Diffraction correction method capable of improving measurement accuracy of photoresist particle counter

Abstract

The invention discloses a diffraction correction method capable of improving the measurement accuracy of a photoresist particle counter, which comprises the following steps of: firstly, calculating the numerical value of a cut-off angle under the condition that only geometric scattered light extinction errors are considered according to the target accuracy of an instrument; according to the particle size measurement range of the instrument, dividing particle size sections according to rules to obtain the boundary particle size value of each section; calculating the proportion of the light energy with the diffraction light angle larger than the cut-off angle generated by the particles with the segmented particle size in the total diffraction light energy, and calculating the apparent particle size segment; and finally, if the measured particle size of the particulate matter is in a certain apparent particle size section during measurement, counting the particle into the diameter section, and repeating the last step until the measurement is finished. And measuring reports are generated according to the original particle size sections so as to compensate for diffraction errors. Compared with the prior art, the method has the advantages that the cut-off angle is lowered, the geometric extinction coefficient error is reduced, the increased diffraction error is compensated through numerical calculation, and the measurement precision is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of particle counting, and in particular to a diffraction correction method capable of improving the measurement accuracy of a particle counter using a light blocking method. Background Art

[0002] In the prior art, the light obstruction method can only measure the particle size equivalent to the light attenuation (extinction) of the particles, but cannot measure the true geometric particle size of the 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] Based on the above defects, the current light-blocking particle counter (see references) has been innovated, and its working principle is based on the following physical theory: Under the premise that the particle size is much larger than the wavelength of light, the scattering of light by particles can be approximately regarded as the superposition of two phenomena: diffraction of light and geometric scattering. For the diffraction of light, its angular distribution is only related to the particle size and has nothing to do with the optical properties of the particles. For the geometric scattering of light, the angular distribution of its far-field scattered light is only related to the optical properties of the particles and has nothing to do with the particle size. Based on this, the optical structure of the current light-blocking particle counter is: a monochromatic 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 aperture. The area (flow channel) through which the measured fluid passes is surrounded by a beam-limiting aperture, a converging lens and a supporting frame. The flow channel space occupied by the incident light beam is the measurement area of ​​the instrument, which is located in the center of the flow channel. The pinhole aperture is located on the back focal plane of the converging lens, and the detector is behind the pinhole aperture.

[0004] When no particles enter the measurement area, the incident light is focused at the center of the pinhole aperture and all passes through the pinhole aperture to reach the detector. When particles enter the measurement area, light scattering or absorption occurs, and only the part of the scattered light with an angle less than the cutoff angle can be received by the detector. Since the distribution angle range of the geometric scattered light is much larger than the distribution angle range of the diffracted light, when the cutoff angle is taken appropriately, the diffracted light can basically all pass through the pinhole aperture, while the geometric scattered light is basically completely blocked by the pinhole aperture. Therefore, the effective extinction coefficient of the particle is approximately 1 and has little to do with 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 based on 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, the current light-blocking particle counter still has some problems. In actual instrument design, the cutoff angle is a compromise: if the cutoff angle is too large, although more diffracted light passes through the pinhole aperture, more geometric 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, resulting in a calculated error in the particle size (which can be called a "diffraction error"). As the measured particles become smaller, the compromise effect will become worse, 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 that can improve the measurement accuracy of a light-blocking particle counter, and uses a numerical algorithm to correct the measurement result to improve the measurement accuracy. The technical solution of the present invention is as follows:

[0007] The present invention discloses a diffraction correction method for improving the measurement accuracy of a light-blocking particle counter, comprising the following steps:

[0008] S1. Calculate the cutoff angle θ of the light-blocking particle counter according to the target accuracy of the instrument. F The value of

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

[0010]

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

[0012] Specifically, σ is an artificially set value, and n is the refractive index value 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 , it is divided into M particle size segments according to a certain rule, and the boundary particle size values ​​of each particle size segment are recorded as D0, D1, D2, ..., D M ;

[0014] Optionally, in step S2, the rules include geometric progression, arithmetic progression, irregular grading, etc.

[0015] S3, calculate the particle size as D0, D1, D2, ..., D M The diffraction angle of particles is greater than θ F The proportion of the diffracted light energy to the total diffracted light energy is recorded as b0, b1, b2, ..., b M ;

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

[0017]

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

[0019] S4, calculate the particle sizes D0, D1, D2, ..., D M The apparent segmented particle sizes of the particles to be tested are recorded as

[0020] S5. During the measurement process, the particle size D is calculated based on the light attenuation. If D satisfies The particle is then counted into the i-th particle size segment, i=1, 2, ..., M; and step S5 is continued until the measurement is completed.

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

[0022] Based on the invention, this method can compensate for the measurement error caused by the blocking of part of the diffracted light by the pinhole aperture due to the cutoff angle being too small through numerical calculation. The instrument only needs to set the cutoff angle to a sufficiently low value according to the target accuracy requirements to ensure that the transmission error of geometric scattering is kept within a sufficiently small range, while the diffraction error caused by the pinhole aperture blocking can be compensated by the above method, ultimately achieving the goal of improving the measurement accuracy of the light-blocking particle counter. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is the working principle diagram of the light obstruction particle counter.

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

[0026] 1. Support frame;

[0027] 2. Monochromatic point light source;

[0028] 3. Collimating lens;

[0029] 4. Beam limiting aperture;

[0030] 5. Measurement area;

[0031] 6. Converging lens;

[0032] 7. Pinhole diaphragm;

[0033] 8. Detector. DETAILED DESCRIPTION

[0034] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0036] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. 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 invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0037] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0038] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

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

[0040] In the prior art, the existing light obstruction method can only measure the light attenuation equivalent particle size of particles, but cannot measure the true geometric particle size of particles. In addition, when measuring particles of the same size, the instrument will give different particle size results due to the different optical properties of the particles.

[0041] Based on the above defects, the current light-blocking particle counter has been innovated (see references). Its working principle is based on the following physical theory: Under the premise that the particle size is much larger than the wavelength of light, the scattering of light by particles can be regarded as the superposition of two phenomena: diffraction and geometric scattering of light. For the diffraction of light, its angular distribution is only related to the particle size and has nothing to do with the optical properties of the particles. For the geometric scattering of light, the angular distribution of the far-field scattered light is only related to the optical properties of the particles and has nothing to do with the particle size.

[0042] like Figure 1 As shown, in the working process of the current light blocking particle counter, the monochromatic point light source 2 emits a divergent light beam, which becomes parallel light after passing through the collimating lens 3, and becomes an incident light beam after passing through the beam limiting aperture 4; the area (flow channel) through which the measured fluid passes is surrounded by the beam limiting aperture 4, the converging lens 6 and the support frame 1, and the flow direction of the fluid is perpendicular to the paper surface. The space occupied by the incident light beam in the flow channel is the measuring 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 through the pinhole aperture 7. After the particles enter the measurement area 5, light scattering or absorption will occur. After the scattered light passes through the converging lens 6, the same scattering angle will be converged to the same position of the pinhole aperture 7. The opening angle of the aperture radius of the pinhole aperture 7 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 the detector 8, that is, only scattered light with an angle smaller than this angle can be received by the detector 8, so it is called the "cut-off angle" of the instrument system. F The setting should satisfy the two conditions that most of the geometric scattered light cannot pass through the small hole, while most of the diffracted light can pass through the small hole. In this way, for the detector 8, the diffraction phenomenon of the particles on the light has almost no extinction effect, while the geometric scattering of the particles on the light plays a 100% role, so the extinction effect of the particles passing through the measurement area 5 comes from the absorption (if any) and geometric scattering of the particles, and the extinction coefficient is approximately 1. In this way, the light attenuation is equal to the incident light intensity multiplied by the geometric cross-sectional area of ​​the particle. According to the ratio of the light attenuation to the incident light power and the cross-sectional area of ​​the incident light beam, the particle diameter can be calculated.

[0044] However, in actual instrument design, the cutoff angle is a compromise: if the cutoff angle is too large, although more diffracted light passes through the pinhole aperture 7, more geometric scattered light also passes through the aperture 7, resulting in the extinction coefficient of geometric scattering being significantly less than 1. If the cutoff angle is too small, the extinction coefficient of geometric scattering is closer to 1, but more diffracted light is blocked, resulting in diffraction errors. As the measured particles become smaller, the compromise effect will become worse, and the measurement accuracy of the instrument will also decrease.

[0045] To solve this problem, the present invention discloses a diffraction correction method that can improve the measurement accuracy of a light-blocking particle counter, which uses a numerical algorithm to correct the measured particle size result to achieve the purpose of improving the measurement accuracy, including the following steps:

[0046] S1. According to the measurement accuracy requirements of the instrument, calculate the cutoff angle θ of the light blocking particle counter under the condition of only geometric scattering error. F The value of

[0047] Specifically, the cut-off angle θ F The calculation of is shown in formula (1):

[0048]

[0049] In formula (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 particles that the instrument is intended to measure.

[0051] S2, according to the particle size measurement range of the instrument D0~D M , according to the rule, D0~D M Assume that there are M particle size segments, and the boundary particle size values ​​of each particle size segment are recorded as D0, D1, D2, ..., D M ;

[0052] Optionally, in step S2, the rules include 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 particles to be measured is greater than θ F The proportion of the diffracted light energy to the total diffracted light energy is recorded as b0, b1, b2, ..., b M ;

[0054] Specifically, 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 order Bessel functions respectively.

[0057] S4, calculate the particle size D0, D1, D2, ..., D M The apparent segmented particle sizes of the particles to be tested are recorded as

[0058] S5. Measure the particle size of the particle to be tested and record it as D. If D satisfies Then it is counted into the i-th particle size segment, i = 1, 2, ..., M; continue this step until the measurement is completed.

[0059] S6, light obstruction particle counter is divided into segments D0, D1, D2, ..., D M Generate measurement reports.

[0060] Based on the invention, this method uses numerical calculations, and the instrument only needs to set the cutoff angle to a sufficiently low value according to the accuracy requirements of the design to ensure that the transmission error of the geometric scattering remains within a small range. The diffraction error caused by the obstruction of the small aperture can be compensated by this method, ultimately achieving the goal of improving the measurement accuracy of the light obstruction method particle counter.

[0061] The following is further described by examples:

[0062] Example

[0063] In this 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. Calculate the cutoff angle θ in the light obstruction particle counter according to the target accuracy of the instrument. F The value of

[0065] Specifically, the cut-off angle θ F The calculation of is shown in formula (1):

[0066]

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

[0068] Specifically, n is the value of the smallest refractive index in a particle that the instrument can possibly measure.

[0069] In this embodiment, the value of σ is 0.5%, n is the minimum refractive index of the measured particles, which is 1.33, and the wavelength of light is 0.650. Since the diffraction error is not considered for the time being, the cut-off angle can be calculated by formula (1) to be 0.050 rad or 2.84°.

[0070] S2. Assume that the particle size measurement range of the instrument is D0~D M ;

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

[0072] According to the rule, D0~D M Assume that there are M particle size segments, and the boundary particle size values ​​of each particle size segment are recorded as D0, D1, D2, ..., D M ;

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

[0074] In this embodiment, the particle size segments are divided into grades according to the geometric law, and the coefficient is The segmented particle size (original segmented particle size) is shown in Appendix 1.

[0075] S3, calculate the particle size as D0, D1, D2, ..., D M The diffraction angle of particles is greater than θ F The proportion of the diffracted light energy to the total diffracted light energy is recorded as b0, b1, b2, ..., b M ;

[0076] Specifically, b0, b1, b2, ..., b M The calculation of is shown in formula (2):

[0077]

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

[0079] In this embodiment, the calculation result of the occlusion ratio b is shown in Appendix 1.

[0080] S4, calculate the particle size D0, D1, D2, ..., D M The apparent segmented particle sizes of the particles to be tested are recorded as

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

[0082] S5. Measure the particle size of the particle to be measured and set it as D. If D satisfies Then it is included in the i-th particle size segment, i = 1, 2, ..., M;

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

[0084] S6. Generate a measurement report of the light obstruction particle counter according to the original segmented particle size.

[0085] Through the above settings, the F The error caused by the diffracted light not being able to completely pass through the small aperture diaphragm is so great that the principle error of the light blocking particle counter only comes from the error caused by part of the geometric scattered light passing through the small aperture diaphragm. F Small enough, the particle size measurement error caused by the geometric scattered light part being received by the detector can be controlled within a sufficiently small range. In the present embodiment, it is less than 0.5%, which is an extremely low error for the light obscuration method instrument (for the traditional light obscuration method instrument, the particle size measurement error allowed by the national standard is 10%), or an extremely high accuracy.

[0086] Schedule 1

[0087]

[0088] In this embodiment, when the light obstruction particle counter calculates a particle size of 20.5 μm, it can be found from Appendix 1 that the particle belongs to the second particle size segment, or when the particle size is directly measured to be 15.0 μm, the particle belongs to the first particle size segment.

[0089] After correction using the method of the present application, the particle size measurement error caused by the obstruction of the diffraction light of the particles can be completely compensated. The only fundamental source of error is the geometric scattered light passing through the small hole aperture, and this error can be solved by minimizing the cutoff angle. In the present embodiment, this error is 0.5%.

[0090] It should be pointed out that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0091] References

[0092] Gong Xinyu et al., A light obstruction particle counter for measuring true particle size (patent), application number 2025100094134.

Claims

1. A diffraction correction method for improving the measurement accuracy of a light-blocking particle counter, characterized in that: The steps include: S1. According to the particle size measurement accuracy target of the instrument, the cutoff angle θ of the aperture diaphragm in the light blocking particle counter is calculated under the condition of considering only the geometric scattering error. F The value of , the instrument determines the aperture radius of the pinhole diaphragm based on this; S2, according to the particle size measurement range of the instrument, recorded as D0~D M ; According to the rule, D0~D M It is divided into M particle size segments, and the boundary particle size values ​​of each particle size segment are recorded as D0, D1, D2, ..., D M S3, calculate the particle size as D0, D1, D2, ..., D M The diffraction angle of particles is greater than θ F The proportion of the diffracted light energy to the total diffracted light energy is recorded as b0, b1, b2, ..., b M ; S4, calculate the particle size D0, D1, D2, ..., D M The apparent segmented particle sizes of the particles to be tested are recorded as S5. During the measurement process, if the particle size D of the measured particles satisfies: Then the particle is counted into the i-th particle size segment, i = 1, 2, ..., M; Continue this step until the measurement stops; S6, according to the original particle size segmentation D0, D1, D2, ..., D M Generate measurement reports.

2. A diffraction correction method for improving the measurement accuracy of a light-blocking particle counter according to claim 1, characterized in that: In step S1, the cut-off angle θ F The calculation process is shown in formula (1): In formula (1), σ is the target measurement error, and n is the lowest refractive index of the particles measured by the instrument.

3. A diffraction correction method for improving the measurement accuracy of a light-blocking particle counter according to claim 1, characterized in that: In step S3, the rules include equal segmentation, equal difference segmentation and irregular segmentation.

4. A diffraction correction method for improving the measurement accuracy of a light-blocking particle counter according to claim 1, characterized in that: In step S3, b0, b1, b2, ..., b M The calculation of is shown in formula (2): In formula (2), J0 and J1 are 0th and 1st order Bessel functions respectively.

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