A film thickness measurement method based on dispersion confocal sensing principle

Abstract

A film thickness measurement method based on dispersion confocal sensing principle belongs to the technical field of optical precision measurement. In order to solve the problem of accurate measurement of film thickness, the spectrometer detects the peak position of each frame of reflected spectrum in the dispersion envelope range with preset wavelength and scale parameters, obtains a peak position time sequence for high-pass filtering processing, and obtains the peak position time sequence after high-pass filtering processing; the proportion of the sample number of the peak position time sequence after high-pass filtering which exceeds the predetermined threshold in the total sample number in the time window is obtained in the sliding time window, and the time-varying duty ratio is obtained; a closed mapping of the time-varying duty ratio and the film sample thickness is established; the closed mapping is processed based on the time-varying duty ratio, and the film absolute thickness time sequence is obtained by inversion as the final film thickness measurement result based on the dispersion confocal sensing principle. The present application can be implemented in the data processing link of the existing dispersion confocal measurement system.

Description

Technical Field

[0001] This invention belongs to the field of optical precision measurement technology, specifically relating to a thin film thickness measurement method based on the principle of dispersive confocal sensing. Background Technology

[0002] Dispersive confocal sensing is a displacement and thickness measurement technique that uses a dispersive objective lens to focus different wavelengths to different positions on the optical axis and a confocal stop to select the depth. It has been widely used in industrial precision metrology since the 1990s. Extending dispersive confocal sensing to thin film thickness measurement involves a common-path single-fiber architecture combined with peak position geometric inversion: a commercial dispersive confocal probe is projected onto the surface of a liquid film or thin film, and the distance between the wall reflection peak and the liquid surface reflection peak on the pixel axis is used for measurement. The film thickness is obtained by inversion using known dispersion calibration relationships. This approach is effective when the film thickness is greater than the optical path length corresponding to the width of the dispersive confocal envelope. However, when the film thickness is reduced to near or less than this optical path length, the reflection peaks at the upper and lower interfaces coherently superimpose within the same dispersive envelope, making it impossible to distinguish them as two independent geometric peaks by peak position detection. The original "peak distance measurement" method is no longer applicable. The two-arm interferometric architecture requires an external reference arm to match the dispersion, making it sensitive to vibrations and difficult to deploy in vibrating environments such as wind tunnels. Static fitting of the common-path reflection spectrum is suitable for steady-state measurements, but it is difficult to provide instantaneous absolute thickness during dynamic thinning. Summary of the Invention

[0003] The problem this invention aims to solve is how to accurately measure the absolute thickness of a thin film by directly obtaining the time series of the film's absolute thickness from the dispersive confocal reflection spectrum, without relying on external thickness references, film leading edge position information, phase unwinding, or time asymptotic extrapolation, when the film thickness is in the transition range corresponding to the dispersive confocal envelope width (typically on the order of micrometers to tens of micrometers) and the film is in a dynamic thinning process. This invention proposes a thin film thickness measurement method based on the principle of dispersive confocal sensing.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for measuring thin film thickness based on the principle of dispersive confocal sensing includes the following steps:

[0006] S1. Dispersive light is projected onto the thin film sample using a dispersive confocal sensor, and the reflection spectra formed by the reflections from the upper and lower interfaces of the thin film sample and their coherent superposition within the same dispersive envelope are continuously collected to obtain the reflection spectrum time series I(p,t), where p is the pixel coordinate of the spectrometer and t is the sampling time.

[0007] S2. The spectrometer performs peak position detection on each frame of reflectance spectrum obtained in step S1 within the dispersion envelope range with preset wavelength and scale parameters to obtain the peak position time series.

[0008] S3. For the peak position time series p obtained in step S2 max (t) is high-pass filtered to remove the low-frequency baseline component caused by the slow change in film thickness, resulting in the detrended peak offset Δp(t) = H HP {p max (t)}, the detrended peak shift characterizes the rapid sawtooth fluctuations generated by the co-modulation of the interference phase and dispersive envelope at the upper and lower interfaces of the thin film, where H HP It is a high-pass filter;

[0009] S4. Within a sliding time window containing N valid sampling points, the statistics satisfy |Δp(t)|>βσ. e Number of sampling points N e and in accordance with DC obs (t)=N e / N yields the time-varying duty cycle DC obs (t), where β is the dimensionless visible peak threshold, σ e The dispersion envelope scale is expressed in pixels of the spectrometer;

[0010] S5. Establish a closed-form mapping between the time-varying duty cycle obtained in step S4 and the thickness of the thin film sample;

[0011] S6. Based on the time-varying duty cycle obtained in step S4, the closed-form mapping obtained in step S5 is segmented and inverted to obtain the time series of the absolute thickness of the thin film, which is the final thin film thickness measurement result based on the dispersive confocal sensing principle.

[0012] Furthermore, in step S1, the thin film sample includes an upper interface and a lower interface. The upper interface and the lower interface respectively generate Fresnel reflection and perform dispersive envelope coherent superposition.

[0013] Furthermore, in step S1, the lower interface of the thin film sample is formed by the side surface of the glass substrate facing the thin film sample, constituting a glass-thin film interface, and the upper interface of the thin film sample is a thin film-air interface; the glass-thin film interface also serves as a reference reflector within the sample, and the two reflections generated by the glass-thin film interface and the thin film-air interface are coherently superimposed within the dispersive envelope.

[0014] Furthermore, step S2 applies a predetermined wavelength to the reflectance spectrum of each frame. Centered on, with scale parameter as Peak position detection is performed within the dispersion envelope to obtain the peak position time series. .

[0015] Furthermore, in step S3, the peak time series is processed. High-pass filtering is performed to remove the residue caused by the film thickness. Baseline drift caused by slow changes preserves the thin-film interference phase between the upper and lower interfaces. exist The rapid sawtooth fluctuations generated by the periodic variation and the co-modulation of the peak position by the dispersive envelope; among which For the refractive index of the thin film, Given the geometric thickness of the thin film at time t, the peak position deviation after high-pass filtering is obtained. ;

[0016] Cutoff frequency of high-pass filter satisfy and ,in, The instantaneous time frequency of the thin-film interference phase. The entire data acquisition duration; the cutoff frequency is set to meet the following requirements. .

[0017] Furthermore, step S4 sets the window length of the sliding time window. .

[0018] Furthermore, step S5 establishes a closed-loop mapping between duty cycle and film thickness. The closed mapping is determined by the following parameters: dispersive envelope scale. Pixel-wavelength mapping slope Thin film refractive index upper and lower interface reflectance contrast factor Visible peak threshold With center wavelength Furthermore, closed mappings in intervals The upper part is strictly monotonically increasing, among which The lower critical thickness at which the duty cycle begins to increase from zero. The upper critical thickness is when the duty cycle is close to saturation;

[0019] Closed mapping is caused by phase interference at the upper and lower interfaces of the thin film. Within one phase period, the peak position shift caused by envelope-fringe coupling exceeds [the specified value]. The phase interval length and The ratio is obtained.

[0020] Furthermore, the specific implementation method of step S6 is as follows:

[0021] when Falling into the range At that time, One-dimensional numerical inversion is performed on the closed mapping over the interval to obtain the absolute thickness of the thin film. ,in, and These are the predetermined low-end inversion tolerance and saturation-end inversion tolerance, respectively.

[0022] when When, output The status marker does not output a specific thickness value;

[0023] when When, output The status marker does not output a specific thickness value.

[0024] The beneficial effects of this invention are:

[0025] The thin film thickness measurement method based on the dispersive confocal sensing principle described in this invention can provide the absolute thickness of the thin film from the time series of a single dispersive confocal reflection spectrum within a sliding time window, without relying on external thickness references or leading-edge boundary conditions. The sliding time window covers the thickness range where existing dispersive confocal thin film thickness measurement methods based on peak distance become ineffective when the thin film enters the optical path length region corresponding to the dispersive envelope. Key parameters required for inversion are also included. The known refractive indices of the media on both sides of the interface can be directly given by the Fresnel formula, without the need for additional optical calibration; the inversion result can be used as the initial anchoring thickness for Hilbert phase demodulation, without requiring the film thickness to approach zero or a long-term asymptotic condition; it can be derived from... The time stability in situ determination of whether the flow field satisfies the self-similarity condition of the thin oil film; combined with dual-point synchronous measurement and the thin oil film equation, the wall shear stress can be directly solved, and results can still be given for local measurement scenarios that do not strictly satisfy the self-similarity condition; the present invention can be implemented in the data processing stage of the existing dispersive confocal measurement system. Attached Figure Description

[0026] Figure 1 This is a flowchart of a thin film thickness measurement method based on the dispersive confocal sensing principle described in this invention;

[0027] Figure 2 This is a schematic diagram of the structure of a thin film thickness measurement system based on the dispersive confocal sensing principle according to the present invention.

[0028] Figure 3 For the peak position shift of the dispersive confocal reflectance spectrum and the phase of thin film interference A schematic diagram of the physical image of the relationship, where (a) is =0, the shift of the lower peak position; (b) is = Peak position shift; (c) shows peak position shift as a function of Evolution; (d) is for simulation Sawtooth signal;

[0029] Figure 4 Duty cycle-thickness closed mapping The curve shows the inversion window. With midpoint thickness;

[0030] Figure 5 The measured duty cycle on the measured data of a certain dynamically thinned film Time series and the absolute thickness time series obtained by inversion , where (a) is the measured value. (b) is the time series diagram of the absolute thickness obtained by inversion, and four physical diagnostic diagrams.

[0031] Figure 6 For different initial film thicknesses or different wall shear stress conditions Anchor point moment Comparison chart;

[0032] In the figure, 1 is a broadband light source, 2 is an optical transceiver / coupling module, 3 is a dispersive objective lens, 4 is a thin film, 5 is a glass substrate, 6 is a spectrometer, and 7 is a data processor. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described specific embodiments are merely a part of the embodiments of the invention, and not all of them. The components of the specific embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations, and the invention may also have other embodiments.

[0034] Therefore, the following detailed description of specific embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected specific embodiments of the invention. All other specific embodiments obtained by those skilled in the art based on these specific embodiments without inventive effort are within the scope of protection of this invention.

[0035] To further understand the invention's content, features, and effects, the following specific embodiments are provided, along with accompanying drawings. Figure 1 - Appendix Figure 6 Detailed explanation is as follows:

[0036] Example 1:

[0037] A method for measuring thin film thickness based on the principle of dispersive confocal sensing includes the following steps:

[0038] S1. Dispersive light is projected onto the thin film sample using a dispersive confocal sensor, and the reflection spectra formed by the reflections from the upper and lower interfaces of the thin film sample and their coherent superposition within the same dispersive envelope are continuously collected to obtain the reflection spectrum time series I(p,t), where p is the pixel coordinate of the spectrometer and t is the sampling time.

[0039] Furthermore, in step S1, the thin film sample includes an upper interface and a lower interface. The upper interface and the lower interface respectively generate Fresnel reflection and perform dispersive envelope coherent superposition.

[0040] Furthermore, in step S1, the lower interface of the thin film sample is formed by the side surface of the glass substrate facing the thin film sample, constituting a glass-thin film interface, and the upper interface of the thin film sample is a thin film-air interface; the glass-thin film interface also serves as a reference reflector within the sample, and the two reflections generated by the glass-thin film interface and the thin film-air interface are coherently superimposed within the dispersive envelope.

[0041] S2. The spectrometer performs peak position detection on each frame of reflectance spectrum obtained in step S1 within the dispersion envelope range with preset wavelength and scale parameters to obtain the peak position time series.

[0042] Furthermore, step S2 applies a predetermined wavelength to the reflectance spectrum of each frame. Centered on, with scale parameter as Peak position detection is performed within the dispersion envelope to obtain the peak position time series. .

[0043] S3. For the peak position time series p obtained in step S2 max (t) is high-pass filtered to remove the low-frequency baseline component caused by the slow change in film thickness, resulting in the detrended peak offset Δp(t) = H HP {p max (t)}, the detrended peak shift characterizes the rapid sawtooth fluctuations generated by the co-modulation of the interference phase and dispersive envelope at the upper and lower interfaces of the thin film, where H HP It is a high-pass filter;

[0044] Furthermore, in step S3, the peak time series is processed. High-pass filtering is performed to remove the residue caused by the film thickness. Baseline drift caused by slow changes preserves the thin-film interference phase between the upper and lower interfaces. exist The rapid sawtooth fluctuations generated by the periodic variation and the co-modulation of the peak position by the dispersive envelope; among which For the refractive index of the thin film, Given the geometric thickness of the thin film at time t, the peak position deviation after high-pass filtering is obtained. ;

[0045] Cutoff frequency of high-pass filter satisfy and ,in, The instantaneous time frequency of the thin-film interference phase. The entire data acquisition duration; the cutoff frequency is set to meet the following requirements. .

[0046] S4. Within a sliding time window containing N valid sampling points, the statistics satisfy |Δp(t)|>βσ. e Number of sampling points N e and in accordance with DC obs (t)=N e / N yields the time-varying duty cycle DC obs (t), where β is the dimensionless visible peak threshold, σ e The dispersion envelope scale is expressed in pixels of the spectrometer;

[0047] Furthermore, set the window length of the sliding time window. .

[0048] Furthermore, preferred The threshold value is not less than the background noise of sub-pixel peak detection on the dispersion envelope. The ratio; the window length of the sliding time window. Not less than the thin film interference phase Two changes within this time window The time required for the cycle, i.e. ,in The instantaneous time frequency of the thin-film interference phase; the preferred window length satisfies (That is, the window contains 2 to 20 interference periods), and the sliding step size is the length of the window. to ;

[0049] S5. Establish a closed-form mapping between the time-varying duty cycle obtained in step S4 and the thickness of the thin film sample;

[0050] Furthermore, step S5 establishes a closed-loop mapping between duty cycle and film thickness. The closed mapping is determined by the following parameters: dispersive envelope scale. Pixel-wavelength mapping slope Thin film refractive index upper and lower interface reflectance contrast factor Visible peak threshold With center wavelength Furthermore, closed mappings in intervals The upper part is strictly monotonically increasing, among which The lower critical thickness at which the duty cycle begins to increase from zero. The upper critical thickness is when the duty cycle is close to saturation;

[0051] Closed mapping is caused by phase interference at the upper and lower interfaces of the thin film. Within one phase period, the peak position shift caused by envelope-fringe coupling exceeds [the specified value]. The phase interval length and The ratio is obtained.

[0052] Furthermore, step S5 closed mapping Build as follows:

[0053] Define the dimensionless driving quantity and threshold parameter:

[0054] ;

[0055] ;

[0056] Seeking information about Solution interval of the quadratic inequality ,in:

[0057] ;

[0058] ;

[0059] The duty cycle is given by the following formula (when the discriminant is...) Time to take ):

[0060] ;

[0061] By discriminant condition Uniquely certain; Depend on The only certainty is that among them This is the predetermined saturation tolerance;

[0062] Furthermore, the contrast factor of the upper and lower interfaces. The amplitude reflection coefficients at the upper and lower interfaces of the thin film are calculated using the following formula. , get:

[0063] ;

[0064] The amplitude reflection coefficient is determined by the medium on both sides of the upper and lower interface at the center wavelength. The known refractive index at that point is calculated using the Fresnel formula;

[0065] S6. Based on the time-varying duty cycle obtained in step S4, the closed-form mapping obtained in step S5 is segmented and inverted to obtain the time series of the absolute thickness of the thin film, which is the final thin film thickness measurement result based on the dispersive confocal sensing principle.

[0066] Furthermore, the specific implementation method of step S6 is as follows:

[0067] when Falling into the range At that time, One-dimensional numerical inversion is performed on the closed mapping over the interval to obtain the absolute thickness of the thin film. ,in, and These are the predetermined suppression tolerance and saturation tolerance, respectively;

[0068] when When, output The status marker does not output a specific thickness value;

[0069] when When, output The status marker does not output a specific thickness value.

[0070] Furthermore, suppress tolerance With saturation tolerance The preferred value range is Further optimization ;

[0071] Furthermore, to the absolute thickness time series As the initial anchor for the relative thickness change obtained from Hilbert phase demodulation:

[0072] a) The peak shift sequence obtained in step S3 The analytic signal is obtained by performing a Hilbert transform, and the phase of the analytic signal is unwound to obtain a continuous phase. ; where continuous phase Corresponding to thin film interference phase The cumulative amount;

[0073] b) by Give relative thickness variation ;

[0074] c) Select a closed mapping right The moment when the sensitivity meets the predetermined conditions is used as the anchoring moment. Preferred selection The corresponding time, and the result obtained by inversion at that time. As initial thickness ,according to Reconstruct the time series of film thickness.

[0075] Furthermore, for solutions that satisfy the self-similarity of thin oil films... The flow field defines the empirical diagnostic quantity. ;when When the relative change within the monotonic interval of the closed mapping does not exceed a predetermined threshold, the measured flow field is determined to be descriptive by a self-similar solution; when When it changes monotonically over time, with The time gradient serves as a quantitative diagnostic signal for the flow field's deviation from the self-similarity condition; the predetermined threshold is determined by the confidence level requirement for the measured flow field's self-similarity assessment.

[0076] Furthermore, the thin film is an oil film used for measuring wall friction, and the oil film in The dynamic viscosity is cP to cP, refractive index to The dispersive confocal measurement system receives the reflection spectrum of the oil film during the thinning process under airflow shearing; the time series of the absolute thickness of the film. Used to invert the wall shear stress corresponding to the airflow.

[0077] Furthermore, the thin film is a photoresist film or sacrificial layer film deployed on a substrate in semiconductor photolithography or microelectromechanical system (MEMS) thick-film processes, and the substrate is a silicon or glass substrate with a refractive index of [missing information]. to Thickness range is μm to μm; Dispersion confocal measurement system with sampling rate Hz monitoring of film thickness changes during spin coating, baking, development, or thinning processes; visible peak threshold. With the dispersion envelope scale Select the inversion window Coverage thickness range.

[0078] Furthermore, the thin film is a liquid film flowing along the solid surface, and the refractive index of the liquid film is... to Thickness range is μm to μm; The dispersive confocal measurement system measures the instantaneous local thickness of the liquid film and outputs the absolute thickness time series according to the closed-loop mapping.

[0079] Furthermore, the testing system simultaneously generates at least two spatially separated dispersive focal points A and B, which are projected onto two spatial locations on the thin film sample, respectively. and ,spacing Given that the two dispersive focal points share the same dispersive objective and the same spectrometer channel, and are imaged on the spectrometer in different rows or columns via spatial multiplexing, the absolute thickness time series are obtained independently at the two spatial locations. and The spatial gradient of the film thickness along the surface is obtained by the thickness difference between two points. .

[0080] Further spatial gradient With time derivative of film thickness Substituting into the thin oil film equation:

[0081]

[0082] Solving for wall shear stress ,in For film dynamic viscosity, This represents the pressure above the membrane.

[0083] Furthermore, a glass substrate is placed below the thin film sample. The thickness of the glass substrate is determined by the working distance and dispersion range of the dispersive objective lens, so that the side surface of the glass substrate facing the thin film falls within the effective depth range of the dispersive confocal sensing.

[0084] Example 2:

[0085] Based on Example 1, this embodiment illustrates the method for measuring the absolute thickness of dynamically thinned oil films as follows:

[0086] Step S1 (Optical Path Setup): Set up a dispersive confocal measurement system, including a broadband white light source (such as a halogen lamp, with wavelength range covering...). – nm), hyperchromatic objectives (hyperchromat is a common implementation of hyperchromatic objectives, working distance) – mm, dispersion range matched to the thickness to be measured), receiving optical fiber (its end face serves as a confocal stop), and spectrometer (spectral resolution approximately mm). nm, sampling rate (Hz). The dispersive focal point is projected onto the upper surface of a glass substrate. The measured oil film (oil film refractive index) A thin film sample is formed by drop-coating the sample onto the upper surface of a glass substrate at the test point. The optical path is arranged according to a common optical path self-reference structure. The side of the glass substrate facing the oil film forms the glass-oil film interface, which serves as the internal reference reflector for dispersive confocal sensing. The oil film-air interface is the upper interface of the thin film.

[0087] Furthermore, the optical transceiver / coupling module can employ a beam splitter, fiber coupler, or a common-path single-fiber structure;

[0088] Step S2 (Parameter Predetermination): Based on the optical path and sample parameters, predetermine the following closed-loop mapping inputs:

[0089] Dispersion envelope center wavelength nm;

[0090] Dispersion envelope scale px (corresponding to FWHM) px);

[0091] Pixel-wavelength mapping slope nm / px;

[0092] Thin film refractive index ;

[0093] Upper and lower interface reflectance contrast factor Calculated according to the given Fresnel expression; in this embodiment, we take... exist – The calibration values ​​are within the specified range (the specific values ​​depend on the actual reflective interface state between the glass substrate material and the oil film, and can be determined by the single film thickness calibration before the experiment).

[0094] Visible peak threshold Corresponding threshold px, not less than the measured subpixel peak background of approximately px.

[0095] The inversion window can be calculated from the closed mapping. With midpoint thickness (in the above parameters and) Down μm; in Down μm).

[0096] Step S3 (Data Acquisition): Continuously acquire dispersive confocal reflectance spectra. Sampling rate Hz, continuous duration s.

[0097] Step S4 (Peak Detection): For each frame of spectrum... nearby Subpixel peak detection is performed within the pixel search window. Optional detection methods include detection near the peak. Gaussian fitting, three-point parabolic fitting, or centroid method can be used to fit pixel intensity data; different detection methods do not affect the subsequent definition of duty cycle. This embodiment uses three-point parabolic fitting to obtain the peak position time series. .

[0098] Step S5 (High-pass filtering): Using a Butterworth high-pass filter (order 3, cutoff frequency...) Hz) Filtering yields the detrended peak shift sequence. The selected filter has an approximately linear phase response within the passband to avoid artificially introducing peak shift.

[0099] Step S6 (Sliding window duty cycle statistics): Based on window length s, step size s in Swipe up to view statistics within each window. The sample proportion of px is used as the center time of this window. ,get .

[0100] Step S7 (Closed-loop inversion and piecewise output): From parameters , , , , , Pre-generated Data table coverage range For each window Perform a one-dimensional inversion following the steps below (because...) In logarithm It is nearly linear in scale and converges using the geometric midpoint (or the arithmetic midpoint bisection can be used instead).

[0101] Input: Measured duty cycle ; Inversion window lower and upper bounds , ;quench tolerance ; Saturation tolerance Maximum number of iterations .

[0102] Judgment and initialization:

[0103] 1) If Output status flags ",Finish;

[0104] 2) If Output status flags ",Finish;

[0105] 3) Otherwise set , .

[0106] Iterative process ( ):

[0107] 1) Take the geometric midpoint ;

[0108] 2) Calculated from closed mapping ;

[0109] 3) If ,but ;otherwise .

[0110] Output: .

[0111] Repeat the above steps for each moment of the sliding window to obtain the inversion result. .

[0112] Step S8 (Optional – Hilbert Anchoring and Diagnostic Measures): The peak shift sequence obtained in step S5... Performing a Hilbert transform yields an analytic signal, and unwinding the phase of the analytic signal yields a continuous phase. Continuous phase corresponds to thin-film interference phase. The accumulation. Then by Give the relative thickness variation; select Time for ,correspond Reconstructing the absolute thickness time series . can be The time stability diagnosis determines whether the measured flow field satisfies the thin oil film self-similarity condition: for the Tanner-Blows self-similarity solution of the thin oil film. (See Tanner LH and Blows LG, J. Phys. E: Sci. Instrum. 1976, 9(3): 194-202), fixed measuring points Place Since it is a time invariant, therefore The deviation constant means that the flow field deviates from the self-similar solution.

[0113] Step S9 (Typical Measurement Process): In a typical case, After undergoing three stages of evolution—high-level, mid-level, and low-level quenching—the inversion results can be cross-checked with the independent Hilbert phase demodulation results of the same stage.

[0114] Example 3:

[0115] Based on Example 1, this embodiment illustrates the design process of the inversion window according to the optical path parameters as follows:

[0116] For different application thickness ranges, adjustments can be made. , , Isoparameter translation inversion window As can be seen from the closed expression, , All with Same sign change, and The sign changes. Specifically, it increases. (That is, using a wider dispersive spot) can shift the inversion window as a whole towards a thinner direction; reduce Can be reduced However, it requires a simultaneous reduction in the background noise of peak position detection; and a reduction in the center wavelength. Can reduce at the same time and In practice, the inversion window can be pre-calculated for the parameter combination using a closed expression, and then the set that best matches the range of the film thickness being measured can be selected.

[0117] Example 4:

[0118] Based on Example 1, this embodiment illustrates multi-spatial point synchronous measurement and friction inversion as follows:

[0119] A spatial separation element for the dispersive focal points (such as a tilting mirror assembly or a Wollaston prism derivative configuration) is placed between the dispersive confocal measurement system and the sample, enabling the spectrometer to simultaneously receive the reflection spectra corresponding to two spatially separated dispersive focal points. The two focal points share the same dispersive objective lens and the same spectrometer channel, and are imaged onto different rows or columns of the spectrometer using spatial multiplexing. Spacing Preferred – mm, determined by geometric calibration before the experiment. The values ​​are obtained by inversion of the two beam focal points respectively. , Thus, the spatial gradient is obtained. Thickness time derivative The time difference of the continuous phase obtained from Hilbert phase demodulation is given. Combined with the known pressure gradient... Substitute the solutions into the thin oil film equation to solve for the wall shear stress. The physical basis of the thin oil film equation can be found in publicly available literature such as Naughton & Sheplak (Prog. Aerosp. Sci. 2002, 38: 515).

[0120] Example 5:

[0121] This embodiment, based on Embodiment 1, illustrates the monitoring process of the photolithography spin coating process as follows: The dispersion confocal measurement system of this invention is arranged above the turntable of the photolithography spin coating equipment, vertically aligned with the center of the substrate, which is a silicon or glass substrate. During spin coating, baking, and development processes, the monitoring process is performed at a sampling rate... Continuous acquisition of the reflectance spectrum at Hz. When the photoresist thickness is 12... – When selecting the μm range , Make the inversion window Covering this range. Example: Refractive index of photoresist. , nm px、 nm / px, (The upper interface of the photoresist is exposed to air, and the lower interface is exposed to the silicon substrate.) , calculate – μm; if it is necessary to move the inversion window down to cover a thinner photoresist, the size can be reduced. or reduce .

[0122] Example 6:

[0123] Based on Example 1, this embodiment illustrates the process of measuring the local thickness of a liquid film during flow as follows:

[0124] In the liquid film flow experiment, the dispersive confocal measurement system is positioned above the wall surface to be measured, with the dispersive focus projected onto the liquid film surface. When the liquid film thickness is 13... – For the μm range, the absolute thickness time series is given according to this invention. Example: For the refractive index of the liquid film... , nm px、 , The inversion window is calculated to be approximately – μm, covering the typical application range of water-based liquid membranes.

[0125] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0126] Although this application has been described above with reference to specific embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the features in the specific embodiments disclosed in this application can be combined with each other in any way. The lack of an exhaustive description of these combinations in this specification is merely for the sake of brevity and resource conservation. Therefore, this application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for measuring thin film thickness based on the principle of dispersive confocal sensing, characterized in that, Includes the following steps: S1. Dispersive light is projected onto the thin film sample using a dispersive confocal sensor, and the reflection spectra formed by the reflections from the upper and lower interfaces of the thin film sample and their coherent superposition within the same dispersive envelope are continuously collected to obtain the reflection spectrum time series I(p,t), where p is the pixel coordinate of the spectrometer and t is the sampling time. S2. The spectrometer performs peak position detection on each frame of reflectance spectrum obtained in step S1 within the dispersion envelope range with preset wavelength and scale parameters to obtain the peak position time series. S3. For the peak position time series p obtained in step S2 max (t) is high-pass filtered to remove the low-frequency baseline component caused by the slow change in film thickness, resulting in the detrended peak offset Δp(t) = H HP {p max (t)}, the detrended peak shift characterizes the rapid sawtooth fluctuations generated by the co-modulation of the interference phase and dispersive envelope at the upper and lower interfaces of the thin film, where H HP It is a high-pass filter; S4. Within a sliding time window containing N valid sampling points, the statistics satisfy |Δp(t)|>βσ. e Number of sampling points N e and in accordance with DC obs (t)=N e / N yields the time-varying duty cycle DC obs (t), where β is the dimensionless visible peak threshold, σ e The dispersion envelope scale is expressed in pixels of the spectrometer; S5. Establish a closed-form mapping between the time-varying duty cycle obtained in step S4 and the thickness of the thin film sample; S6. Based on the time-varying duty cycle obtained in step S4, the closed-form mapping obtained in step S5 is segmented and inverted to obtain the time series of the absolute thickness of the thin film, which is the final thin film thickness measurement result based on the dispersive confocal sensing principle.

2. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 1, characterized in that, In step S1, the thin film sample includes an upper interface and a lower interface. The upper and lower interfaces generate Fresnel reflections and perform dispersive envelope coherent superposition.

3. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 2, characterized in that, In step S1, the lower interface of the thin film sample is formed by the side surface of the glass substrate facing the thin film sample, constituting a glass-thin film interface, and the upper interface of the thin film sample is a thin film-air interface. The glass-film interface also serves as an intrasample reference reflector, and the two reflections generated by the glass-film interface and the film-air interface coherently superimpose within the dispersive envelope.

4. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 3, characterized in that, Step S2 applies the reflectance spectrum of each frame to a predetermined wavelength. Centered on, with scale parameter as Peak position detection is performed within the dispersion envelope to obtain the peak position time series. .

5. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 4, characterized in that, In step S3, the peak time series is processed. High-pass filtering is performed to remove the residue caused by the film thickness. Baseline drift caused by slow changes preserves the thin-film interference phase between the upper and lower interfaces. exist The rapid sawtooth fluctuations generated by the periodic variation and the co-modulation of the peak position by the dispersive envelope; among which For the refractive index of the thin film, Given the geometric thickness of the thin film at time t, the peak position deviation after high-pass filtering is obtained. ; Cutoff frequency of high-pass filter satisfy and ,in, The instantaneous time frequency of the thin-film interference phase. The entire data acquisition duration; the cutoff frequency is set to meet the following requirements. .

6. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 5, characterized in that, Step S4: Set the window length of the sliding time window. .

7. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 6, characterized in that, Step S5 establishes a closed mapping between duty cycle and film thickness. The closed mapping is determined by the following parameters: dispersive envelope scale. Pixel-wavelength mapping slope thin film refractive index upper and lower interface reflectance contrast factor Visible peak threshold With center wavelength ; Furthermore, closed mappings in intervals The upper part is strictly monotonically increasing, among which The lower critical thickness at which the duty cycle begins to increase from zero. The upper critical thickness is when the duty cycle is close to saturation; Closed mapping is caused by phase interference at the upper and lower interfaces of the thin film. Within one phase period, the peak position shift caused by envelope-fringe coupling exceeds [the specified value]. The phase interval length and The ratio is obtained.

8. The thin film thickness measurement method based on the dispersive confocal sensing principle according to claim 7, characterized in that, The specific implementation method of step S6 is as follows: when Falling into the range At that time, One-dimensional numerical inversion is performed on the closed mapping over the interval to obtain the absolute thickness of the thin film. ,in, and These are the predetermined low-end inversion tolerance and saturation-end inversion tolerance, respectively. when When, output The status marker does not output a specific thickness value; when When, output The status marker does not output a specific thickness value.

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