A diffraction correction method for improving the measurement accuracy of a light blocking method particle counter

Abstract

The application discloses a diffraction correction method for improving the measurement accuracy of a light resistance method particle counter. Firstly, according to the standard accuracy of the instrument, the value of the cut-off angle is calculated under the condition of only considering the extinction error of geometric scattering light; then, according to the particle size measurement range of the instrument, the particle size section is divided according to the rule, and the boundary particle size value of each section is obtained; the proportion of the light energy of the diffraction light whose angle is greater than the cut-off angle in the total diffraction light energy generated by the particle of the segmented particle size is calculated, and the apparent particle size section is calculated; finally, if the measured particle size of the particle is in a certain apparent particle size section during the measurement, the particle is counted into the particle size section, wherein the last step is repeatedly performed until the measurement is completed. Then, the measurement report is generated according to the original particle size section, so as to compensate the diffraction error. Compared with the prior art, the method reduces the geometric extinction coefficient error by adjusting the cut-off angle, the increased diffraction error is compensated by numerical calculation, and the measurement precision is significantly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of particle counting technology, and particularly relates to a diffraction correction method capable of improving the measurement accuracy of a light blocking method particle counter. BACKGROUND

[0002] In the prior art, the light blocking method can only measure the light attenuation (extinction) equivalent particle diameter of particles, and cannot measure the true geometric particle diameter of particles. In addition, when measuring particles of the same size, if the optical properties of the particles are different, the instrument will give different particle size results.

[0003] According to the above defects, the current light blocking method particle counter (see reference) is innovated, and the working principle is based on the following physical theory: under the premise that the particle diameter is much larger than the wavelength of light, the scattering of light by the particle can be approximately regarded as the superposition of light diffraction and geometric scattering. For light diffraction, the angular distribution is only related to the particle size, and is independent of the optical properties of the particle. For geometric scattering of light, the angular distribution of far-field scattered light is only related to the optical properties of the particle, and is independent of the particle size. According to this, the optical structure of the current light blocking method particle counter is: a single-color point light source emits a divergent light beam, which becomes parallel light after passing through a lens, and becomes an incident light beam after passing through a beam-limiting diaphragm. The region (flow channel) through which the measured fluid passes is surrounded by the beam-limiting diaphragm, a converging lens, and a support frame, and the flow channel space occupied by the incident light beam is the measurement zone of the instrument, which is located in the center of the flow channel. The pinhole diaphragm is located on the back focal plane of the converging lens, and the detector is located behind the pinhole diaphragm.

[0004] When no particles enter the measurement zone, the incident light is focused at the center of the pinhole diaphragm, and all passes through the pinhole diaphragm to reach the detector. When particles enter the measurement zone, light scattering or absorption occurs, and only the scattered light with an angle smaller than the cutoff angle can be received by the detector. Since the angular distribution range of geometric scattering light is much larger than that of diffraction light, under the condition that the cutoff angle is appropriately selected, the diffraction light can basically pass through the pinhole diaphragm, and the geometric scattering light is basically completely blocked by the pinhole diaphragm, so that the effective extinction coefficient of the particle is approximately 1, and is basically independent of the optical properties of the particle. The light attenuation caused by the particle is equal to the incident light projected onto the particle. Therefore, the instrument can calculate the size of the particle according to the light attenuation and the cross-sectional area of the incident light beam, and the result is not affected by the optical properties and position of the particle.

[0005] However, current optical obscuration particle counters still have some problems. In practical instrument design, the cutoff angle is a trade-off: if the cutoff angle is too large, although more diffracted light passes through the pinhole aperture, more geometrically scattered light will also pass through the pinhole aperture, resulting in an extinction coefficient significantly less than 1; if the cutoff angle is too small, the extinction coefficient of geometric scattering is close to 1, but more diffracted light is blocked, causing errors in particle size calculation (which can be called "diffraction error"). As the measured particles become smaller, the trade-off effect will worsen, and the measurement accuracy of the instrument will also decrease. Summary of the Invention

[0006] In view of this, the present invention discloses a diffraction correction method to improve the measurement accuracy of a photoresist particle counter. This method utilizes a numerical algorithm to correct the measurement results, thereby improving measurement accuracy. The technical solution of the present invention is as follows:

[0007] This invention discloses a diffraction correction method to improve the measurement accuracy of optically resistive particle counters, comprising the following steps:

[0008] S1. Calculate the cutoff angle θ of the optical obscuration particle counter based on the instrument's target accuracy. F The value;

[0009] Specifically, considering only geometric scattering errors, the cutoff angle θ F The calculation process is shown in formula (1) (see references):

[0010]

[0011] In equation (1), σ is the target measurement error and n is the particle refractive index.

[0012] Specifically, σ is a value set manually, and n is the refractive index of the particle with the smallest refractive index that can be measured by the instrument.

[0013] S2. According to the particle size measurement range of the instrument, D0~D M The particles are divided into M size segments according to a certain rule, and the boundary particle size values ​​of each segment are denoted as D0, D1, D2, ..., D... M ;

[0014] Optionally, in step S2, the pattern includes geometric series, arithmetic series, irregular gradation, etc.

[0015] S3. Calculate the particle size as D0, D1, D2, ..., D M The diffraction angle produced by particulate matter is greater than θ F The proportions of the diffracted light energy to the total diffracted light energy are denoted as b0, b1, b2, ..., b... M ;

[0016] Specifically, the b0, b1, b2,..., b M The calculation process is shown in formula (2) (see reference) :

[0017]

[0018] In formula (2), J0 and J1 are 0-order and 1-order Bessel functions respectively, and D is the particle size of the particle.

[0019] S4, respectively calculate the apparent sectional particle size of the particle to be measured with particle sizes of D0, D1, D2,..., D M , and mark them as

[0020] S5, during the measurement, calculate the particle size D of the particle according to the light decay, if D meets , the particle is counted into the i-th particle size section, i = 1, 2,..., M; continue the S5 step until the measurement is completed.

[0021] S6, generate the measurement report of the instrument according to the original particle size sections D0, D1, D2,..., D M .

[0022] Based on the present application, the method can compensate for the measurement error caused by the blocking of part of the diffraction light by the small aperture diaphragm due to the small cutoff angle. The instrument only needs to take the cutoff angle to a low enough value according to the accuracy requirement of the objective, to ensure that the transmission error of the geometric scattering is kept in a small enough range, and the diffraction error caused by the small aperture diaphragm can be compensated by the above method, and finally the goal of improving the measurement accuracy of the light blocking method particle counter is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only one embodiment of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0024] Figure 1 It is a working principle diagram of the light blocking method particle counter.

[0025] In the above drawings, the meanings of the various reference signs are as follows:

[0026] 1, support frame;

[0027] 2, monochromatic point light source;

[0028] 3, collimating lens;

[0029] 4. beam stop;

[0030] 5. measurement area;

[0031] 6. converging lens;

[0032] 7. pinhole stop;

[0033] 8. detector. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments of the present application and the drawings thereof. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the detailed description section of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the use of the terms "including," "comprising," "having" and "with" used in the detailed description and the claims herein are used to mean "including but not limited to.".

[0036] In the description of specific embodiments of the present application, the technical terms "first", "second", and the like are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0037] In the present application, the phrase "embodiments" means that the specific features, structures or properties described in conjunction with the embodiments can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the described embodiments of the present application can be combined with other embodiments.

[0038] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in the present application generally represents an "or" relationship between the associated objects before and after it.

[0039] It should be noted that, for ease of description, all identical technical features are labeled with the same symbols in the following embodiments.

[0040] In existing technologies, the optical obscuration method can only measure the optically attenuated equivalent particle size, and cannot measure the true geometric particle size. Furthermore, when measuring particles of the same size, the instrument will give different particle size results due to differences in the particles' optical properties.

[0041] To address the aforementioned shortcomings, current optically resistive particle counters have been innovated (see references). Their working principle is based on the following physical theory: when the particle size is much larger than the wavelength of light, the scattering of light by the particle can be considered as a superposition of two phenomena: diffraction and geometric scattering. For diffraction, the angular distribution depends only on the particle size and is independent of the particle's optical properties. For geometric scattering, the angular distribution of the far-field scattered light depends only on the particle's optical properties and is independent of the particle size.

[0042] like Figure 1 As shown, in the current operation of the optical obscuration particle counter, the monochromatic point light source 2 emits a diverging beam, which becomes parallel light after passing through the collimating lens 3, and then becomes the incident beam after passing through the beam-limiting aperture 4. The area (flow channel) through which the measured fluid passes is enclosed by the beam-limiting aperture 4, the converging lens 6, and the support frame 1. The flow direction of the fluid is perpendicular to the paper plane. The space occupied by the incident beam in the flow channel is the measurement area 5, which is located in the center of the flow channel. The pinhole aperture 7 is located on the back focal plane of the converging lens 6, and the detector 8 is located behind the pinhole aperture 7.

[0043] When no particles enter the measurement area 5, the incident light is focused at the center of the pinhole aperture 7 and reaches the detector 8 after passing through the pinhole aperture 7. When particles enter the measurement area 5, they cause light scattering or absorption. After passing through the converging lens 6, the scattered light will be converged at the same position on the pinhole aperture 7 with the same scattering angle. The angle subtended by the aperture radius of the pinhole aperture 7 with respect to the optical center of the converging lens 6 is θ. F θ F The size of θ determines the maximum angle of scattered light that can be received by detector 8. That is, only scattered light with an angle smaller than this angle can be received by detector 8; therefore, it is called the "cutoff angle" of the instrument system. F The setup should satisfy two conditions: most of the geometrically scattered light cannot pass through the aperture, while most of the diffracted light can pass through the aperture. Thus, for detector 8, the diffraction of light by the particle has almost no extinction effect, while the geometric scattering of light by the particle has a 100% effect. Therefore, the extinction effect of the particle passing through measurement area 5 comes solely from the particle's absorption (if any) and geometric scattering, with an extinction coefficient approximately 1. The light attenuation is then equal to the incident light intensity multiplied by the particle's geometric cross-sectional area. Based on the ratio of light attenuation to incident light power and the cross-sectional area of ​​the incident beam, the particle diameter can be calculated.

[0044] However, in practical instrument design, the cutoff angle is a compromise: if the cutoff angle is too large, although more diffracted light passes through the aperture 7, more geometrically scattered light also passes through the aperture 7, resulting in an extinction coefficient for geometric scattering that is significantly less than 1. If the cutoff angle is too small, the extinction coefficient for geometric scattering is closer to 1, but more diffracted light is blocked, leading to diffraction errors. As the measured particle becomes smaller, the compromise effect worsens, and the measurement accuracy of the instrument also decreases.

[0045] To address this problem, this invention discloses a diffraction correction method that improves the accuracy of particle counter measurements using optical obscuration. This method utilizes a numerical algorithm to correct the measured particle size, thereby enhancing measurement precision. The steps include the following:

[0046] S1. Based on the instrument's measurement accuracy requirements, calculate the cutoff angle θ of the optical obscuration particle counter under conditions of only geometric scattering error. F The value;

[0047] Specifically, the cutoff angle θ F The calculation is shown in formula (1):

[0048]

[0049] In equation (1), σ is the target measurement error and n is the particle refractive index.

[0050] Specifically, the value of n is the minimum refractive index of the particles that the instrument is to measure.

[0051] S2. According to the particle size measurement range of the instrument, D0~D M According to the pattern, D0~D M Let there be M particle size ranges, and the boundary particle size values ​​of each range be denoted as D0, D1, D2, ..., D... M ;

[0052] Optionally, in step S2, the pattern includes geometric series, arithmetic series, and irregular series.

[0053] S3. Calculate the particle size as D0, D1, D2, ..., D M The diffraction angle produced by the particulate matter to be tested is greater than θ F The proportions of the diffracted light energy to the total diffracted light energy are denoted as b0, b1, b2, ..., b... M ;

[0054] Specifically, the b0, b1, b2, ..., b M The calculation process is shown in formula (2):

[0055]

[0056] In formula (2), J0 and J1 are 0th and 1st Bessel functions respectively.

[0057] S4, calculate the apparent sectional particle size of the to-be-measured particulate matter with particle sizes of D0, D1, D2,..., D M , and mark them as D0, D1, D2,..., D

[0058] S5, measure the particle size of the to-be-measured particulate matter and mark it as D, if D meets , count it into the ith particle size section, i = 1, 2,..., M; continue this step until the measurement is completed.

[0059] S6, the light-blocking particle counter generates a measurement report according to the original particle size sections D0, D1, D2,..., D M .

[0060] Based on the present application, by numerical calculation, the instrument only needs to take the cutoff angle to a sufficiently low value according to the accuracy requirement of the design, to ensure that the transmission error of the geometric scattering is kept within a small range, and the diffraction error caused by the pinhole diaphragm can be compensated by the present method, so as to ultimately achieve the goal of improving the measurement accuracy of the light-blocking particle counter.

[0061] The following is further illustrated by examples:

[0062] Example

[0063] In the present embodiment, a diffraction correction method for improving the measurement accuracy of a light-blocking particle counter is provided, and the specific steps are as follows:

[0064] S1, according to the measurement accuracy of the instrument, calculate the value of the cutoff angle θ F in the light-blocking particle counter;

[0065] Specifically, the calculation of the cutoff angle θ F is shown in formula (1):

[0066]

[0067] In formula (1), σ is the target measurement error, and n is the refractive index of the particles.

[0068] Specifically, n is the value of the smallest refractive index of the particles that can be measured by the instrument.

[0069] In the present embodiment, the value of σ is 0.5%, the value of n is the smallest refractive index of the to-be-measured particulate matter, which is 1.33, and the wavelength of light is 0.650. Since the diffraction error is not considered for the time being, the cutoff angle can be calculated to be 0.050 rad or 2.84° according to formula (1).

[0070] S2, set the particle size measurement range of the instrument to D0~D M ;

[0071] Optionally, in the S2 step, the particle size measurement range of the instrument is 10 μm to 160 μm.

[0072] According to the rule, D0~D M is set to M particle size segments, and the boundary particle size values of each particle size segment are respectively denoted as D0, D1, D2, …, DM. M ;

[0073] Optionally, in the S2 step, the rule adopts a geometric progression.

[0074] In this embodiment, the particle size segments are divided according to a geometric progression, and the coefficient is The segmented particle sizes (original segmented particle sizes) are shown in Table 1.

[0075] S3, calculate the proportion of diffraction light energy whose diffraction angle is greater than θ M generated by particles with particle sizes of D0, D1, D2, …, DM F to the total diffraction light energy, and denote them as b0, b1, b2, …, bM, respectively. M ;

[0076] Specifically, the calculation of b0, b1, b2, …, bM M is shown in formula (2):

[0077]

[0078] In formula (2), J0 and J1 are 0-order and 1-order Bessel functions, respectively.

[0079] In this embodiment, the calculation results of the shielding ratio b are shown in Table 1.

[0080] S4, calculate the apparent segmented particle sizes of the particles to be measured with particle sizes of D0, D1, D2, …, DM M , and denote them as

[0081] In this embodiment, the calculation results of the apparent particle size segments are shown in Table 1.

[0082] S5, measure the particle size of the particles to be measured, and set it to D. If D satisfies , it is counted into the i-th particle size segment, i = 1, 2, …, M;

[0083] Continue the S5 step until the measurement is completed.

[0084] S6, generate a measurement report of the light blocking method particle counter according to the original segmented particle sizes.

[0085] By the above setting, the error caused by the diffraction light which cannot completely pass through the small aperture diaphragm due to too small θ F The principle error of the light blocking method particle counter is only from the error caused by the partial geometric scattering light passing through the small aperture diaphragm. As long as θ F is small enough, the particle size measurement error caused by the partial geometric scattering light received by the detector can be controlled in a small enough range, which is less than 0.5% in the embodiment, which is a very low error (the particle size measurement error allowed by the national standard for the traditional light blocking method instrument is 10%) or a very high accuracy.

[0086] Table 1

[0087]

[0088] In the embodiment, when the light blocking method particle counter calculates a particle size of 20.5 μm, it can be found from Table 1 that the particle belongs to the second particle size section, or the particle size is directly measured as 15.0 μm, so the particle belongs to the first particle size section.

[0089] After the method of the application is modified, the particle size measurement error caused by the diffraction light of the particle being blocked can be completely compensated, and the only principle error source is the geometric scattering light passing through the small aperture diaphragm, and this error can be solved by trying to reduce the cutoff angle, which is 0.5% in the embodiment.

[0090] It should be noted that the above is only a preferred embodiment of the application and does not limit the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

[0091] Reference

[0092] Gong Xin-yu et al., a light blocking method particle counter for measuring real particle size (patent), application number 2025100094134.

Claims

1. A diffraction correction method for improving the measurement accuracy of a light blockage method particle counter, characterized by, The steps include the following: S1. Calculate the numerical value of the cut-off angle of the aperture diaphragm in a light block particle counter, taking into account only the geometrical scattering error, in accordance with the accuracy target of the instrument for particle size measurement from which the instrument determines the aperture radius of the aperture diaphragm; S2. According to the particle size measurement range of the instrument, the particle size measurement range is ; According to the rule, the particle size range of each particle size section is recorded from small to large as is divided into M particle size sections, and the particle size range of each particle size section is recorded from small to large as Here is called a segmented particle size point, and ; S3, the diffraction angle generated by the particles with the particle size of is greater than the cutoff angle The ratio of the diffraction light energy of the numerical value to the total diffraction light energy is respectively recorded as , , ; S4, calculating the apparent sectional particle diameter of the particulate matter to be measured, the apparent sectional particle diameter being , , , , ; S5、In the measuring process, if the particle size D of the particulate measured satisfies: then the particulate is counted into the i-th particle size section, =1,2,...,M; This step is continuously performed until the measurement is stopped; S6, segmenting according to original particle size generating a measurement report; In the S1 step, the cut-off angle is calculated as shown in equation (1): （1） In formula (1), n is the lowest refractive index of the particles measured by the instrument.

2. The diffraction correction method for improving the measurement accuracy of a light blocking method particle counter according to claim 1, characterized in that, In the S2 step, the rule includes equal ratio segmentation, equal difference segmentation, and irregular segmentation.

3. The diffraction correction method for improving the measurement accuracy of a light blocking method particle counter according to claim 1, characterized in that, In the S3 step, the , ,..., calculation is shown in equation (2): （2） In formula (2), are the 0th and 1st order Bessel functions, respectively.

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