A ranging system and a ranging method

Abstract

The present invention discloses a ranging system and a ranging method. The ranging system includes a first laser, a second laser, two dichroic mirrors, a beam expanding unit, a semi-transmissive and semi-reflective mirror, a dispersion objective lens, a displacement stage, and two light intensity detection units. The first dichroic mirror transmits the first wavelength laser emitted by the first laser, reflects the second wavelength laser emitted by the second laser, and after passing through the beam expanding unit, is reflected by the semi-transmissive and semi-reflective mirror to the dispersion objective lens, and is converged by the dispersion objective lens onto the surface of the object to be measured. After the reflected light from the surface of the object to be measured passes through the dispersion objective lens, it is transmitted by the semi-transmissive and semi-reflective mirror and is split into a first light beam and a second light beam by the second dichroic mirror, and the two light intensity detection units respectively detect the light intensities of the two light beams. The embodiments of the present invention perform high-precision detection on the height or microscopic morphology of the object surface, improve the signal-to-noise ratio and detection efficiency, reduce the cost, and can be widely applied to the field of laser ranging technology.

Description

Technical Field

[0001] The present invention relates to the technical field of laser ranging, and in particular to a ranging system and a ranging method. Background Art

[0002] In applications such as industrial production or inspection, there is a need to detect the change in the height of the object surface with high precision. For example: A silicon wafer is a commonly used substrate for gene sequencing chips; by modifying primers on the silicon wafer, the DNA template strand to be detected is captured, and the gene sequencing process is completed by using the technology of sequencing while synthesizing and combining with a microscopic optical system. The microscope has a very high resolution, but a small depth of field. If the relative distance between the objective lens and the silicon wafer changes by a micron level, it is likely to be out of focus, resulting in a blurred imaging result. On the premise of ensuring the relative distance between the objective lens and the silicon wafer, if the surface of the silicon wafer is uneven and the height difference at different positions exceeds the depth of field of the objective lens, it will cause some areas of the imaging field of view to be clear and some areas to be blurred. Therefore, it is a necessary step before manufacturing the sequencing chip to inspect the incoming silicon wafers and ensure that the height difference of the entire silicon wafer meets the requirements for clear imaging. Summary of the Invention

[0003] In view of this, the purpose of the embodiments of the present invention is to provide a ranging system and a ranging method, which can detect the height or microscopic morphology of the object surface with high precision, improve the signal-to-noise ratio and detection efficiency, and reduce the cost.

[0004] In a first aspect, an embodiment of the present invention provides a ranging system, including a first laser, a second laser, a first dichroic mirror, a beam expander unit, a semi-transparent and semi-reflective mirror, a dispersive objective lens, a displacement stage, a second dichroic mirror, a first light intensity detection unit, and a second light intensity detection unit; the first dichroic mirror transmits the first-wavelength laser emitted by the first laser, and the first dichroic mirror reflects the second-wavelength laser emitted by the second laser, and the first-wavelength laser and the second-wavelength laser form a combined light at the first dichroic mirror; after passing through the beam expander unit, the combined light is reflected by the semi-transparent and semi-reflective mirror to the dispersive objective lens and converges to the surface of the object to be measured through the dispersive objective lens; the reflected light from the surface of the object to be measured passes through the dispersive objective lens, is transmitted by the semi-transparent and semi-reflective mirror, and is split into a first light beam and a second light beam by the second dichroic mirror; the light intensity of the first light beam is measured by the first light intensity detection unit, and the light intensity of the second light beam is measured by the second light intensity detection unit; the object to be measured is fixed on the displacement stage.

[0005] Optionally, the dispersive objective lens includes a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis direction; wherein, the first lens, the second lens, and the third lens all have positive optical power, and the fourth lens has negative optical power.

[0006] Optionally, the first lens satisfies the following relationship:

[0007] 2.1 < f L1 / f < 2.4

[0008] where f L1 represents the focal length of the first lens, and f represents the focal length of the dispersion objective lens.

[0009] Optionally, the second lens satisfies the following relationship:

[0010] 1.76 < f L2 / f < 1.95

[0011] where f L2 represents the focal length of the second lens, and f represents the focal length of the dispersion objective lens.

[0012] Optionally, the third lens satisfies the following relationship:

[0013] 1.58 < f L3 / f < 1.69

[0014] where f L3 represents the focal length of the third lens, and f represents the focal length of the dispersion objective lens.

[0015] Optionally, the fourth lens satisfies the following relationship:

[0016] -1.13 < f L4 / f < 0.94

[0017] where f L4 represents the focal length of the fourth lens, and f represents the focal length of the dispersion objective lens.

[0018] Optionally, the first light intensity detection unit and / or the second light intensity detection unit includes a converging lens, a pinhole, and a photodiode. The converging lens converges the incident light beam onto the pinhole, and the photodiode measures the light intensity after the incident light is converged.

[0019] In a second aspect, an embodiment of the present invention provides a ranging method applied to the above ranging system, including:

[0020] Starting the first laser, the second laser, the first light intensity detection unit, and the second light intensity detection unit;

[0021] Move the dispersion objective lens in the vertical direction along the surface of the object to be measured to determine the first height of the dispersion objective lens corresponding to the intensity peak of the first light beam and the second height of the dispersion objective lens corresponding to the intensity peak of the second light beam, and determine the intermediate height of the dispersion objective lens according to the first height and the second height of the dispersion objective lens;

[0022] Move the dispersion objective lens to the intermediate height of the dispersion objective lens and keep it unchanged;

[0023] Use the displacement stage to scan the surface of the object to be measured to obtain the light intensities of the first light beam and the second light beam at different positions, and calculate the distances of different positions on the surface of the object to be measured according to the light intensity of the first light beam, the light intensity of the second light beam and a preset third curve.

[0024] Optionally, the preset third curve is obtained by the following method:

[0025] Determine a first curve corresponding to the change in the light intensity of the first light beam with the distance on the surface of the object to be measured;

[0026] Determine a second curve corresponding to the change in the light intensity of the second light beam with the distance on the surface of the object to be measured;

[0027] Determine the third curve according to the first curve and the second curve.

[0028] Optionally, the method further includes:

[0029] Determine the dispersion distance of the dispersion objective lens for the first-wavelength laser and the second-wavelength laser according to the detection range of the surface of the object to be measured.

[0030] Implementing the embodiments of the present invention includes the following beneficial effects: In this embodiment, two lasers are used to generate two test lasers. The two test lasers are focused on the surface of the object to be measured through a dispersion objective lens. The reflected light from the surface of the object to be measured is split into two beams of light by a dichroic mirror after passing through the dispersion objective lens. The two beams of light are respectively measured by two light intensity detection units. The height or microscopic morphology of the object surface is detected with high precision according to the light intensities measured by the two light intensity detection units; in addition, two single-wavelength lasers are used as detection lights. Under the same optical power, the energy of each wavelength is higher than the energy of a single wavelength in the white light source used in the traditional spectral confocal system, and the signal-to-noise ratio of the detected light intensity signal is better; the dichroic mirror splits the reflected light, with less waste of light energy, reduced exposure time, and high detection efficiency; the two light intensity detection units respectively test the two beams of reflected light, and the light intensity signal acquisition rate is fast; the cost and debugging difficulty of the entire ranging system are low, which is convenient for popularization and use. Description of the Drawings

[0031] Figure 1It is a schematic structural diagram of a ranging system provided by an embodiment of the present invention;

[0032] Figure 2 It is an optical path structure diagram of a dispersion objective lens provided by an embodiment of the present invention;

[0033] Figure 3 It is a relationship diagram between the laser wavelength and the working distance of the dispersion objective lens provided by an embodiment of the present invention;

[0034] Figure 4 It is a spot diagram of three wavelengths of a dispersion objective lens provided by an embodiment of the present invention;

[0035] Figure 5 It is a schematic step flow diagram of a ranging method provided by an embodiment of the present invention;

[0036] Figure 6 It is a curve graph of the distance change of the object to be measured corresponding to the laser intensities of two wavelengths provided by an embodiment of the present invention;

[0037] Figure 7 It is a partial enlarged view of the distance change curve of the object to be measured corresponding to the laser intensities of two wavelengths provided by an embodiment of the present invention;

[0038] Figure 8 It is a change curve graph of the distance change curve of the object to be measured after the arithmetic processing of the laser intensities of two wavelengths provided by an embodiment of the present invention. Detailed implementation manners

[0039] The following further elaborates the present invention in detail in conjunction with the accompanying drawings and specific embodiments. For the step numbers in the following embodiments, they are only set for the convenience of elaboration and explanation, and no limitation is imposed on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0040] Spectral confocal measurement technology utilizes the dispersion principle, that is, the focal points of lights with different wavelengths are different, to establish the corresponding relationship between the wavelength and the focal plane position. When the object plane corresponds to the focal point of a certain wavelength of light, the light of this wavelength satisfies the object-image conjugate condition of the optical system and can be more effectively coupled into the optical fiber, thereby being detected by the spectrometer. By analyzing the wavelength of the strongest signal light in the spectrometer, the relative distance between the objective lens and the sample can be quantitatively calculated, thereby realizing the high-precision analysis of the height and microscopic morphology of the sample.

[0041] An embodiment of the present invention provides a ranging system, which includes a first laser, a second laser, a first dichroic mirror, a beam expander, a beam splitter, a dispersive objective lens, a displacement stage, a second dichroic mirror, a first light intensity detection unit, and a second light intensity detection unit; the first dichroic mirror transmits the first wavelength laser emitted by the first laser, and the first dichroic mirror reflects the second wavelength laser emitted by the second laser, and the first wavelength laser and the second wavelength laser form combined light at the first dichroic mirror; after passing through the beam expander, the combined light is reflected by the beam splitter to the dispersive objective lens and converges on the surface of the object to be measured through the dispersive objective lens; after the reflected light from the surface of the object to be measured passes through the dispersive objective lens, it is transmitted by the beam splitter and is split into a first light beam and a second light beam by the second dichroic mirror; the light intensity of the first light beam is measured by the first light intensity detection unit, and the light intensity of the second light beam is measured by the second light intensity detection unit; the object to be measured is fixed on the displacement stage.

[0042] It should be noted that the first laser and the second laser are determined according to actual applications, such as according to the detection range of the object to be measured, and no specific limitations are made in this embodiment.

[0043] Specifically, the function of the dichroic mirror is to transmit or reflect light of two wavelengths, the function of the beam expander is to expand the incident light, the function of the dispersive objective lens is to focus or disperse two different wavelength lasers, the function of the displacement stage is to complete the scanning of the entire surface height of the object to be measured by the optical system, and the function of the light intensity detection unit is to preprocess the optical signal and convert it into an electrical signal to detect the light intensity.

[0044] Optionally, the first light intensity detection unit and / or the second light intensity detection unit includes a focusing lens, a pinhole, and a photodiode. The focusing lens focuses the incident light beam onto the pinhole, and the photodiode measures the light intensity after the incident light is focused.

[0045] It should be noted that the function of the focusing lens is to focus the incident light beam, the function of the pinhole is to filter out stray light and improve the signal-to-noise ratio, and the photodiode converts the received optical signal into an electrical signal.

[0046] Specifically, refer to Figure 1, the wavelength of laser 1 is 660 nm, and the wavelength of laser 2 is 488 nm. The light emitted by the two lasers first reaches dichroic mirror 3. Dichroic mirror 3 transmits light in the 660 nm band and reflects light in the 488 nm band; therefore, the light emitted by the two lasers is integrated into a combined beam with the same directivity after passing through dichroic mirror 3. The diameter of the combined beam increases after passing through beam expander unit 4, is reflected by beam splitter 5 and enters dispersion objective 6, and then converges on the surface of the object under test 7. The object under test 7 is fixed on electric displacement stage 8 by means of vacuum adsorption. The illumination light converging on the object under test 7 is reflected by the silicon wafer, passes through dispersion objective 6 again, and is split into two beams of light by dichroic mirror 9 after passing through beam splitter 5. Among them, the 660 nm laser passes through dichroic mirror 9 and is converged on pinhole 11 by a converging lens 10 with a focal length of 200 mm. The laser signal after spatial filtering is received by photodiode 12; among them, the 488 nm laser is reflected by dichroic mirror 9 and is converged on pinhole 14 by a converging lens 13 with a focal length of 200 mm, and then is received by photodiode 15.

[0047] Optionally, the dispersion objective includes a first lens, a second lens, a third lens, and a fourth lens arranged in sequence along the optical axis direction; wherein, the first lens, the second lens, and the third lens all have positive optical power, and the fourth lens has negative optical power.

[0048] It should be noted that the first lens, the second lens, and the third lens all generate negative spherical aberration, and the fourth lens generates positive spherical aberration to balance the negative spherical aberration generated by the first lens to the third lens.

[0049] Optionally, the first lens satisfies the following relationship:

[0050] 2.1 < f L1 / f < 2.4

[0051] wherein, f L1 represents the focal length of the first lens, and f represents the focal length of the dispersion objective.

[0052] Optionally, the second lens satisfies the following relationship:

[0053] 1.76 < f L2 / f < 1.95

[0054] wherein, f L2 represents the focal length of the second lens, and f represents the focal length of the dispersion objective.

[0055] Optionally, the third lens satisfies the following relationship:

[0056] 1.58 < f L3 / f < 1.69

[0057] wherein, f L3 represents the focal length of the third lens, and f represents the focal length of the dispersion objective lens.

[0058] Optionally, the fourth lens satisfies the following relationship:

[0059] -1.13 < f L4 / f < 0.94

[0060] wherein, f L4 represents the focal length of the fourth lens, and f represents the focal length of the dispersion objective lens.

[0061] Specifically, referring to Figure 2 and Table 1, Figure 2 wherein L1 - L4 respectively represent the first lens to the fourth lens, S1 - S8 respectively represent different surface numbers, and Table 1 includes the specific parameters of each surface in the first lens to the fourth lens.

[0062] Table 1

[0063] Surface number Radius of curvature / mm Thickness / mm Refractive index Abbe number 1 26.864 2.995 1.61 56.7 2 -27.857 1.392 3 10.953 1 1.55 63.5 4 -156.695 0.1 5 7.873 1.187 1.66 57.4 6 28.469 0.417 7 -101.975 2.939 1.92 18.9 8 10.537 4.423

[0064] It should be noted that in this embodiment, a dispersion design is performed for two wavelengths. Compared with the dispersion objective lens of the continuous band used in traditional spectral confocal microscopy, its structure is simple and the cost is lower. Secondly, the dispersion objective lens in this embodiment is designed as an infinity conjugate to meet the requirements of the subsequent dichroic mirror splitting optical path. Finally, if the required detection range is small, the designed NA of the dispersion objective lens is greater than 0.4 to reduce its depth of field and increase the sensitivity to the height change of the silicon wafer.

[0065] The object surface ranging system designed based on the principle of spectral confocal in this embodiment adopts a detection unit composed of a dichroic mirror and two photodiodes, as well as an illumination unit composed of a dual-wavelength laser. Compared with the traditional spectral confocal system that uses a spectrometer as the detection unit and a white light source as the illumination unit, it has the following advantages: First, the photodiode belongs to a single-point detector. Compared with the multi-point detector used in the spectrometer, the acquisition rate is faster, and the detection of the entire surface of the object to be measured can be completed more quickly and effectively. Second, the traditional spectrometer needs to use a grating for spectral splitting, and the zero-order and high-order diffractions of the grating will waste a considerable part of the energy of the signal light. The dichroic mirror used in this embodiment hardly wastes light energy during spectral splitting. Under the condition of the same excitation light power, the signal-to-noise ratio of the detection unit in this embodiment will be significantly better than that of the spectrometer. When the light source brightness cannot be further increased and the reflectivity of the sample to be measured is low, in order to ensure a sufficient signal-to-noise ratio, the detector in the spectrometer needs to extend the exposure time, and this operation will significantly reduce the frame rate of the detector and affect the detection efficiency. Third, the illumination unit of this embodiment is composed of a dual-wavelength laser. Under the condition of the same output light power, the energy of each wavelength is higher than the energy of a single wavelength in the white light source used in the traditional spectral confocal unit. Therefore, the detection signal-to-noise ratio of this embodiment is better. In addition, the cost and alignment difficulty of the detection unit of the present invention are significantly better than those of the spectral confocal system using a spectrometer as the detector.

[0066] Optionally, the dispersion distance of the dispersion objective in the ranging system is determined by the following method:

[0067] S010. Determine the dispersion distance of the dispersion objective for the first wavelength laser and the second wavelength laser according to the detection range of the surface of the object to be measured.

[0068] The dispersion distance of the dispersion objective for the two detection laser wavelengths is determined according to the detection range of the object to be detected. For example, if the detection range of the object to be detected is 7um, the dispersion distance of the dispersion objective for the two detection laser wavelengths is 20um. Refer to Figure 3 , different combinations of laser wavelengths can achieve different dispersion distance designs.

[0069] In a specific embodiment, refer to Figure 4 , the spot diagrams of the dispersion objective at wavelengths of 488nm, 588nm, and 660nm, wherein the diameter of the spot diagram at the 660nm wavelength is 2.00um; from Figure 4 it can be seen that the size of the converging spot is smaller than the Airy disk size under the three wavelength conditions, indicating that the spherical aberration of the objective lens is well corrected and the image quality is close to the diffraction limit.

[0070] Refer to Figure 5 This embodiment of the present invention provides a ranging method, which is applied to the above ranging system and includes:

[0071] S100. Activate the first laser, the second laser, the first light intensity detection unit, and the second light intensity detection unit.

[0072] Specifically, the lasers and the light intensity detection units are active devices and need to be powered on before use.

[0073] S200. Move the dispersion objective lens in the vertical direction of the surface of the object to be measured to determine the first height of the dispersion objective lens corresponding to the intensity peak of the first light beam and the second height of the dispersion objective lens corresponding to the intensity peak of the second light beam, and determine the intermediate height of the dispersion objective lens based on the first height and the second height of the dispersion objective lens.

[0074] Specifically, determine the intermediate intensity peak as the actual working range of the ranging system based on the intensity peak of the first light beam and the intensity peak of the second light beam; the intermediate value of the first intensity peak and the second intensity peak can be used as the intermediate intensity peak.

[0075] Specifically, determine the actual working starting range of the dispersion objective lens based on the first height and the second height of the dispersion objective lens; the intermediate value of the first height and the second height of the dispersion objective lens can be used as the intermediate height of the dispersion objective lens.

[0076] S300. Move the dispersion objective lens to the intermediate height of the dispersion objective lens and keep it unchanged.

[0077] S400. Scan the surface of the object to be measured with the displacement stage to obtain the light intensities of the first light beam and the second light beam at different positions, and calculate the distances of different positions on the surface of the object to be measured based on the light intensity of the first light beam, the light intensity of the second light beam, and a preset third curve.

[0078] It should be noted that the preset third curve is a relational function of the light intensity of the laser with the first wavelength, the light intensity of the laser with the second wavelength, and the distance of the surface of the object to be measured. The relational function is determined according to the actual application and is not specifically limited in this embodiment.

[0079] Optionally, the preset third curve is obtained by the following method:

[0080] S410. Determine the first curve corresponding to the change in the light intensity of the first light beam with the distance of the surface of the object to be measured;

[0081] S420. Determine the second curve corresponding to the change in the light intensity of the second light beam with the distance of the surface of the object to be measured;

[0082] S430. Determine the third curve based on the first curve and the second curve.

[0083] Specifically, the specific method for determining the third curve based on the first curve and the second curve is determined according to the actual application, and this embodiment does not make specific limitations. For example, the third curve is obtained by dividing the first curve by the second curve and then fitting, or by multiplying the first curve by the second curve and then fitting, etc.

[0084] In a specific embodiment, refer to Figure 6 , the curves of the return light intensity monitored by the 660nm signal detector and the 488nm signal detector varying with the height of the silicon wafer. As can be seen from Figure 6 , the curve of the laser energy intensity varying with the height of the silicon wafer is a function similar to a Gaussian curve, and the focal position is the peak of this curve. Among them, the distance between the peaks of 488nm and 660nm is about 20um, which is consistent with the design parameters that the detection range of the above object to be detected is 7um and the dispersion distance of the dispersion objective for the two detection laser wavelengths is 20um.

[0085] At the middle position of the peak, that is, about 10um away from the peak signal position, the actual working range of this silicon wafer height measurement system is within ±8um of this position. The curves of the return light intensity monitored by the 660nm signal detector and the 488nm signal detector varying with the height of the silicon wafer are as shown in Figure 7 . Dividing the two curves can obtain a curve that monotonically changes with the height of the silicon wafer, as shown in Figure 8 . Among them, the single points on the curve are the calculated values of the division of the signals of the two detectors when the height of the silicon wafer changes at 1um intervals, and the curve is the fitting curve of the calculated values of the signals of the two detectors. The curve equation is: y = 6.56 * exp(-x / 1.135) + 5.879 * exp(-x / 10.844) + 4.513 * exp(-x / 0.122) + 0.904. Among them, x is the calculated value of the division of the signals of the two detectors, and the corresponding height y of the silicon wafer can be obtained according to this equation. Using R 2 = regression deviation / total deviation = ∑i(Yi - _y) 2 / ∑i(yi - _y) 2 to evaluate the goodness of fit of the fitting. The R 2 of the fitting curve is 0.9996, indicating that the fitting degree of this curve is very high.

[0086] Implementing the embodiments of the present invention includes the following beneficial effects: In this embodiment, two lasers are used to generate two test lasers. The two test lasers are focused on the surface of the object to be measured through a dispersion objective lens. The reflected light on the surface of the object to be measured passes through the dispersion objective lens and is then split into two beams of light by a dichroic mirror. The two beams of light are respectively measured by two light intensity detection units. The height or microscopic topography of the object surface is detected with high precision according to the light intensities measured by the two light intensity detection units. In addition, two single-wavelength lasers are used as detection lights. Under the same optical power condition, the energy of each wavelength is higher than the energy of a single wavelength in the white light source used in the traditional spectral confocal system, and the signal-to-noise ratio of the detected light intensity signal is better. The dichroic mirror splits the reflected light, with less waste of light energy, reduced exposure time, and high detection efficiency. The two light intensity detection units respectively test the two beams of reflected light, and the light intensity signal acquisition rate is fast. The cost and debugging difficulty of the entire ranging system are low, which is convenient for popularization and use.

[0087] The above is a specific description of the preferred embodiment of the present invention, but the present invention is not limited to the described embodiment. Those skilled in the art can make various equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A ranging method, characterized in that, The ranging system includes a first laser, a second laser, a first dichroic mirror, a beam expander unit, a semi-transmissive and semi-reflective mirror, a dispersive objective lens, a displacement stage, a second dichroic mirror, a first light intensity detection unit and a second light intensity detection unit. The first dichroic mirror transmits the first-wavelength laser emitted by the first laser and reflects the second-wavelength laser emitted by the second laser. The first-wavelength laser and the second-wavelength laser form a combined light at the first dichroic mirror. After passing through the beam expander unit, the combined light is reflected by the semi-transmissive and semi-reflective mirror to the dispersive objective lens and converges on the surface of the object to be measured through the dispersive objective lens. After the reflected light from the surface of the object to be measured passes through the dispersive objective lens, it is transmitted by the semi-transmissive and semi-reflective mirror and divided into a first light beam and a second light beam by the second dichroic mirror. The light intensity of the first light beam is measured by the first light intensity detection unit, and the light intensity of the second light beam is measured by the second light intensity detection unit. The object to be measured is fixed on the displacement stage. The ranging method includes: Starting the first laser, the second laser, the first light intensity detection unit and the second light intensity detection unit; Moving the dispersive objective lens in the vertical direction of the surface of the object to be measured to determine the first height of the dispersive objective lens corresponding to the intensity peak of the first light beam and the second height of the dispersive objective lens corresponding to the intensity peak of the second light beam, and determining the intermediate height of the dispersive objective lens according to the first height and the second height of the dispersive objective lens; Moving the dispersive objective lens to the intermediate height of the dispersive objective lens and keeping it unchanged; Scanning the surface of the object to be measured with the displacement stage to obtain the light intensities of the first light beam and the second light beam at different positions, and calculating the distances at different positions on the surface of the object to be measured according to the light intensity of the first light beam, the light intensity of the second light beam and a preset third curve.

2. The method according to claim 1, characterized in that, The preset third curve is obtained by the following method: Determining a first curve corresponding to the change of the light intensity of the first light beam with the distance on the surface of the object to be measured; Determining a second curve corresponding to the change of the light intensity of the second light beam with the distance on the surface of the object to be measured; Determining the third curve according to the first curve and the second curve.

3. The method according to claim 1, characterized in that, The method further includes: Determining the dispersion distance of the dispersive objective lens for the first-wavelength laser and the second-wavelength laser according to the detection range of the surface of the object to be measured.

4. The method according to claim 1, characterized in that, The dispersive objective lens includes a first lens, a second lens, a third lens and a fourth lens arranged in sequence along the optical axis direction. Among them, the first lens, the second lens and the third lens all have positive optical power, and the fourth lens has negative optical power.

5. The method according to claim 4, characterized in that, The first lens satisfies the following relationship: 2.1 < f L1 / f < 2.4 where f L1 represents the focal length of the first lens, and f represents the focal length of the dispersion objective lens.

6. The method according to claim 4, characterized in that, The second lens satisfies the following relationship: 1.76 < f L2 / f < 1.95 Among them, f L2 represents the focal length of the second lens, and f represents the focal length of the dispersion objective lens.

7. The method according to claim 4, characterized in that, The third lens satisfies the following relationship: 1.58 < f L3 / f < 1.69 Among them, f L3 represents the focal length of the third lens, and f represents the focal length of the dispersion objective lens.

8. The method according to claim 4, characterized in that, The fourth lens satisfies the following relationship: -1.13 < f L4 / f < 0.94 Among them, f L4 represents the focal length of the fourth lens, and f represents the focal length of the dispersion objective lens.

9. The method according to claim 1, characterized in that, The first light intensity detection unit and / or the second light intensity detection unit includes a converging lens, a pinhole and a photodiode. The converging lens converges the incident light beam to the pinhole, and the photodiode measures the light intensity after the incident light is converged.

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