Thickness measurement method based on overlapping peak signal decomposition

Abstract

The present invention proposes a thickness measurement method based on the decomposition of overlapping peak signals, collects the light intensity of the pre-focus and post-focus photodetectors and the focusing lens displacement corresponding to the light intensity, obtains the decomposed light intensity signal through algorithm iteration and update, obtains the zero-crossing position information of the differential confocal signal curve according to the decomposed light intensity signal, and then obtains the thickness of the object to be measured. The thickness measurement method provided by the present invention can achieve accurate measurement of micron-level thickness films only through algorithms without any additional optical elements, and expands the measurement range and application occasions of the differential confocal measurement system. It solves the technical problem that when the thickness of the object to be measured is too small, the differential signals of the light intensity of the upper and lower surfaces are superimposed on each other, and the thickness of the object to be measured at the micron level cannot be measured.

Description

Technical Field

[0001] The invention relates to the technical field of optical detection, and in particular to a thickness measurement method based on overlapping peak signal decomposition. Background Art

[0002] Thickness is one of the most widely used parameters related to length, and it is defined as the distance between the top and bottom or the front and back of an object with parallel sides. Thickness measurement is required in various research and industrial fields, such as automotive, shipbuilding, aviation, nanotechnology, and biotechnology. With the advent of the fourth industrial revolution, the demand for thickness measurement in the semiconductor and display industries has steadily increased. For example, when manufacturing smart semiconductor devices, the physical thickness of various layers such as substrates and films should be monitored and controlled to ensure performance. According to the detection conditions such as the material properties and shape of the sample, the thickness range, and the degree of measurement accuracy, different types of thickness measurement methods have been proposed and implemented for thickness measurement in different applications. Thickness measurement methods can be simply divided into contact and non-contact methods. In recent years, non-contact measurement methods have attracted widespread attention due to their practical advantages of non-destructive testing and non-destructive measurement. Non-contact methods are divided into optical methods and non-optical methods.

[0003] Laser differential confocal microscopy is an emerging technology among existing non-contact optical methods. Laser differential confocal microscopy has the advantages of absolute measurement and focus tracking, which can improve focus sensitivity, sensor linearity and signal-to-noise ratio.

[0004] However, the laser differential confocal microscopy technology in the prior art is aimed at measuring the central thickness of optical lenses, and the thickness of such measured objects is often in the order of centimeters and millimeters. When using a differential confocal sensor to measure the thickness of a micron-level measured object such as a film or a glass slide, the intersection or superposition of the two sub-reflection intensity distributions will cause the differential confocal response signal to be inaccurate, that is, the differential signals of the upper and lower surfaces of the measured object are superimposed on each other, and the upper and lower surface positions of the measured object cannot be directly obtained through the zero crossing of the differential signal, which affects the measurement accuracy of the measured object thickness and even leads to the technical problem that the measurement result cannot be obtained. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and propose a thickness measurement method based on overlapping peak signal decomposition.

[0006] To achieve the above object, the present invention adopts the following specific technical solutions:

[0007] A thickness measurement method based on overlapping peak signal decomposition, the thickness measurement method comprising the following steps:

[0008] S1, respectively collecting light intensity data of the pre-focus photodetector and the post-focus photodetector in the differential confocal measurement system, as well as the displacement value of the focusing lens corresponding to the light intensity data;

[0009] S2. Calculate the centroid of the light beam received by the pre-focus photodetector and the post-focus photodetector respectively according to the pre-focus light intensity data and the post-focus light intensity data;

[0010] S3, based on the centroid, decomposing the pre-focus light intensity data and the post-focus light intensity data into initial light intensity data reflected from the upper surface and the lower surface of the object to be tested, respectively;

[0011] S4, based on the first preset condition, iteratively update the initial light intensity data reflected by the upper surface and the initial light intensity data reflected by the lower surface of the object to be tested, respectively, and calculate the centroid of the iteratively updated light intensity data, and determine whether to stop the iterative update according to the second preset condition, and obtain the decomposed light intensity data of the upper surface and the lower surface of the object to be tested and the corresponding centroid data;

[0012] S5, obtaining zero-crossing point position information of the differential confocal signal curves of the upper surface and the lower surface of the object to be tested respectively according to the decomposed light intensity data reflected from the upper surface and the lower surface of the object to be tested;

[0013] S6. Calculate the thickness of the object to be measured according to the zero-crossing point position information.

[0014] Furthermore, in step S2, the calculation formula (1) for the centroid of the light beam received by the pre-focus photodetector and the post-focus photodetector is specifically:

[0015]

[0016] Among them, u c represents the center of mass; I(u) represents the light intensity data of the pre-focus photodetector or the post-focus photodetector; u represents the displacement value of the focusing lens movement corresponding to the light intensity data.

[0017] Furthermore, in step S3, the light intensity data is decomposed according to formula (2):

[0018]

[0019] Among them, I up 1 (u) represents the initial light intensity data reflected from the surface of the object to be tested by the pre-focus photodetector or the post-focus photodetector; I down 1 (u) represents the initial light intensity data reflected from the lower surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector.

[0020] Furthermore, the step S4 is specifically as follows:

[0021] S401, iteratively update the initial light intensity data according to a first preset condition, and calculate the centroid of the iteratively updated light intensity data, wherein the formula (3) for iteratively updating the first preset condition is specifically:

[0022]

[0023] Wherein, α represents the half-peak width of the single-peak signal of the light intensity signal reflected from the upper or lower surface of the object to be tested; represents the light intensity data reflected from the upper surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the m-th iteration update; represents the light intensity data reflected from the lower surface of the object to be tested by the pre-focus photodetector or the post-focus photodetector during the m-th iteration update; represents the light intensity data reflected from the upper surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the (m+1)th iterative update; represents the light intensity data reflected from the lower surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the m+1th iteration update; m is the number of iterations, and the initial value is set to 1; Represents the centroid of the upper surface light intensity data at the mth iteration update; The centroid of the lower surface light intensity data during the mth iteration update;

[0024] S402, judging whether the second preset condition is met, if not, continuing the iterative update; if the second preset condition is met, stopping the iterative update, and obtaining the light intensity data of the upper surface and the light intensity data of the lower surface of the decomposed object to be measured; the second preset condition is specifically formula (4):

[0025]

[0026] Here, ε represents the iteration stop parameter.

[0027] S403, obtaining the light intensity data on the upper surface of the decomposed object to be tested: The light intensity data of the lower surface of the object to be tested is: As well as the centroid data corresponding to the light intensity data on the upper and lower surfaces of the object to be tested.

[0028] Furthermore, the step S5 is specifically as follows:

[0029] S501, subtract the light intensity data reflected by the upper surface of the object to be tested from the pre-focus photodetector and the post-focus photodetector after decomposition to obtain a differential confocal characteristic curve of the upper surface of the object to be tested; subtract the light intensity data reflected by the lower surface of the object to be tested from the pre-focus photodetector and the post-focus photodetector after decomposition to obtain a differential confocal characteristic curve of the lower surface of the object to be tested;

[0030] S502 , respectively obtaining zero-crossing point position information of the differential confocal signal curves on the upper surface and the lower surface of the object to be measured.

[0031] Furthermore, the formula (5) for calculating the thickness of the object to be measured in step S6 is specifically:

[0032]

[0033] Where thickness represents the thickness of the object to be measured; u up Indicates the zero-crossing position information of the differential confocal signal curve on the surface of the object to be measured; u down It represents the zero-crossing position information of the differential confocal signal curve on the lower surface of the object to be measured; θ represents the aperture angle of the focusing lens; and n represents the refractive index of the object to be measured.

[0034] The thickness measurement method based on overlapping peak signal decomposition provided by the present invention can be applied to the existing differential confocal measurement system, and the differential signals of the upper and lower surfaces of the object to be measured are decomposed into the light intensity signal of the upper surface of the object to be measured by the pre-focus photodetector, the light intensity signal of the lower surface of the object to be measured by the pre-focus photodetector, the light intensity signal of the upper surface of the object to be measured by the post-focus photodetector, and the light intensity signal of the lower surface of the object to be measured by the post-focus photodetector, and the inter-class variance function of the decomposed light intensity data is minimized by the algorithm, thereby achieving the purpose of the difference between the decomposed signal and the real signal, and improving the accuracy of the thickness measurement method. The zero-crossing point position information of the differential confocal signal curve is obtained according to the decomposed light intensity signal, and then the thickness of the object to be measured is obtained. The embodiment of the present invention realizes the accurate measurement of micron-level thickness films only through the algorithm without any additional optical elements, and expands the measurement range and application occasions of the differential confocal measurement system. It solves the technical problem that when the thickness of the object to be measured is too small, the differential signals of the light intensity of the upper and lower surfaces are superimposed on each other, and the thickness of the object to be measured at the micron level cannot be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a schematic diagram of a differential confocal measurement system according to an embodiment of the present invention;

[0036] Figure 2 is a flow chart of a thickness measurement method based on overlapping peak signal decomposition according to an embodiment of the present invention.

[0037] Reference numerals include:

[0038] Laser light source 1, collimating lens 2, first beam splitter 3, focusing lens 4, object to be measured 5, second beam splitter 6, pre-focus focusing lens 7, pre-focus pinhole 8, pre-focus photoelectric detector 9, post-focus focusing lens 10, post-focus pinhole 11, post-focus photoelectric detector 12. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0040] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0041] The specific working mode of the present invention is described in detail below with reference to the accompanying drawings:

[0042] In order to explain the embodiments of the present invention in detail, the differential confocal measurement system in the prior art is described in detail. The differential confocal measurement system used in the embodiments of the present invention is as follows: Figure 1 As shown, it includes a laser light source 1, a collimator 2, a first beam splitter 3, a focusing lens 4, a second beam splitter 6, a pre-focus focusing lens 7, a pre-focus pinhole 8, a pre-focus photodetector 9, a post-focus focusing lens 10, a post-focus pinhole 11, a post-focus photodetector 12, an interferometer, and a transmission assembly arranged in sequence along the optical path. The transmission assembly used in the embodiment of the present invention is an objective lens positioner. The transmission assembly is fixedly connected to the focusing lens 4, and the transmission assembly controls the focusing lens 4 to move back and forth at a uniform speed along the direction of the laser beam to control the imaging position of the surface of the object to be measured, that is, the focal position. The interferometer is used to measure the displacement value of the focusing lens 4. In the embodiment of the present invention, the displacement range of the transmission assembly is 400μm, and the measurement accuracy of the interferometer is 0.5nm. The laser light source 1 emits a laser beam, which is collimated by the collimator 2 and then incident on the first beam splitter 3 for beam splitting. The transmitted light beam transmitted by the first beam splitter 3 is focused by the focusing lens 4 and then incident on the object to be measured 5. After being reflected by the object to be measured 5, it returns along the original optical path and is reflected by the first beam splitter 3 to the second beam splitter 6 for beam splitting. The light beam transmitted by the second beam splitter 6 is used as the pre-focus light beam, which is incident on the pre-focus photodetector 9 via the pre-focus focusing lens 7 and the pre-focus pinhole 8 in sequence. The light beam reflected by the second beam splitter 6 is used as the post-focus light beam, which is incident on the post-focus photodetector 12 via the post-focus focusing lens 10 and the post-focus pinhole 11 in sequence.

[0043] The light intensity data of the pre-focus photoelectric detector 9 and the post-focus photoelectric detector 12 are collected and recorded as I(u, -u m ) and I(u, +u m The light intensity data of the pre-focus photodetector 9 is subtracted from the light intensity data of the post-focus photodetector 12 to obtain the differential confocal signal curve FES = I(u, -u m )-I(u,+u m ), and obtain the differential signal data of the differential confocal signal curve. When the laser beam is focused on the surface of the object to be measured 5, the light intensity received by the pre-focus photodetector 9 and the post-focus photodetector 12 is equal. The position of the focusing lens 4 is recorded as u by the interferometer, that is, the displacement value of the focusing lens 4 corresponding to the zero-crossing position measured by the interferometer is u, and the position information u of the surface of the object to be measured 5 is obtained. Among them, FES represents the differential confocal characteristic curve, u m represents the defocus amount, and u represents the position information of the point to be measured on the surface of the object to be measured 5.

[0044] The thickness measurement method provided by the present invention can be applied to different differential confocal measurement systems in the prior art. Therefore, the differential confocal measurement system may have other forms of changes, which shall be subject to actual usage. The present invention is not limited to this, and only gives examples to explain the embodiments of the present invention in detail.

[0045] In the process of measuring the thickness of the object 5 to be measured, the differential confocal measurement system usually obtains the positions of the upper and lower surfaces of the object 5 to be measured by obtaining the differential signal of the object 5 to be measured, and then measures its thickness. However, when the thickness of the object 5 to be measured is too small, the differential signals of the light intensity of the upper and lower surfaces of the object 5 to be measured are superimposed on each other, which will make it impossible to directly obtain the positions of the upper and lower surfaces of the object 5 to be measured through the zero point of the differential signal. Therefore, the measurement method of the embodiment of the present invention is to decompose the light intensity data collected by the pre-focus photodetector 9 and the post-focus photodetector 12 into the light intensity signal reflected from the upper surface and the light intensity signal reflected from the lower surface, and the decomposed light intensity signal satisfies: the inter-class variance function obtains the minimum value. In addition, the difference between the signal decomposed by the technical solution of the present invention and the real signal is minimized, thereby improving the accuracy of thickness measurement.

[0046] The embodiment of the present invention provides a thickness measurement method based on overlapping peak signal decomposition, and the method flow chart is as follows: Figure 2 shown.

[0047] S1, respectively collect the light intensity data I(u, -u) of the front-focus photodetector 9 in the differential confocal measurement system m ) and the light intensity data I(u, +u m ), and the displacement value u of the focusing lens 4 corresponding to the light intensity data.

[0048] In the process of measuring the thickness of the object 5, since both the upper and lower surfaces of the object 5 reflect the incident light beam, the light intensity data received by the pre-focus photodetector 9 and the post-focus photodetector 12 can be regarded as the superposition of the light intensity signal reflected from the upper surface and the light intensity signal reflected from the lower surface of the object 5, as shown in formula (1):

[0049]

[0050] Among them, I(u,-u m ) represents the light intensity data of the pre-focus photodetector 9; I(u, +u m ) represents the light intensity data of the post-focus photodetector 12; I cf-up (u,-u m ) represents the light intensity data on the surface of the pre-focus photodetector 9; I cf-down (u,-u m ) represents the light intensity data of the lower surface of the pre-focus photodetector 9; I cb-up (u,+u m ) represents the light intensity data on the surface of the post-focus photodetector 12; I cb-down (u,+u m ) represents the light intensity data of the lower surface of the post-focus photodetector 12.

[0051] S2, the pre-focus light intensity data I(u, -u m ) and the post-focus light intensity data I(u, +u m ), and substitute into formula (2) and formula (3) respectively to calculate the centroid of the light beam received by the pre-focus photodetector 9 and the post-focus photodetector 12; the calculation formulas (2) and (3) for the centroid of the light beam received by the pre-focus photodetector 9 and the post-focus photodetector 12 are specifically:

[0052]

[0053] Among them, u cf represents the center of mass of the pre-focus photodetector 9; u cb represents the centroid of the pre-focus photodetector 9; u represents the displacement value of the focusing lens 4 corresponding to the light intensity data.

[0054] In the embodiment of the present invention, the centroid calculation method can be calculated using the common centroid algorithm, enhanced weighted centroid algorithm, threshold centroid algorithm and other methods in the prior art. The present invention does not limit this and can be selected according to actual conditions.

[0055] S3. Based on the calculated centroid, the pre-focus light intensity data and the post-focus light intensity data are decomposed according to formulas (4) and (5) respectively into initial light intensity data reflected from the upper surface and the lower surface of the object 5 to be tested.

[0056] The formula (4) for decomposing the pre-focus light intensity data is as follows:

[0057]

[0058] The formula (5) for decomposing the post-focus light intensity data is as follows:

[0059]

[0060] Among them, I cf-up 1 (u,-u m ) represents the initial light intensity data reflected from the upper surface of the object 5 to be tested by the pre-focus photodetector 9; I cf-down 1 (u,-u m ) represents the initial light intensity data reflected by the lower surface of the object 5 under test from the pre-focus photodetector 9; I cb-up 1 (u,+u m ) represents the initial light intensity data reflected from the upper surface of the object 5 to be tested by the post-focus photodetector 12; I cb-down 1 (u,+u m ) represents the initial light intensity data reflected by the lower surface of the object 5 to be tested by the post-focus photodetector 12.

[0061] S4. Based on the first preset condition, the initial light intensity data reflected on the upper surface and the initial light intensity data reflected on the lower surface of the object to be tested 5 obtained in step S3 by the pre-focus photodetector 9 and the post-focus photodetector 12 are iteratively updated respectively, and the centroid of the iteratively updated light intensity data is calculated. According to the second preset condition, it is determined whether to stop the iterative update, and the light intensity data of the upper and lower surfaces of the object to be tested 5 after decomposition are obtained.

[0062] S401. According to a first preset condition, the initial light intensity data is iteratively updated using formulas (6) and (7), and the centroid of the iteratively updated light intensity data is calculated.

[0063] The iterative update formula (6) of the first preset condition of the pre-focus photodetector 9 is specifically:

[0064]

[0065] The iterative update formula (7) of the first preset condition of the post-focus photodetector 12 is specifically:

[0066]

[0067] Wherein, α represents the half-peak width of the single-peak signal of the light intensity signal reflected from the upper or lower surface of the object to be measured 5; represents the light intensity data reflected from the upper surface of the object 5 to be tested by the pre-focus photodetector 9 during the m-th iteration update; represents the light intensity data reflected by the lower surface of the object 5 to be tested of the pre-focus photodetector 9 during the m-th iteration update; represents the light intensity data reflected from the upper surface of the object 5 to be tested by the post-focus photodetector 12 during the m-th iteration update; represents the light intensity data reflected from the lower surface of the object 5 to be tested by the post-focus photodetector 12 during the m-th iteration update; represents the light intensity data reflected from the upper surface of the object 5 to be tested by the pre-focus photodetector 9 during the (m+1)th iteration update; represents the light intensity data reflected from the upper surface of the object 5 to be tested by the pre-focus photodetector 9 during the (m+1)th iteration update; represents the light intensity data reflected from the upper surface of the object 5 to be tested by the post-focus photoelectric detector 12 during the (m+1)th iteration update; represents the light intensity data reflected from the lower surface of the object 5 to be tested by the post-focus photoelectric detector 12 during the m+1th iteration update; m is the number of iterations, and the initial value is set to 1; Represents the centroid of the upper surface light intensity data at the mth iteration update; The centroid of the lower surface light intensity data during the mth iteration update.

[0068] In the embodiment of the present invention, the method for obtaining α, that is, the method for obtaining the single peak signal, can be obtained by measuring the plane reflector with a photoelectric detector. The present invention is not limited to this, and other methods in the prior art can also be used to obtain it, which can be selected according to actual conditions.

[0069] S402, judging whether the second preset condition is met, that is, calculating whether the iteratively updated light intensity data of the pre-focus photodetector 9 and the post-focus photodetector 12 are less than the iteration stop parameter by using formula (8) and formula (9) respectively. If the second preset condition is not met, continue to use formula (6) and / or formula (7) for iterative update; if the second preset condition is met, stop iterative update, and obtain the light intensity data of the upper surface and the light intensity data of the lower surface of the decomposed object 5.

[0070] The second preset condition for iterative updating of the pre-focus photoelectric detector 9 is formula (8):

[0071]

[0072] The second preset condition for iterative updating of the post-focus photoelectric detector 12 is formula (9):

[0073]

[0074] Wherein, ε represents the iteration stop parameter. In the embodiment of the present invention, ε is set to 1e -18 If ε is set too large or too small, the zero-crossing position accuracy of the differential confocal characteristic curve obtained after decomposition will be reduced. It can be set according to actual conditions.

[0075] In the embodiment of the present invention, the light intensity data of the pre-focus photodetector 9 and the post-focus photodetector 12 may be different in the calculated number of iterative updates of the pre-focus photodetector 9 and the number of iterative updates of the post-focus photodetector 12, taking into account the influence of equipment installation and environmental factors.

[0076] In the embodiment of the present invention, according to the second preset condition, the light intensity data of the upper surface and the light intensity data of the lower surface of the object to be tested 5 obtained after decomposition satisfy formula (10) and formula (11), that is, the light intensity data of the upper surface and the light intensity data of the lower surface of the object to be tested 5 obtained after decomposition can make the inter-class variance function obtain the minimum value. The inter-class variance function obtains the minimum value, which can make the shapes of the two single-peak signals of the decomposed light intensity signal have the minimum difference compared with the real signal.

[0077] The formula (10) of the pre-focus photodetector 9 and the formula (11) of the post-focus photodetector 12 are specifically:

[0078]

[0079]

[0080] S403, obtaining the light intensity data of the upper surface of the object 5 to be tested of the photoelectric detector 9 after decomposition and before focus: cf-up (u,-u m ); the light intensity data of the lower surface of the object 5 under the focal photodetector 9 is: I cf-down (u,-u m ); the light intensity data of the upper surface of the object to be tested 5 after focusing the photodetector 12 is: I cb-up (u,+u m ); the light intensity data of the lower surface of the object to be tested 5 after focusing the photodetector 12 is: I cb-down (u,+u m ).

[0081] In the embodiment of the present invention, the number of iterative updates of the pre-focus photodetector 9 and the number of iterative updates of the post-focus photodetector 12 are the same, both m+1 times. That is, the light intensity data of the upper surface of the object 5 to be measured obtained by the pre-focus photodetector 9 after decomposition is: The light intensity data of the lower surface of the object 5 to be tested of the pre-focus photodetector 9 is: The light intensity data of the upper surface of the object 5 to be tested by the post-focus photodetector 12 is: The light intensity data of the lower surface of the object 5 to be tested of the post-focus photodetector 12 is:

[0082] S5. Obtain zero-crossing point position information of the differential confocal signal curves of the upper surface and the lower surface of the object to be tested 5 respectively according to the decomposed light intensity data reflected from the upper surface and the lower surface of the object to be tested 5 .

[0083] S501, subtract the light intensity data reflected from the upper surface of the object 5 to be tested by the decomposed pre-focus photodetector 9 and the post-focus photodetector 12, and obtain a differential confocal characteristic curve of the upper surface of the object 5 to be tested; subtract the light intensity data reflected from the lower surface of the object 5 to be tested by the decomposed pre-focus photodetector 9 and the post-focus photodetector 12, and obtain a differential confocal characteristic curve of the lower surface of the object 5 to be tested. The formula (12) of the differential confocal characteristic curve is specifically:

[0084]

[0085] Among them, FES up It represents the differential confocal characteristic curve of the upper surface of the object to be measured 5; FES down It represents the differential confocal characteristic curve of the lower surface of the object 5 to be measured.

[0086] S502, respectively obtain zero-crossing point position information u of the differential confocal signal curve on the upper surface of the object to be measured 5 up , and the zero-crossing position information u of the differential confocal signal curve on the lower surface of the object 5 to be measured down .

[0087] Among them, u up Indicates the zero-crossing position information of the differential confocal signal curve on the upper surface of the object to be measured 5; u down Indicates the zero-crossing point position information of the differential confocal signal curve on the lower surface of the object to be measured 5.

[0088] In the embodiment of the present invention, the method for calculating the zero-crossing point position is a linear interval fitting method, and other methods in the prior art may also be used for calculation. The present invention does not limit this and may be selected according to actual conditions.

[0089] S6. Calculate the thickness of the object 5 according to the zero-crossing point position information. The formula (13) for calculating the thickness of the object 5 is:

[0090]

[0091] Wherein, thickness represents the thickness of the object 5 to be measured; θ represents the aperture angle of the focusing lens 4; and n represents the refractive index of the object 5 to be measured.

[0092] The thickness measurement method based on overlapping peak signal decomposition provided by the present invention can be applied to the existing differential confocal measurement system, decomposing the light intensity signal of the superposition of the upper surface reflection and the lower surface reflection of the object to be measured, collecting the light intensity of the photoelectric detector before and after focus and the focusing lens displacement corresponding to the light intensity, obtaining the decomposed light intensity signal through algorithm iteration update, obtaining the zero-crossing position information of the differential confocal signal curve according to the decomposed light intensity signal, and then obtaining the thickness of the object to be measured. The embodiment of the present invention realizes the accurate measurement of micron-level thickness films only through algorithms without any additional optical elements, and expands the measurement range and application occasions of the differential confocal measurement system. It solves the technical problem that when the thickness of the object to be measured is too small, the differential signals of the light intensity of the upper and lower surfaces are superimposed on each other, and the thickness of the object to be measured with micron-level thickness cannot be measured.

[0093] The embodiment of the present invention verifies the effectiveness of the thickness measurement method of the technical solution of the present invention through experiments. The system parameters of the selected differential confocal measurement system are as follows: the wavelength of the laser light source 1 is 642nm, and after being collimated by the collimator 2, the collimation is a Gaussian collimated beam with a radius of 3.2mm. The focusing lens 4 uses a microscope with a focal length of 9mm, and the refractive index of the object to be measured 5 is 1.51. The pre-focus focusing lens 7 and the post-focus focusing lens 10 use a plano-concave lens with a focal length of 10mm, the pre-focus pinhole 8 and the post-focus pinhole 11 have an offset of 650μm, and the pinhole size is 20μm.

[0094] Table 1 shows the thickness of the object to be measured and the true thickness of the object to be measured by the thickness measurement method of the technical solution of the present invention. The true thickness of the object to be measured is measured using a step meter with a resolution of 0.1nm. Five groups of measurement experiments were conducted using five objects of different thicknesses. The results are as follows:

[0095] Table 1

[0096] Serial number True thickness Technical solution of the present invention 1 3.527μm 3.541μm 2 4.971μm 4.962μm 3 8.532μm 8.525μm 4 12.012μm 12.014μm 5 16.294μm 16.298μm

[0097] By using the thickness measurement method provided by the technical solution of the present invention, the measurement accuracy error of the object to be measured with a thickness of more than 5 μm is within 10 nm.

[0098] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0099] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0100] The above specific implementations of the present invention do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A thickness measurement method based on overlapping peak signal decomposition, It is characterized in that The thickness measurement method comprises the following steps: S1, respectively collecting light intensity data of the pre-focus photodetector and the post-focus photodetector in the differential confocal measurement system, as well as the displacement value of the focusing lens corresponding to the light intensity data; S2. Calculate the centroid of the light beam received by the pre-focus photodetector and the post-focus photodetector respectively according to the pre-focus light intensity data and the post-focus light intensity data; the calculation formula (1) of the centroid of the light beam received by the pre-focus photodetector and the post-focus photodetector is specifically: Among them, u c represents the center of mass; I(u) represents the light intensity data of the pre-focus photodetector or the post-focus photodetector; u represents the displacement value of the focusing lens movement corresponding to the light intensity data; S3. Based on the centroid, decompose the pre-focus light intensity data and the post-focus light intensity data into initial light intensity data reflected from the upper surface and the lower surface of the object to be tested, respectively; decompose the light intensity data according to formula (2): Among them, I up 1 (u) represents the initial light intensity data reflected from the surface of the object to be tested by the pre-focus photodetector or the post-focus photodetector; I down 1 (u) represents the initial light intensity data reflected from the lower surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector; S4, based on the first preset condition, iteratively update the initial light intensity data reflected by the upper surface and the initial light intensity data reflected by the lower surface of the object to be tested, respectively, and calculate the centroid of the iteratively updated light intensity data, and determine whether to stop the iterative update according to the second preset condition, and obtain the decomposed light intensity data of the upper surface and the lower surface of the object to be tested and the corresponding centroid data; S401, iteratively update the initial light intensity data according to a first preset condition, and calculate the centroid of the iteratively updated light intensity data, wherein the formula (3) for iteratively updating the first preset condition is specifically: Wherein, α represents the half-peak width of the single-peak signal of the light intensity signal reflected from the upper or lower surface of the object to be tested; represents the light intensity data reflected from the upper surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the m-th iteration update; represents the light intensity data reflected from the lower surface of the object to be tested by the pre-focus photodetector or the post-focus photodetector during the m-th iteration update; represents the light intensity data reflected from the upper surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the (m+1)th iterative update; represents the light intensity data reflected from the lower surface of the object to be measured by the pre-focus photodetector or the post-focus photodetector during the m+1th iteration update; m is the number of iterations, and the initial value is set to 1; Represents the centroid of the upper surface light intensity data at the mth iteration update; The centroid of the lower surface light intensity data during the mth iteration update; S402, judging whether the second preset condition is met, if not, continuing the iterative update; if the second preset condition is met, stopping the iterative update, and obtaining the light intensity data of the upper surface and the light intensity data of the lower surface of the decomposed object to be measured; the second preset condition is specifically formula (4): Among them, ε represents the iteration stop parameter; S403, obtaining the light intensity data on the upper surface of the decomposed object to be tested: The light intensity data of the lower surface of the object to be tested is: and obtaining centroid data corresponding to the light intensity data of the upper surface and the lower surface of the object to be tested; S5, obtaining zero-crossing point position information of the differential confocal signal curves of the upper surface and the lower surface of the object to be tested respectively according to the decomposed light intensity data reflected from the upper surface and the lower surface of the object to be tested; S6. Calculate the thickness of the object to be measured according to the zero-crossing point position information.

2. The thickness measurement method according to claim 1, It is characterized in that The step S5 is specifically as follows: S501, subtract the light intensity data reflected by the upper surface of the object to be tested from the pre-focus photodetector and the post-focus photodetector after decomposition to obtain a differential confocal characteristic curve of the upper surface of the object to be tested; subtract the light intensity data reflected by the lower surface of the object to be tested from the pre-focus photodetector and the post-focus photodetector after decomposition to obtain a differential confocal characteristic curve of the lower surface of the object to be tested; S502 , respectively obtaining zero-crossing point position information of the differential confocal signal curves on the upper surface and the lower surface of the object to be measured.

3. The thickness measuring method according to claim 2, It is characterized in that The formula (5) for calculating the thickness of the object to be measured in step S6 is specifically: Where thickness represents the thickness of the object to be measured; u up Indicates the zero-crossing position information of the differential confocal signal curve on the surface of the object to be measured; u down It represents the zero-crossing position information of the differential confocal signal curve on the lower surface of the object to be measured; θ represents the aperture angle of the focusing lens; and n represents the refractive index of the object to be measured.

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