unit 23 in this embodiment of the invention is used to determine the first thickness information based on the time difference information and the following correspondence:

[0063] .

[0064] in, Indicates the first thickness information. This indicates the speed of sound of ultrasound in the thin film 200. This indicates the time difference information.

[0065] The control module 30 is communicatively connected to the reflective film thickness measurement module 10 and the photoacoustic film thickness measurement module 20, respectively, and is used to acquire the reflection spectrum information and the first thickness information at the calibration position. Based on the reflection spectrum information at the calibration position, the theoretical calculation formula of the reflectivity of the thin film 200, and the first thickness information, the actual refractive index and the actual extinction coefficient of the thin film 200 are determined.

[0066] Specifically, the control module 30 is used to determine the reflectance change information at the calibration position based on the reflectance spectrum information at the calibration position, and substitute the first thickness information as a fixed constraint into the theoretical reflectance calculation formula of the thin film 200 to obtain the actual refractive index and actual extinction coefficient that minimize the difference between the reflectance change information at the calibration position and the theoretical reflectance change information of the thin film.

[0067] The core of the control module 30 is a computer or embedded system that can run data fusion algorithm software, coordinate the work of the reflective film thickness measurement module 10 and the photoacoustic film thickness measurement module 20, and perform joint calculations. Specifically, the control module 30 can control the selection of measurement points by controlling the movement of the sample stage 100, and will also synchronously trigger the operation of the reflective film thickness measurement module 10 and the photoacoustic film thickness measurement module 20 to ensure that they measure the same point (calibration position).

[0068] The thickness and reflectivity of thin film 200 can be inverted by analyzing the interference spectrum generated by a broadband light source on the thin film 200 and sample stage 100. The theoretical calculation formula (optical reflection model) is as follows:

[0069] , , where d is the thickness of the film 200 (e.g., the film 200 at the calibration position).

[0070] Fresnel reflectance at the interface between ambient medium (air) and thin film 200 The calculation formula is as follows:

[0071] .

[0072] Fresnel reflectance at the interface between thin film 200 and sample stage 100 The calculation formula is as follows:

[0073] .

[0074] It should be noted that, Let be the complex refractive index of air. Let be the complex refractive index of the thin film 200. Let be the complex refractive index of sample stage 100. The following relationship must be satisfied: , where n is the refractive index of air, thin film 200 or sample stage 100, and k is the extinction coefficient of air, thin film 200 or sample stage 100.

[0075] If only known Then d needs to be solved simultaneously. , This is a highly ill-conditioned inverse problem with multiple solutions, leading to unreliable measurement results. However, the first thickness information at the calibration position of the thin film 200 obtained by the photoacoustic film thickness measurement module 20 is a reliable thickness constraint unaffected by the optical model. This information can be substituted into the reflectivity theoretical calculation formula to obtain the actual refractive index and actual extinction coefficient that meet the preset conditions. It should be noted that the preset condition is to minimize the difference between the theoretically calculated reflection spectrum Rmodel(λ) (i.e., the theoretical change information of the thin film reflectivity corresponding to the theoretical calculation formula) and the measured spectrum Rmeasured(λ) (i.e., the change information of the reflectivity at the calibration position determined based on the reflection spectrum information at the calibration position). This can be transformed into a nonlinear least squares optimization problem, with the specific formula as follows:

[0076] .

[0077] Through this process, the theoretically optimal optical constants can be obtained, namely the actual refractive index and actual extinction coefficient that can meet the preset conditions. Then, the thickness information of the thin film 200 at the measurement position can be quickly measured using the determined actual refractive index and actual extinction coefficient and the reflective film thickness measurement module 10.

[0078] The reflective film thickness measurement module 10 is also used to emit a first incident light signal to the position to be measured and to acquire the reflective spectral information of the position to be measured of the first reflected light signal reflected by the thin film 200.

[0079] The control module 30 is also used to determine the second thickness information of the position to be measured based on the actual refractive index, the actual extinction coefficient and the reflection spectrum information of the position to be measured.

[0080] Specifically, the control module 30 is also used to determine the reflectance change information of the position to be measured based on the reflectance spectrum information of the position to be measured, and to determine the second thickness information of the position to be measured based on the actual refractive index, the actual extinction coefficient and the reflectance change information of the position to be measured.

[0081] Once the actual refractive index and actual extinction coefficient of the thin film 200 are known, it is only necessary to obtain the reflectivity change information at the test location of the thin film 200 to determine the thickness information at the test location. This ensures accuracy while leveraging the speed advantage of the reflection method.

[0082] The technical solution of this invention first determines the actual refractive index and actual extinction coefficient of the thin film 200 based on the reflection spectrum information of the calibration position of the thin film 200 obtained by the reflection film thickness measurement module 10 and the first thickness information of the thin film 200 at the calibration position obtained by the photoacoustic film thickness measurement module 20. Then, by using only the determined actual refractive index and actual extinction coefficient of the thin film 200 and the reflection spectrum information of the thin film 200 at the test position obtained by the reflection film thickness measurement module 10, the thickness of the thin film 200 can be rapidly measured, realizing non-destructive, rapid and accurate measurement of the thin film 200 with unknown or changing optical constants.

[0083] Figure 2 This is a schematic diagram of another thin film thickness measuring device provided in an embodiment of the present invention, with reference to... Figure 2 The thin film thickness measuring device in this embodiment of the invention further includes a first focusing optical component 40 and a second focusing optical component 50; the first focusing optical component 40 is located in the optical path between the reflective film thickness measuring module 10 and the thin film 200, and is used to focus the first incident light signal emitted by the reflective film thickness measuring module 10; the second focusing optical component 50 is located in the optical path between the photoacoustic film thickness measuring module 20 and the thin film 200, and is used to focus the second incident light signal emitted by the photoacoustic film thickness measuring module 20.

[0084] For example, the first focusing optical component 40 and the second focusing optical component 50 in the embodiments of the present invention can be optical probes or microscope objectives, which can focus the passing light signal into a micron-sized tiny light spot and accurately project it onto the target measurement area (calibration position or position to be measured) on the surface of the thin film 200, while ensuring concentrated light energy, which is suitable for the needs of small sample or local thickness detection.

[0085] As a feasible implementation, the first focusing optical component 40 and the second focusing optical component 50 in this embodiment of the invention share the same focusing optical component.

[0086] The embodiments of the present invention, by setting the first focusing optical component 40 and the second focusing optical component 50 to share the same focusing optical component, are beneficial to reducing measurement costs.

[0087] Optionally, the thin film thickness measuring device in this embodiment of the invention further includes a collimating lens, a beam splitter, and a dichroic mirror. Specifically, the light emitted from the broadband light source is first collimated by the lens, then refracted by the beam splitter, and then passes through the dichroic mirror. Finally, it is focused by the first focusing optical component 40 (e.g., a microscope objective) onto the calibrated position or the position to be measured of the thin film 200. The reflected light carrying the interference information of the thin film 200 also returns along the original path, and is received by the spectrometer 12 after passing through the beam splitter.

[0088] The specific functions of each component in the above optical path are as follows:

[0089] Collimating lens: The light emitted by a broadband light source is divergent. A collimating lens converts the divergent light into parallel light (collimated light) through optical refraction, avoiding the dispersion of light energy and laying the foundation for subsequent precise refraction and focusing.

[0090] The spectroscope's core function is "optical path deflection and subsequent reflected light guidance." It deflects the collimated parallel light at a specific angle (such as 90°) to the direction of the dichroic mirror, and when the sample reflected light returns, it allows the reflected light to pass through or reflect back to the spectrometer 12, thus achieving optical path separation and multiplexing of incident and reflected light.

[0091] Dichroic mirrors are essentially wavelength-selective filtering elements that allow only specific wavelengths of light from broadband light sources (such as 300nm–1100nm required for measurement) to pass through, while filtering out stray light (such as thermal radiation in the infrared band), ensuring the wavelength purity of the incident light and improving the signal-to-noise ratio of subsequent signals.

[0092] This invention also provides a method for measuring film thickness, which is applied to the film thickness measuring device provided in the above embodiments of this invention. Figure 3 A flowchart of a thin film thickness measurement method provided in an embodiment of the present invention is shown below. Figure 3 The method for measuring the thickness of the thin film 200 in this embodiment of the invention includes:

[0093] S110. Obtain the reflection spectrum information and first thickness information of the calibration position.

[0094] For example, refer to Figure 1 The control module 30 in the thin film thickness measuring device can obtain the reflection spectrum information of the calibration position at the calibration position of the thin film 200 through the reflection film thickness measuring module 10, and obtain the first thickness information at the calibration position of the thin film 200 through the photoacoustic film thickness measuring module 20.

[0095] S120. Determine the actual refractive index and actual extinction coefficient of the thin film based on the reflection spectrum information of the calibration position, the theoretical calculation formula of the reflectivity of the thin film, and the first thickness information.

[0096] In one feasible implementation, the actual refractive index and actual extinction coefficient of the thin film are determined based on the reflection spectrum information at the calibration location, the theoretical calculation formula for the reflectivity of the thin film, and the first thickness information. This includes: determining the reflectivity change information at the calibration location based on the reflection spectrum information at the calibration location; and substituting the first thickness information as a fixed constraint into the theoretical calculation formula for the reflectivity of the thin film to obtain the actual refractive index and actual extinction coefficient that minimize the difference between the reflectivity change information at the calibration location and the theoretical reflectivity change information of the thin film.

[0097] S130, Obtain the reflectance spectrum information of the location to be measured.

[0098] For example, refer to Figure 1 The control module 30 in the thin film thickness measuring device can obtain the first reflected light intensity change information at the measurement position of the thin film 200 through the reflective film thickness measuring module 10.

[0099] S140. Determine the second thickness information of the position to be measured based on the actual refractive index, the actual extinction coefficient, and the reflection spectrum information of the position to be measured.

[0100] In one feasible implementation, determining the second thickness information of the test location based on the actual refractive index, the actual extinction coefficient, and the reflectance spectrum information of the test location includes: determining the reflectance change information of the test location based on the reflectance spectrum information of the test location; and determining the second thickness information of the test location based on the actual refractive index, the actual extinction coefficient, and the reflectance change information of the test location.

[0101] Before obtaining the first thickness information, the thin film thickness measurement method also includes: obtaining the true thickness information of a standard thin film sample; obtaining the photoacoustic thickness information of the standard thin film sample through a photoacoustic film thickness measurement module; and calibrating the photoacoustic film thickness measurement module based on the true thickness information and the photoacoustic thickness information.

[0102] For example, before obtaining the first thickness information, a batch of standard samples with known thicknesses (or those precisely measured using destructive methods) can be selected. These samples can be the same material as the film 200 to be tested. The thickness of these standard samples is first measured using the photoacoustic film thickness measurement module 20. Then, the photoacoustic film thickness measurement module 20 is calibrated based on the measured thickness and the known thickness. For example, the calibration of the photoacoustic film thickness measurement module 20 is achieved by compensating for the sound velocity of ultrasound in the film 200, to ensure the accuracy of the photoacoustic module itself.

[0103] This invention achieves a perfect combination of the high speed of the reflection method and the anti-optical interference capability of the photoacoustic method through hardware common-point integration and software data fusion. It effectively solves the industry pain point in semiconductor and high-end manufacturing where changes in the optical constant of thin film 200 due to process fluctuations lead to a decrease in the accuracy of traditional optical measurements. It provides a solution for process control and yield improvement. The specific effects can be summarized as follows:

[0104] 1. High precision and high reliability: It fundamentally solves the measurement error caused by the uncertainty of optical constants in the reflection method, and the measurement accuracy is close to that of the photoacoustic method, with a significant improvement in reliability.

[0105] 2. Balance between cost and efficiency: Compared to expensive ellipsometers, this solution achieves measurement results comparable to ellipsometers by adding only one photoacoustic film thickness measurement module. The measurement efficiency is far higher than using photoacoustic methods alone for full-film scanning.

[0106] 3. High versatility: It is particularly suitable for thin film measurement scenarios where optical constants are unstable or unknown, such as new material development and early-stage process monitoring.

[0107] 4. High degree of automation: The entire calibration and measurement process can be completed automatically by software, making it easy to integrate into automated production lines.

[0108] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A thin film thickness measuring device, characterized in that, The thin film set on the sample stage includes a calibration position and multiple test positions; The thin film thickness measuring device includes a reflective film thickness measuring module, a photoacoustic film thickness measuring module, and a control module; The reflective film thickness measurement module is used to emit a first incident light signal to the calibration position and obtain the calibration position reflectance spectrum information of the first reflected light signal reflected by the film. The photoacoustic film thickness measurement module is used to sequentially emit a second incident light signal and a third incident light signal to the calibration position, and acquire and analyze the third reflected light signal reflected by the film to determine the first thickness information of the calibration position; wherein, after the film absorbs the second incident light signal, it will undergo thermoelastic deformation and generate ultrasonic waves propagating along the thickness direction of the film, and when the ultrasonic waves propagate to the surface of the film, the surface of the film will vibrate; the phase of the third reflected light signal reflected by the film when the ultrasonic waves propagate to the surface of the film is different from the phase of the third reflected light signal reflected by the film when the ultrasonic waves do not propagate to the surface of the film; The control module is communicatively connected to the reflective film thickness measurement module and the photoacoustic film thickness measurement module, respectively, and is used to acquire the reflective spectrum information of the calibration position and the first thickness information, and determine the actual refractive index and actual extinction coefficient of the film based on the reflective spectrum information of the calibration position, the theoretical calculation formula of the reflectivity of the film and the first thickness information; The reflective film thickness measurement module is also used to emit the first incident light signal to the position to be measured, and to obtain the reflectance spectrum information of the first reflected light signal reflected by the thin film at the position to be measured. The control module is further configured to determine the second thickness information of the position to be measured based on the actual refractive index, the actual extinction coefficient, and the reflection spectrum information of the position to be measured.

2. The thin film thickness measuring device according to claim 1, characterized in that, The reflective film thickness measurement module includes a light source and a spectrometer; The light source is used to emit the first incident light signal to the thin film, wherein the first incident light signal includes light signals with continuous wavelengths; The spectrometer is used to acquire the calibrated position reflection spectrum information of the first reflected light signal reflected by the thin film.

3. The thin film thickness measuring device according to claim 1, characterized in that, The photoacoustic film thickness measurement module includes a pulsed laser, a probe laser, and a thickness determination unit; The pulsed laser is used to emit the second incident light signal to the calibrated position, wherein the second incident light signal includes a pulsed laser. The detection laser is used to emit the third incident light signal to the calibrated position and acquire the third reflected light signal reflected by the thin film, wherein the third incident light signal includes continuous laser light; The thickness determination unit is communicatively connected to the detection laser and is used to acquire the third reflected light signal and demodulate the third reflected light signal to obtain the time difference information of the ultrasonic wave making one round trip within the thin film, and then determine the first thickness information based on the time difference information.

4. The thin film thickness measuring device according to claim 3, characterized in that, The thickness determination unit is used to determine the first thickness information based on the time difference information and the following correspondence: ； in, This indicates the first thickness information. This indicates the speed of sound of the ultrasonic wave in the thin film. This indicates the time difference information.

5. The thin film thickness measuring device according to claim 1, characterized in that, The control module is used to determine the reflectance change information at the calibration position based on the reflectance spectrum information at the calibration position, and substitute the first thickness information as a fixed constraint into the theoretical calculation formula of the reflectance of the thin film to obtain the actual refractive index and the actual extinction coefficient that minimize the difference between the reflectance change information at the calibration position and the theoretical reflectance change information of the thin film. The control module is further configured to determine the reflectance change information of the test location based on the reflectance spectrum information of the test location, and to determine the second thickness information of the test location based on the actual refractive index, the actual extinction coefficient and the reflectance change information of the test location.

6. The thin film thickness measuring device according to claim 1, characterized in that, The thin film thickness measuring device further includes a first focusing optical component and a second focusing optical component; The first focusing optical component is located in the optical path between the reflective film thickness measurement module and the thin film, and is used to focus the first incident light signal emitted by the reflective film thickness measurement module; The second focusing optical component is located in the optical path between the photoacoustic film thickness measurement module and the thin film, and is used to focus the second incident light signal emitted by the photoacoustic film thickness measurement module.

7. The thin film thickness measuring device according to claim 6, characterized in that, The first focusing optical component and the second focusing optical component share the same focusing optical component.

8. A method for measuring film thickness, applied to the film thickness measuring device according to any one of claims 1-7, characterized in that, The thin film thickness measurement method includes: Obtain the reflection spectrum information of the calibration location and the first thickness information; The actual refractive index and actual extinction coefficient of the thin film are determined based on the reflection spectrum information at the calibration location, the theoretical calculation formula for the reflectance of the thin film, and the first thickness information. Obtain the reflectance spectrum information of the location to be measured; The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance spectrum information of the location to be measured.

9. The thin film thickness measurement method according to claim 8, characterized in that, The actual refractive index and actual extinction coefficient of the thin film are determined based on the spectral information of the calibration location, the theoretical formula for calculating the reflectance of the thin film, and the first thickness information, including: The reflectance variation information at the calibration location is determined based on the reflectance spectrum information at the calibration location. The first thickness information is substituted into the theoretical calculation formula of the reflectivity of the thin film as a fixed constraint to obtain the actual refractive index and the actual extinction coefficient that minimize the difference between the reflectivity change information at the calibration position and the theoretical reflectivity change information of the thin film. The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance spectral information of the location to be measured, including: The reflectance variation information of the test location is determined based on the reflectance spectrum information of the test location; The second thickness information of the location to be measured is determined based on the actual refractive index, the actual extinction coefficient, and the reflectance change information of the location to be measured.

10. The thin film thickness measurement method according to claim 8, characterized in that, Before acquiring the first thickness information, the film thickness measurement method further includes: Obtain the true thickness information of standard thin film samples; The photoacoustic thickness information of the standard thin film sample is obtained through the photoacoustic film thickness measurement module. The photoacoustic film thickness measurement module is calibrated based on the actual thickness information and the photoacoustic thickness information.

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