Grinding liquid film thickness measuring device and measuring method thereof

Abstract

The application provides a grinding liquid film thickness measuring device and a measuring method thereof and relates to the technical field of semiconductor processing processes. The light emitted by the light source forms first light and second light through the setting of the measuring assembly. Since the grinding liquid serves as a medium between the second light, the thickness of the grinding liquid can be obtained in real time by measuring the optical path difference change between the first light and the second light through the principle of the Michelson interferometer.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor processing technology, and in particular to a grinding liquid film thickness measuring device and a measuring method thereof. Background Art

[0002] The epitaxial growth process is crucial for semiconductor device fabrication. Sapphire is a widely used semiconductor substrate material due to its excellent chemical stability, high dielectric constant, high thermal conductivity, and relatively low price. Qualified sapphire substrates undergo a complex and precise processing process, including wire sawing, grinding, and polishing. Double-sided grinding, which resists pressure and achieves rapid substrate thinning while improving surface flatness and surface accuracy, is a key step in substrate fabrication.

[0003] The "water film effect" is a key factor affecting the efficiency and quality of double-sided grinding of large-scale sapphire substrates. While the grinding fluid plays a key role in cooling, lubricating, and removing chips during double-sided grinding of substrates, in high-speed, closed processing environments, the "water film effect" can be a significant factor in inducing substrate "processing accidents" and reducing grinding efficiency. The "water film effect" can lead to the following problems during substrate grinding: ① Excessive water film resistance results in insufficient contact between the abrasive and the substrate, resulting in ineffective processing. ② Uneven distribution of water film resistance causes the machining surfaces of the grinding disc and the substrate to be inclined, affecting the surface flatness of the workpiece. ③ Increasing grinding pressure to offset water film resistance can lead to an increase in substrate fragmentation. Furthermore, the larger the sapphire substrate, the more pronounced these problems become.

[0004] Therefore, overcoming the "water film effect" is the key to overcoming the precision issues in manufacturing large-scale sapphire substrates. To overcome this problem, the thickness of the grinding fluid film must first be measured. This thickness can serve as a key indicator for adjusting the cutting force and angle of the abrasive tool. However, existing measurement methods make it difficult to measure the thickness of the grinding fluid film in real time during substrate fabrication. This is because the gap between the abrasive tool and the substrate is extremely small, and they are in high-speed relative rotation. Therefore, it is impossible to insert sensors or measuring tools into the grinding fluid film.

[0005] The existing patent number "CN114719764A" provides a bubble liquid film thickness testing device based on a laser interference system, which belongs to the field of bubble liquid film thickness testing technology, including a digital interferometer, the digital interferometer including a laser transmitter, a first stainless steel support rod group, a second stainless steel support rod group, a cage cube, a lens extension tube, an industrial camera, an aluminum film reflector, an aluminum film mirror frame, an aluminum film mirror frame fine-tuning nut, a breadboard, a fixed mounting frame and a stainless steel column. The present invention can automatically test the bubble liquid film thickness through the laser interference method, and can directly display the bubble interference fringes on the computer display screen. The bubble liquid film thickness and elastic coefficient can be calculated by the change in the interference fringes spacing. It has a simple structure and is highly practical. However, its measurement object is very single, and it can only measure the bubble thickness under relatively ideal conditions, and can only meet static measurement requirements, and cannot achieve dynamic measurement, nor can it achieve real-time measurement during substrate processing. Summary of the Invention

[0006] The invention discloses a device for measuring the thickness of a grinding liquid film, aiming to improve the problem that the thickness of the cutting fluid of existing semiconductor equipment cannot be measured.

[0007] The present invention adopts the following scheme:

[0008] The present application provides a grinding liquid film thickness measuring device, which is suitable for measuring the thickness of a grinding liquid film between a diamond grinding disc and a light-transmitting substrate, comprising: a measuring assembly, wherein the bottom surface of the diamond grinding disc comprises a plurality of micro grooves arranged in a straight line and at equal intervals, wherein a reflective lens is provided in the micro groove to form a second laser reflector;

[0009] The measuring assembly includes a light source emitter having a first optical tube and a second optical tube, and a beam splitter disposed between the first optical tube and the diamond grinding wheel, a compensation plate being further disposed between the beam splitter and the diamond grinding wheel, wherein a first laser reflector and a light detector are respectively disposed on opposite sides of the beam splitter;

[0010] The first optical tube is provided with a plurality of emitting devices corresponding to the micro grooves on the diamond grinding disc to emit the light emitted by the light source to the second laser reflecting mirror, and receive the light reflected from the second laser reflecting mirror, and can pass through the second optical tube and be reflected again by the second laser reflecting mirror to the light detector;

[0011] The laser line emitted from the emitting device is suitable for passing through the beam splitter and the compensation plate to irradiate the second laser reflector, and at the same time, the beam splitter is suitable for reflecting part of the light to the first laser reflector, and the first laser reflector is suitable for reflecting the light back to the beam splitter. The light reflected back by the first laser reflector passes through the beam splitter and the second optical path tube again to be received by the light detector; there is an optical path difference between the light reflected back from the second laser reflector and the light reflected back from the first laser reflector, and the light detector is suitable for obtaining the change in the optical path difference to obtain the thickness of the grinding fluid film.

[0012] Furthermore, the first laser reflecting mirror and the second laser reflecting mirror are perpendicular to each other.

[0013] Furthermore, the beam splitter plate and the compensation plate are parallel to each other.

[0014] Furthermore, the light detector is connected to a computer processing system to calculate the change in the optical path difference between the acquired light rays.

[0015] Furthermore, the micro grooves are square grooves.

[0016] Furthermore, the plane where the diamond grinding disc is located is perpendicular to the central axis of the first optical tube, and the axis of the light detector is perpendicular to the axis of the diamond grinding disc and coincides with the axis of the second optical tube.

[0017] The present invention also provides a method for measuring the thickness of a grinding liquid film, which comprises the following steps using any one of the above-mentioned grinding liquid film thickness measuring devices:

[0018] S1. During the processing, a light source emits monochromatic light, which is directed parallel to a beam splitter. A portion of the light is reflected by the beam splitter to a first laser reflector, which is then reflected by the first laser reflector and then passes through the beam splitter to be received by the light detector. This portion is defined as the first light. Another portion of the light passes through the beam splitter and the compensation plate, then propagates toward the second laser reflector. After being reflected by the second laser reflector, it passes through the compensation plate and then also propagates toward the light detector and is received by the light detector. This portion of the light is defined as the second light. The first and second light rays are coherent light. The compensation plate is adapted to allow both the first and second light rays to pass through a flat glass of equal thickness three times to avoid an additional optical path difference between the first and second light rays.

[0019] S2. The wavelength of the incident monochromatic light is defined as λ, based on the equally spaced interference fringes observed by the light detector. Each time the first laser reflector moves forward or backward by a distance of λ / 2, the interference fringes shift by one, and the number of fringes shifted in the field of view is measured as Δn. The distance the first laser reflector moves is:

[0020]

[0021] The optical path difference is:

[0022] Δ = 2d, where d is the spacing between micro grooves;

[0023] When there is grinding fluid between the second laser reflector and the compensation plate, the optical path difference becomes:

[0024] Δ'=2d+2(n-1)t;

[0025] The change in optical path difference is:

[0026] Δ'-Δ=2(n-1)t, where t is the measured thickness of the grinding fluid;

[0027] The number of shifts of the interference fringes is:

[0028] 2(n-1)t=Δkλ;

[0029] The measured thickness of the grinding fluid medium is obtained as:

[0030]

[0031] This thickness includes the depth of the micro grooves in the diamond grinding wheel, so we need to remove twice the depth of the micro grooves to obtain the final grinding fluid medium thickness:

[0032]

[0033] Furthermore, after the measurement component is installed, the light source emits laser pulses higher than 10000 Hz through the first optical path tube to calibrate the relative position of the second laser reflector and the first optical path tube on the grinding wheel; when the rotation speed of the diamond grinding wheel is stable, the moment when the second laser reflector is aligned with the first optical path tube is selected as the moment to start measurement.

[0034] Beneficial effects:

[0035] Taking advantage of the high light transmittance of transparent substrates, such as large-scale sapphire substrates, the thickness of the grinding fluid film is measured using light refraction. The measurement assembly is configured so that the light emitted by the light source forms a first light beam and a second light beam. Because the grinding fluid acts as a medium between the second light beam, the change in the optical path difference between the first and second light beams can be used to determine the thickness of the grinding fluid. This thickness can be measured in real time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 1 is a schematic structural diagram of a device for measuring the thickness of a grinding liquid film according to an embodiment of the present invention;

[0037] Figure 2 This is a schematic diagram of the principle of a Michelson interferometer formed by a device for measuring the thickness of a grinding liquid film according to an embodiment of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of a grinding liquid film thickness measuring device during measurement of grinding liquid according to an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of the internal structure of a measuring component of a device for measuring the thickness of a grinding liquid film according to an embodiment of the present invention;

[0040] Figure 5 Schematic diagram of the structure of micro grooves on a diamond grinding tool of a device for measuring the thickness of a grinding liquid film according to an embodiment of the present invention;

[0041] Icons: diamond grinding wheel 1, grinding fluid film 2, transparent substrate 3, emitting device 4, first optical path tube 5, second optical path tube 6, measuring component 7, electrical interface 8, light detector 9, light beam collector 10, communication interface 11, compensation plate 12, first laser reflector 13, beam splitter 14, light source emitter 15, micro groove 16, second laser reflector 17, virtual image 18. DETAILED DESCRIPTION

[0042] Example 1

[0043] Combine Figures 1 to 5 As shown, this embodiment provides a grinding liquid film thickness measuring device, which is suitable for measuring the thickness of a grinding liquid film 2 between a diamond grinding disc 1 and a light-transmitting substrate, comprising: a measuring component 7, wherein the bottom surface of the diamond grinding disc 1 includes a plurality of micro grooves 16 arranged in a straight line and at equal intervals, and a reflective lens is provided in the micro grooves 16 to form a second laser reflector 17;

[0044] The measuring assembly 7 includes a light source emitter 15 having a first optical tube 5 and a second optical tube 6, and a beam splitter 14 disposed between the first optical tube 5 and the diamond grinding wheel 1. A compensation plate 12 is further disposed between the beam splitter 14 and the diamond grinding wheel 1. A first laser reflector 13 and a light detector 9 are respectively disposed on opposite sides of the beam splitter 14.

[0045] The first optical tube 5 is provided with a plurality of emitting devices 4 corresponding to the micro grooves 16 on the diamond grinding disc 1 to emit the light emitted by the light source to the second laser reflector 17, and receive the light reflected from the second laser reflector 17, and can pass through the second optical tube 6 and be reflected again by the second laser reflector 17 to the light detector 9;

[0046] The laser line emitted from the emitting device 4 is suitable for passing through the beam splitter 14 and the compensation plate 12 to irradiate the second laser reflector 17. At the same time, the beam splitter 14 is suitable for reflecting part of the light to the first laser reflector 13. The first laser reflector 13 is suitable for reflecting the light back to the beam splitter 14. The light reflected back by the first laser reflector 13 passes through the beam splitter 14 and the second optical path tube 6 again to be received by the light detector 9. There is an optical path difference between the light reflected back from the second laser reflector 17 and the light reflected back from the first laser reflector 13. The light detector 9 is suitable for obtaining the change in the optical path difference to obtain the thickness of the grinding fluid film 2.

[0047] Combine Figures 1 to 4 As shown, in this embodiment, the beam splitter 14 and the compensation plate 12 are both flat glass transparent plates and have the function of reflecting light. The beam splitter 14 and the compensation plate 12 are arranged obliquely and tend to be parallel to each other.

[0048] Combine Figures 1 to 5 As shown, the diamond grinding tool has square micro grooves 16 arranged in a straight line and at equal intervals along the diameter direction on its surface while maintaining its original performance. The number of micro grooves 16 is several, the length is defined as a, the interval between adjacent micro grooves 16 is defined as d, and the depth of the micro grooves 16 is defined as h. A reflective lens is installed at the bottom of the groove, and the size of the lens is almost the same as the size of the groove. The multiple micro grooves 16 and the reflective lens constitute the second laser reflector 17. The grooves are opened and the lenses are installed on the diamond grinding tool in order to combine with the emitting device 4 on the first optical path tube 5. When the emitting device 4 of the first optical path tube 5 emits a laser to the diamond grinding tool, the reflective lens in the micro groove 16 can reflect the laser back, thus forming a reflector in the Michael interferometer.

[0049] Combine Figure 4 As shown, the light source emitter 15 of the measuring assembly 7 is equipped with a light beam collector 10 and mutually perpendicular first and second optical tubes 5 and 6. The light beam collector 10 is used to receive the first and second light beams. The plane of the diamond grinding wheel 1 is perpendicular to the central axis of the first optical tube 5. The axis of the light detector 9 is perpendicular to the axis of the diamond grinding wheel 1 and coincides with the axis of the second optical tube 6. A plurality of emitting devices 4 are disposed above the first optical tube 5, corresponding to the micro-grooves 16 on the diamond grinding wheel 1. These emitters 4 transmit light emitted by the light source to the second laser reflector 17 and receive light reflected from the second laser reflector 17. The number of emitting devices 4 is the same as the number of micro-grooves 16, and they correspond one-to-one. Their function is to divert the laser light passing through the first optical tube 5, guiding the light upward through the multiple emitting devices 4 so that the laser light can be emitted to the second laser reflector 17 in the micro-grooves 16 of the diamond grinding wheel and reflected back. The reflected light is then received again and transmitted to the measuring assembly 7. This can form Figure 2 The reflection process from the compensation plate 12 to the second laser reflection plate in the Michael interferometer principle shown in FIG.

[0050] In this embodiment, the transparent substrate 3 can be a large-sized sapphire substrate. The light detector 9 is connected to a computer processing system via a communication interface 11 to calculate the change in the optical path difference between the acquired light rays. The computer processing system can be connected to a display. The number of interference fringes between the first light ray and the second light ray can be automatically analyzed in real time by the computer system. The computer software can accurately and quickly output the thickness of the grinding fluid in real time, thereby obtaining accurate dynamic data. The computer system can directly output an image through the display, and the change in the thickness of the grinding fluid can be intuitively counted through the image to analyze the thickness change pattern of the grinding fluid during the grinding process. The light source emitter 15 is provided with an electrical interface 8, which can adjust the laser type and pulse frequency for measuring materials of different colors and transmittances.

[0051] Combine Figures 2 to 4As shown, during the processing, the light source emits monochromatic light, which is directed parallel to the beam splitter 14. A portion of the light is reflected by the beam splitter 14 to the first laser reflector 13, and after being reflected by the first laser reflector 13, it passes through the beam splitter 14 and is received by the light detector 9, which is defined as the first light; another portion of the light passes through the beam splitter 14 and the compensation plate 12, and after passing through the compensation plate 12, it propagates to the second laser reflector 17, and after being reflected by the second laser reflector 17, it passes through the compensation plate 12 and is reflected by the beam splitter 14 and is also propagated to the light detector 9, and is received by the light detector 9, which is defined as the second light; the first light and the second light are coherent light, and the compensation plate 12 is suitable for allowing the first light and the second light to pass through the flat glass of the same thickness three times to avoid additional optical path difference between the first light and the second light.

[0052] The light detector 9 can be used to observe interference fringes of equal spacing on the computer system. The wavelength of the incident monochromatic light is defined as λ. Then, whenever the first laser reflector 13 moves forward or backward by a distance of λ / 2, the interference fringes shift by one, and the number of fringes shifted in the field of view is measured as Δn. The distance moved by the first laser reflector 13 is:

[0053]

[0054] The optical path difference is:

[0055] Δ=2d, where d is the distance between the micro grooves 16 . In this case, there is no other medium between the second laser reflecting mirror 17 and the compensation plate 12 .

[0056] When there is grinding fluid between the second laser reflection mirror 17 and the compensation plate 12, the optical path difference becomes:

[0057] Δ'=2d+2(n-1)t

[0058] ;Wherein, t is the measured thickness of the grinding fluid;

[0059] The change in optical path difference is:

[0060] Δ'-Δ=2(n-1)t;

[0061] The number of shifts of the interference fringes is:

[0062] 2(n-1)t=Δkλ;

[0063] The measured thickness of the grinding fluid medium is obtained as:

[0064]

[0065] Since the measured thickness includes the depth of the grooves in the grinding disc, we need to remove twice the depth of the grooves to obtain the final grinding fluid medium thickness:

[0066]

[0067] The device of this embodiment can dynamically and in real time measure the thickness of the grinding fluid film during the grinding process. It should be noted that the device of this embodiment is not only applicable to the processing of large-scale sapphire substrates, but also applicable to the measurement of various transparent / translucent materials during processing.

[0068] Example 2

[0069] Combine Figures 1 to 4 As shown, the present invention also provides a method for measuring the thickness of a grinding liquid film, which comprises the following steps using the above-mentioned grinding liquid film thickness measuring device:

[0070] S1. During the processing, the light source emits monochromatic light, which is directed parallel to the beam splitter 14. A portion of the light is reflected by the beam splitter 14 to the first laser reflector 13, and then passes through the beam splitter 14 after being reflected by the first laser reflector 13 and is received by the light detector 9. This is defined as the first light. Another portion of the light passes through the beam splitter 14 and the compensation plate 12, and then propagates to the second laser reflector 17 after passing through the compensation plate 12. After being reflected by the second laser reflector 17, it passes through the compensation plate 12 and is reflected by the beam splitter 14 and is also propagated to the light detector 9 and is received by the light detector 9. This is defined as the second light. The first and second lights are coherent lights. The compensation plate 12 is suitable for allowing the first and second lights to pass through the flat glass of the same thickness three times to avoid an additional optical path difference between the first and second lights.

[0071] S2, the light reflected by the second laser reflector 17 will form a virtual image 18 behind the first laser reflector 13 after passing through the beam splitter 14. Therefore, the light reflected from the second laser reflector 17 can be regarded as emanating from the virtual image 18. In this way, the optical path difference between the first and second coherent light rays is mainly determined by the distance from the beam splitter 14 to the first laser reflector 13 and the virtual image 18. Usually, the first laser reflector 13 and the second laser reflector 17 are not strictly perpendicular, so the virtual image 18 and the first laser reflector 13 are not strictly parallel, and the thin layer of air between them forms an air wedge; at this time, the interference fringes observed are equally spaced and equal-thickness fringes; therefore, the wavelength of the incident monochromatic light is defined as λ, and whenever the first laser reflector 13 moves forward or backward by a distance of λ / 2, the interference fringes are translated by one, and the number of fringes that have moved in the field of view is measured as Δn. The distance moved by the first laser reflector 13 is:

[0072]

[0073] The optical path difference is:

[0074] Δ=2d, where d is the spacing between the micro grooves 16;

[0075] When there is grinding fluid between the second laser reflection mirror 17 and the compensation plate 12, the optical path difference becomes:

[0076] Δ'=2d+2(n-1)t

[0077] , where t is the measured thickness of the grinding fluid;

[0078] The change in optical path difference is:

[0079] Δ'-Δ=2(n-1)t;

[0080] The number of shifts of the interference fringes is:

[0081] 2(n-1)t=Δkλ;

[0082] The measured thickness of the grinding fluid medium is obtained as:

[0083]

[0084] The measured thickness includes the depth of the micro grooves in the diamond grinding wheel 1, so twice the depth of the micro grooves should be removed to obtain the final grinding fluid medium thickness:

[0085]

[0086] In this embodiment, after the measuring component 7 is installed, the light source emitter 15 emits laser pulses higher than 10000 Hz through the first optical path tube 5 to calibrate the relative position of the second laser reflector 17 on the grinding wheel and the first optical path tube 5; when the rotation speed of the diamond grinding wheel 1 is stable, the moment when the second laser reflector 17 is aligned with the first optical path tube 5 is selected as the moment to start measurement.

[0087] It should be noted that, since the thickness of the liquid film during the grinding process needs to be measured dynamically and in real time, it is necessary to consider whether the frequency of the laser pulse matches the frequency of the second laser reflector 17 on the diamond grinding disc 1 aligning with the emission device 4 of the first optical path tube 5 during the rotation of the diamond grinding disc 1. During calibration, after the rotation speed of the diamond grinding disc 1 stabilizes, the rotation speed of the diamond grinding disc 1 is set to v and the frequency of the laser pulse is set to f. Since the reflective lenses are evenly arranged according to the diameter on the diamond grinding disc 1, the reflective lenses and the emission device 4 will align twice for each rotation of the diamond grinding disc 1. Therefore, the frequency of the laser pulse at this time is:

[0088] In this embodiment, when a medium is inserted between the second laser reflector 17 and the compensation plate 12, the optical path difference changes, so that the thickness of the medium can be measured. The medium here is grinding fluid, which is between the second laser reflector 17 and the compensation plate 12.

[0089] Through the solution of this embodiment, the thickness of the grinding liquid film can be dynamically measured in real time when the transparent substrate 3 is being manufactured.

[0090] It should be understood that the above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

[0091] The above description of the drawings used in the implementation manner only shows certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without making any creative efforts.

Claims

1. A grinding liquid film thickness measuring device, which is suitable for measuring the thickness of the grinding liquid film between a diamond grinding disc and a light-transmitting substrate, characterized in that: include: The measuring component comprises a bottom surface of the diamond grinding disc including a plurality of micro grooves arranged in a straight line and at equal intervals, wherein a reflective lens is provided in the micro groove to form a second laser reflector; The measuring assembly includes a light source emitter having a first optical tube and a second optical tube, and a beam splitter disposed between the first optical tube and the diamond grinding wheel, a compensation plate being further disposed between the beam splitter and the diamond grinding wheel, wherein a first laser reflector and a light detector are respectively disposed on opposite sides of the beam splitter; The first optical tube is provided with a plurality of emitting devices corresponding to the micro grooves on the diamond grinding disc to emit the light emitted by the light source to the second laser reflecting mirror, and receive the light reflected from the second laser reflecting mirror, and can pass through the second optical tube and be reflected again by the second laser reflecting mirror to the light detector; The laser line emitted from the emitting device is suitable for passing through the beam splitter and the compensation plate to irradiate the second laser reflector, and at the same time, the beam splitter is suitable for reflecting part of the light to the first laser reflector, and the first laser reflector is suitable for reflecting the light back to the beam splitter. The light reflected back by the first laser reflector passes through the beam splitter and the second optical path tube again to be received by the light detector; there is an optical path difference between the light reflected back from the second laser reflector and the light reflected back from the first laser reflector, and the light detector is suitable for obtaining the change in the optical path difference to obtain the thickness of the grinding fluid film.

2. The grinding liquid film thickness measuring device according to claim 1, characterized in that: The first laser reflecting mirror and the second laser reflecting mirror are perpendicular to each other.

3. The grinding liquid film thickness measuring device according to claim 2, characterized in that: The beam splitter plate and the compensation plate are parallel to each other.

4. The grinding liquid film thickness measuring device according to claim 1, characterized in that: The light detector is connected to a computer processing system to calculate the change of the optical path difference between the acquired light rays.

5. The grinding liquid film thickness measuring device according to claim 1, characterized in that: The micro grooves are square grooves.

6. The grinding liquid film thickness measuring device according to claim 1, characterized in that: The plane where the diamond grinding disc is located is perpendicular to the central axis of the first optical tube, and the axis of the light detector is perpendicular to the axis of the diamond grinding disc and coincides with the axis of the second optical tube.

7. A method for measuring the thickness of a grinding liquid film, characterized in that: The method of using the grinding liquid film thickness measuring device according to any one of claims 1 to 6 comprises the following steps: S1. During the processing, a light source emits monochromatic light, which is directed parallel to a beam splitter. A portion of the light is reflected by the beam splitter to a first laser reflector, which is then reflected by the first laser reflector and then passes through the beam splitter to be received by the light detector. This portion is defined as the first light. Another portion of the light passes through the beam splitter and the compensation plate, then propagates toward the second laser reflector. After being reflected by the second laser reflector, it passes through the compensation plate and then also propagates toward the light detector and is received by the light detector. This portion of the light is defined as the second light. The first and second light rays are coherent light. The compensation plate is adapted to allow both the first and second light rays to pass through a flat glass of equal thickness three times to avoid an additional optical path difference between the first and second light rays. S2. The interference fringes observed by the light detector are equally spaced. The wavelength of the incident monochromatic light is defined as λ. Then, whenever the first laser reflector moves forward or backward by a distance of λ / 2, the interference fringes move by one, and the number of fringes moved in the field of view is measured as n, then the distance the first laser reflector moves is: ， The optical path difference is: , where d is the spacing between micro grooves; When there is grinding fluid between the second laser reflector and the compensation plate, the optical path difference becomes: , where t is the measured thickness of the grinding fluid; The change in optical path difference is: ； The number of shifts of the interference fringes is: ； The measured thickness of the grinding fluid medium is obtained as: ； This thickness includes the depth of the micro grooves in the diamond grinding wheel, so we need to remove twice the depth of the micro grooves to obtain the final grinding fluid medium thickness: ,in, is the depth of the micro groove.

8. The method for measuring the thickness of a grinding liquid film according to claim 7, characterized in that: After the measurement assembly is installed, the light source emits laser pulses higher than 10,000 Hz through the first optical path tube to calibrate the relative position of the second laser reflector on the grinding wheel and the first optical path tube; when the rotation speed of the diamond grinding wheel is stable, the moment when the second laser reflector is aligned with the first optical path tube is selected as the time to start measurement.

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