Surface profile measurement system for counteracting environmental noise introduced by optical path

Abstract

The invention discloses a surface profile measurement system for counteracting ambient noise introduced by an optical path, and the system comprises a light source which comprises a first light source and a second light source with different wavelengths; the interference light path is used for obtaining an interference pattern of the measuring arm and the reference arm; the optical path compensation module is used for receiving the interference phase change of the second light source passing through the interference light path, adjusting the optical path difference of the interference light path based on the interference phase change, and generating the optical path difference which is equivalent to the interference phase change quantity but is opposite to the interference phase change quantity, so as to compensate the environmental noise generated in the light path; and the signal processing system is used for carrying out pixel-by-pixel time-frequency analysis on the pattern interfered by the to-be-tested sample to obtain the contour of the to-be-tested sample. Therefore, noise caused by environmental disturbance in a non-common-path optical path can be counteracted, so that high-precision, high-speed-measurement and environment-interference-resistant surface topography measurement is realized, and the method is used for a coherent scanning interference technology for micro-nano-scale precision measurement.

Description

Technical Field

[0001] The invention relates to a surface profile measurement system for offsetting environmental noise introduced by an optical path, and relates to the technical field of optical profile measurement. Background Art

[0002] High-precision surface topography measurement has extremely important scientific significance and practical value in the fields of industrial manufacturing, semiconductors, materials science, etc. It is not only related to the strict control of product quality in industrial production, but also directly affects the core links such as the research and development of new materials, device performance optimization, failure analysis and prediction. For example, the fine structure of aerospace engine blades affects its aerodynamic performance, and high-precision surface topography measurement is required to ensure that the geometric accuracy and roughness of the blades meet the design requirements; in the chip manufacturing process, high-precision surface topography measurement is a necessary detection step for polishing, epitaxy, lithography, packaging and other processes, and is the key to ensuring chip performance.

[0003] Coherent scanning interferometer is one of the most common three-dimensional topography measurement devices, used for nanometer-level non-contact measurement of micro-nano devices. This interferometer uses low-coherence light as the light source, and generally scans an interferometer arm to find the distance that makes the optical path difference between the two arms zero (corresponding to the position with the highest contrast of the interference fringes) to determine the height of each point on the surface. Its height measurement accuracy depends on the coherence length of the light source and the mechanical scanning accuracy, which can reach the nanometer level in a short range. The measurable height is determined by the working distance of the objective lens and the height scanning range of the scanning stage.

[0004] In recent years, a coherent scanning interferometer technology based on scanning the repetition frequency of femtosecond lasers has emerged in the prior art. This technology does not require mechanical scanning of the interference optical path and can achieve long-distance, large field of view, high-speed measurement, and high-precision surface measurement. In order to achieve the conversion from frequency scanning to height scanning, this method adopts the design of Michelson interferometer, and requires a large optical path difference between the measuring arm and the reference arm, which makes it very sensitive to environmental noise and difficult to truly achieve high-precision measurement. Therefore, realizing a femtosecond laser coherent scanning interferometer measurement system that is insensitive to environmental noise has important practical significance for precision measurement. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, in view of the above problems, the purpose of the present invention is to provide a surface profile measurement system that offsets the environmental noise introduced by the optical path, which can offset the environmental noise introduced by the asymmetric optical path, thereby achieving high-precision, high-speed, and environmentally resistant surface topography measurement.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a surface profile measurement system for offsetting environmental noise introduced by an optical path, the system comprising a light source, an interference optical path, an optical path compensation module and a signal processing system; The light source comprises a first light source and a second light source with different wavelengths, wherein the first light source is used to measure the morphology of the surface of the sample to be measured, and the second light source is used to measure the environmental noise in the interference light path; The interference optical path is used to obtain a pattern of interference between the measuring arm and the reference arm; The optical path compensation module is used to receive the interference phase change of the second light source passing through the interference optical path, and adjust the optical path difference of the interference optical path arm based on the interference phase change to generate an optical path difference equivalent to but in the opposite direction of the interference phase change, thereby compensating for the environmental noise generated in the optical path; The signal processing system is used to perform pixel-by-pixel time-frequency analysis on the interference pattern of the sample to be tested to obtain the contour of the sample to be tested.

[0007] In some possible embodiments, the first light source is a femtosecond laser, and the femtosecond laser is a broadband coherent light source with adjustable repetition frequency.

[0008] In some possible embodiments, the second light source is a continuous laser, and the continuous laser is a frequency-stable narrow-linewidth laser.

[0009] In some possible embodiments, the interference optical path includes a beam combiner, a beam splitter, a dichroic mirror, a reflector, and an image acquisition module; The beam combiner is used to combine femtosecond laser and continuous laser of different wavelengths into one beam and send it to the beam splitter; a part of the light emitted by the beam splitter is used as the measuring arm to illuminate the sample to be measured; another part of the light emitted by the beam splitter is emitted to the reflector as the reference arm; the light reflected by the reflector and the sample to be measured enters the beam splitter again for coupling and is sent to the dichroic mirror; the continuous laser emitted by the dichroic mirror is separated and enters the optical path compensation module; the femtosecond laser emitted by the dichroic mirror enters the image acquisition module; the image acquisition module acquires the pattern of interference between the measuring arm and the reference arm.

[0010] In some possible embodiments, the optical path compensation module includes a detector, a motion unit and a control unit, wherein the motion unit is connected to the reflector; The detector is used to detect the interference signal of the continuous laser; The control unit controls the reflection mirror to move along the optical axis through the motion unit according to the interference phase fluctuation of the continuous laser light, suppresses the interference phase fluctuation, and thus compensates for the noise generated in the optical path.

[0011] In a second aspect, the present invention also provides a surface profile measurement system for offsetting environmental noise introduced by an optical path, comprising: a light source, an interference optical path, an optical path compensation module and a signal processing system; The light source comprises a first light source and a second light source with different wavelengths, the first light source and the second light source are divided into two paths through a dual-wavelength coupler, one path is emitted through a first optical fiber as a measurement light, and the other path is emitted after being delayed by a second optical fiber as a reference light, the two paths of light with different time delays are relatively transmitted in space and enter the interference optical path, wherein the first optical fiber and the second optical fiber have different lengths; The interference optical path is used to obtain a pattern of interference between the measuring arm and the reference arm; The optical path compensation module is used to receive the interference phase change of the second light source passing through the interference optical path, and control the length change of the first optical fiber or the second optical fiber based on the interference phase change to generate an optical path difference equivalent to but in the opposite direction of the interference phase change, thereby compensating for the environmental noise generated in the optical path; The signal processing system is used to perform pixel-by-pixel time-frequency analysis on the interference pattern of the sample to be tested to obtain the contour of the sample to be tested.

[0012] In some possible embodiments, the first light source is a femtosecond laser, and the second light source is a single-frequency laser.

[0013] In some possible embodiments, the function of the second optical fiber is to make the optical path difference between the reference arm and the measurement arm of the interference optical path be L pp of M times, among which, L pp is the spatial interval of the femtosecond laser output pulses, M is an integer. When the repetition frequency of the femtosecond laser is scanned, if the optical path difference is exactly equal to ML pp Each pulse in one arm will be M The pulses interfere with each other, and the relative height of the point can be determined based on the repetition frequency at this time.

[0014] In some possible embodiments, the optical path compensation module includes a detector, a servo controller and a length controller; The detector is used to detect the interference signal of the single-frequency laser; The servo controller sets the signal intensity when the interference phase is π / 2 as the reference point, and controls the length controller to adjust the length of the second optical fiber according to the interference signal of the single-frequency laser to lock the optical path difference of the interference optical path, thereby compensating for the noise generated in the optical path.

[0015] In some possible embodiments, the interference module includes a beam splitter, a first dichroic mirror, a first lens, a second dichroic mirror, a second lens, and an image acquisition module; The measuring light is reflected by the beam splitter and irradiates the sample to be measured through the first dichroic mirror. A part of the light returning from the sample to be measured passes through the beam splitter and enters the image acquisition module through the first lens, the second dichroic mirror and the second lens. The reference light is reflected by the beam splitter and enters the image acquisition module through the first lens, the second dichroic mirror and the second lens to interfere with the measuring light. The image acquisition module collects a pattern of interference between the measuring light and the reference light. The second dichroic mirror is used to separate the single-frequency laser and the femtosecond laser after the measuring arm and the reference arm are combined. The separated single-frequency laser is detected by the detector.

[0016] Due to the adoption of the above technical solution, the present invention has the following characteristics: the present invention is provided with an optical path compensation module for receiving the interference phase change of the second light source through the interference optical path, adjusting the optical path difference of the interference optical path based on the interference phase change, generating an optical path difference equivalent to but inverse to the interference phase change, thereby compensating for the environmental noise generated in the optical path. Therefore, the present invention is insensitive to environmental interferences such as airflow and vibration, and can offset the environmental noise introduced by the asymmetric optical path, thereby achieving high-precision, high-speed, and environmentally-interference-resistant surface topography measurement. Therefore, the present invention can easily achieve a large field of view of more than centimeters, and the measurement accuracy can still reach nanometers when performing vertical scanning with a micron-level step length, and can be widely used in coherent scanning interference for micro-nano-level precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Throughout the accompanying drawings, the same reference numerals are used to represent the same components. In the accompanying drawings: Figure 1 A schematic diagram of the structure of a surface profile measurement system according to an embodiment of the present invention; Figure 2 FIG. 4 is a schematic structural diagram of a surface profile measurement system according to another embodiment of the present invention. DETAILED DESCRIPTION

[0018] It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and / or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and / or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

[0019] Although the terms first, second, third, etc. can be used in the text to describe multiple elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can only be used to distinguish an element, component, region, layer or section from another region, layer or section. Unless the context clearly indicates, terms such as "first", "second" and other numerical terms do not imply order or sequence when used in the text. Therefore, the first element, component, region, layer or section discussed below can be referred to as the second element, component, region, layer or section without departing from the teaching of the example embodiments.

[0020] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside", "outside", "inner side", "outer side", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0021] Because the existing femtosecond laser coherent scanning interferometry measurement system is very sensitive to environmental noise. The present invention provides a surface profile measurement system for offsetting the environmental noise introduced by the optical path, including a light source, the light source including a first light source and a second light source with different wavelengths; an interference optical path, used to obtain a pattern of interference between the measuring arm and the reference arm; an optical path compensation module, used to receive the interference phase change of the second light source through the interference optical path, and adjust the optical path difference of the interference optical path based on the interference phase change, to generate an optical path difference equivalent to but inverse to the interference phase change, thereby compensating for the environmental noise generated in the optical path; a signal processing system, used to perform pixel-by-pixel time-frequency analysis on the pattern of interference of the sample to be measured, and obtain the profile of the sample to be measured. Therefore, the present invention can offset the noise brought by environmental disturbances in non-common path optical paths, thereby realizing high-precision, high-speed measurement, and environmental interference-resistant surface morphology measurement, and is used for coherent scanning interferometry technology for micro-nano precision measurement.

[0022] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0023] Embodiment 1: Figure 1 As shown, the surface profile measurement system for offsetting the environmental noise introduced by the optical path provided in this embodiment includes a light source 1, an interference optical path 2, an optical path compensation module 3 and a signal processing system 4.

[0024] The light source 1 includes a femtosecond laser 11 and a continuous laser 12, wherein the femtosecond laser 11 is a broadband coherent light source with adjustable repetition frequency, which is used to measure the surface morphology of the sample 5 to be measured; the continuous laser 12 is a narrow-linewidth laser with stable frequency, and its wavelength is different from that of the femtosecond laser 11, which is used to measure the environmental noise in the interference light path.

[0025] Interference optical path 2 realizes the surface morphology measurement of the sample through the full-field interference fringes of the measuring arm and the reference arm.

[0026] The optical path compensation module 3 is used to receive the interference signal generated after the continuous laser passes through the interference optical path 2, and the obtained interference phase change is used as input to adjust the position of the reflector in the interference optical path 2 along the optical axis to generate an optical path difference that is equivalent to but opposite to the measured phase change, thereby compensating for the noise generated in the optical path due to atmospheric disturbances, mechanical vibrations and other factors. It should be noted that in this embodiment, the position of the reflector in the reference arm in the interference optical path 2 along the optical axis is adjusted to thereby adjust the optical path difference of the interference optical path. This is taken as an example, and is not limited to this. The measuring arm in the interference optical path 2 can also be adjusted to thereby adjust the optical path difference of the interference optical path, and can be selected as needed.

[0027] The signal processing system 4 is used to perform pixel-by-pixel time-frequency analysis on the obtained continuous interference pattern of the sample 5 to be tested, and obtain the contour information of the sample 5 to be tested after filtering and peak detection algorithm.

[0028] In a preferred embodiment of the present invention, the femtosecond laser 11 may be a mode-locked laser, an electro-optical modulated optical frequency comb, etc., which is taken as an example but not limited thereto.

[0029] In a preferred embodiment of the present invention, the continuous laser 12 can be a semiconductor laser, a dual-frequency laser, etc., which is taken as an example but not limited thereto.

[0030] In a preferred embodiment of the present invention, the interference optical path 2 may adopt a Michelson interferometer, which is taken as an example but not limited to this.

[0031] Furthermore, the interference optical path 2 includes a beam combiner 21, a beam splitter 22, a dichroic mirror 23, a reflector 24 and an image acquisition module 25; the beam combiner 21 is used to combine the femtosecond laser and the continuous laser of different wavelengths emitted by the femtosecond laser 11 and the continuous laser 12 into one beam and send it to the beam splitter 22, a part of the light emitted by the beam splitter 22 is used as a measuring arm to irradiate the sample 5 to be measured, and another part of the light emitted by the beam splitter 22 is emitted to the reflector 24 as a reference arm, and the light reflected by the reflector 24 and the sample 5 to be measured enters the beam splitter 22 again for coupling and is sent to the dichroic mirror 23, the continuous laser emitted by the dichroic mirror 23 is separated and enters the optical path compensation module 3, and the femtosecond laser emitted by the dichroic mirror 23 enters the image acquisition module 25.

[0032] In a preferred embodiment of the present invention, the optical path compensation module 3 includes a detector 31, a motion unit 32 and a control unit.

[0033] The motion unit 32 is used to connect to the reflector 24. The motion unit 32 is controlled by the control unit to adjust the position of the reflector 24 in the interference optical path 2 along the optical axis, thereby compensating for noise generated in the optical path due to atmospheric disturbances, mechanical vibrations and other factors.

[0034] The detector 31 is used to detect the interference signal of the continuous laser. When there is air disturbance, table vibration and other environmental noise in the interference optical path, the optical path of the interference optical path 2 will become unstable, resulting in phase fluctuation of the interference signal. The motion unit 32 controls the position of the reflector 24 along the optical axis according to the interference phase fluctuation of the continuous laser to suppress the interference phase fluctuation. Since the femtosecond laser and the continuous laser are almost completely on the same path, the optical path difference of the femtosecond laser interference is synchronously stabilized, thereby achieving the effect of compensating for the environmental noise in the interference optical path.

[0035] The measuring principle of the surface profile measurement system for offsetting the environmental noise introduced by the optical path of the present invention is as follows: the femtosecond laser 11 is used to measure the morphology of the surface of the sample 5 to be measured, and the continuous laser 12 is used to measure the environmental noise in the interference optical path 2. After the two beams of light are combined, they enter the beam splitter 22 at the same time and are divided into transmitted light and reflected light. The transmitted light illuminates the reflector 24, and the reflected light illuminates the sample 5 to be measured. Among them, the optical path difference between the measuring arm and the reference arm is approximately a non-zero integer multiple of the interval between the femtosecond laser pulses. The light reflected by the reflector 24 and the sample 5 to be measured enters the beam splitter 22 again, and after combining and interfering, it passes through the dichroic mirror 23. The femtosecond laser and the continuous laser are separated by the dichroic mirror 23, wherein the continuous laser enters the optical path compensation module 3, and the femtosecond laser enters the image acquisition module 25. When using a femtosecond laser to measure the surface profile, it is necessary to keep the entire interference optical path stable, then scan the repetition frequency of the femtosecond laser, and at the same time make the image acquisition module 25 continuously record the interference pattern. Since the scanning repetition frequency is equivalent to the scanning femtosecond laser pulse interval, when the optical path difference between the measuring light and the reference light is equal to an integer multiple of the pulse interval, a coherent interference signal can be observed in the image acquisition module 25. For a sample surface with undulating heights, different heights correspond to different optical path differences in the interferometer, so there are also differences in the repetition frequency when coherent interference occurs. The signal processing system 4 converts the repetition frequency of coherent interference of different pixels in the image into an optical path difference, and the two-dimensional point cloud of the optical path difference of all pixels is the surface profile of the object.

[0036] Embodiment 2: Figure 2As shown, the surface profile measurement system for offsetting the environmental noise introduced by the optical path provided by the present embodiment comprises: a light source 1, wherein the light source 1 comprises a femtosecond laser 1-1 and a single-frequency laser 1-2; the light emitted by the femtosecond laser 1-1 enters the dual-wavelength coupler 2 through optical fiber transmission and is divided into two paths: one path passes through a short optical fiber 3 (the short optical fiber refers to the shorter one of the two optical fibers output by the dual-wavelength coupler), and then is directly collimated into a measurement light through a fiber collimator 4; the other path passes through a long optical fiber 5 (the long optical fiber refers to the longer one of the two optical fibers output by the dual-wavelength coupler, and the length difference between the two optical fibers will cause an optical path delay, so that the two lights can cause misalignment interference, and the long optical fiber and the short optical fiber can be interchanged on the premise of ensuring that misalignment interference can occur, which is only an exemplary description here and is not limited), and then is collimated into a reference light through a fiber collimator 6 after delay. Two paths of light with different time delays are transmitted relative to each other in space and enter the beam splitter 7: the measuring light reflected by the beam splitter 7 irradiates the sample through the dichroic mirror 8, and a part of it returns from the sample 13 to be measured passes through the beam splitter 7 and passes through the lens 9, the dichroic mirror 10 and the lens 11 in sequence to enter the image acquisition module 12; the reference light also enters the image acquisition module 12 after being reflected by the beam splitter 7, and interferes with the measuring light. The image acquisition module 12 is used to collect the pattern of interference between the measuring light and the reference light, wherein the lens group composed of the lens 9 and the lens 11 images the surface of the sample 13 to be measured onto the image plane of the image acquisition module 12, thereby constructing a conjugate correspondence between the pixel of the image acquisition module 12 and the spatial position of the sample 13 to be measured.

[0037] In order to achieve active suppression of environmental interference, this embodiment adds a single-frequency laser with a wavelength different from that of the femtosecond laser, which enters the interference optical path together with the femtosecond laser through the dual-wavelength coupler 2. The dichroic mirror 8 of the measuring arm of the interference optical path is used to reflect the single-frequency laser (the femtosecond laser is not affected by it), and the dichroic mirror 10 is used to separate the single-frequency laser from the femtosecond laser after the measuring arm and the reference arm are combined. The single-frequency laser enters the photodetector 14 to obtain its interference signal. Since the coherent scanning of the system is completed in the light source, the entire optical path system should always maintain a steady state during the measurement; in the optical path compensation module, the photodetector 14 only receives the interference signal from the single-frequency laser 1-2, which is not affected by the femtosecond laser scanning, so its signal phase should remain unchanged during the entire measurement process. Environmental noise will change the optical path difference of the interferometer in the form of mechanical vibration or atmospheric refractive index, thus causing the phase of the interferometer to change, and then causing the signal of the photodetector 14 to fluctuate. The interference signal is input to the servo controller 15, and the signal intensity when the interference phase is π / 2 is set as the reference point, so that the length controller 16 can be controlled to stretch the optical fiber to achieve the optical path difference locking of the interference light path. The signal processing system 17 is used to perform pixel-by-pixel time-frequency analysis on the obtained interference pattern of the sample 13 to obtain the contour information of the sample 13 to be tested.

[0038] In a preferred embodiment of the present invention, the repetition frequency of the femtosecond laser 1-1 can be precisely controlled so that the spatial interval of its output pulses L pp The role of the long optical fiber 5 is to make the optical path difference between the two interference arms of the interference module L pp of M times, among which, M is an integer. Thus, when the repetition frequency of the femtosecond laser is scanned, if the optical path difference is exactly equal to ML pp Each pulse in one arm will be M The pulses interfere with each other, and the relative height of the point can be determined based on the repetition frequency at this time.

[0039] Each embodiment in this specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In the description of this specification, the description of reference terms "a preferred embodiment", "further", "specifically", "in the present embodiment", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of this specification. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A surface profile measurement system for offsetting the ambient noise introduced by the optical path, characterized in that: The system includes a light source, an interference optical path, an optical path compensation module and a signal processing system; The light source comprises a first light source and a second light source with different wavelengths, wherein the first light source is used to measure the morphology of the surface of the sample to be measured, and the second light source is used to measure the environmental noise in the interference light path; The interference optical path is used to obtain a pattern of interference between the measuring arm and the reference arm; The optical path compensation module is used to receive the interference phase change of the second light source passing through the interference light path, adjust the optical path difference of the interference light path based on the interference phase change, and generate an optical path difference equivalent to but in the opposite direction of the interference phase change, thereby compensating for the environmental noise generated in the light path; The signal processing system is used to perform pixel-by-pixel time-frequency analysis on the interference pattern of the sample to be tested to obtain the contour of the sample to be tested.

2. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 1, characterized in that: The first light source is a femtosecond laser, and the repetition frequency of the femtosecond laser can be precisely adjusted.

3. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 2, characterized in that: The second light source is a continuous laser, and the continuous laser is a frequency-stable narrow-linewidth laser.

4. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 3, characterized in that: The interference optical path includes a beam combiner, a beam splitter, a dichroic mirror, a reflector and an image acquisition module; The beam combiner is used to combine femtosecond laser and continuous laser of different wavelengths into one beam and send it to the beam splitter; a part of the light emitted by the beam splitter is used as the measuring arm to illuminate the sample to be measured; another part of the light emitted by the beam splitter is emitted to the reflector as the reference arm; the light reflected by the reflector and the sample to be measured enters the beam splitter again for coupling and is sent to the dichroic mirror; the continuous laser emitted by the dichroic mirror is separated and enters the optical path compensation module; the femtosecond laser emitted by the dichroic mirror enters the image acquisition module; the image acquisition module acquires the pattern of interference between the measuring arm and the reference arm.

5. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 4, characterized in that: The optical path compensation module includes a detector, a motion unit and a control unit, wherein the motion unit is connected to the reflector; The detector is used to detect the interference signal of the continuous laser; The control unit controls the reflection mirror to move along the optical axis through the motion unit according to the interference phase fluctuation of the continuous laser light, suppresses the interference phase fluctuation, and thus compensates for the noise generated in the optical path.

6. A surface profile measurement system for offsetting the ambient noise introduced by the optical path, characterized in that: It includes a light source, an interference optical path, an optical path compensation module and a signal processing system; The light source comprises a first light source and a second light source with different wavelengths, the first light source and the second light source are divided into two paths through a dual-wavelength coupler, one path is emitted through a first optical fiber as a measurement light, and the other path is emitted after being delayed by a second optical fiber as a reference light, the two paths of light with different time delays are relatively transmitted in space and enter the interference optical path, wherein the first optical fiber and the second optical fiber have different lengths; The interference optical path is used to obtain a pattern of interference between the measuring arm and the reference arm; The optical path compensation module is used to receive the interference phase change of the second light source passing through the interference optical path, and control the length change of the first optical fiber or the second optical fiber based on the interference phase change to generate an optical path difference equivalent to but in the opposite direction of the interference phase change, thereby compensating for the environmental noise generated in the optical path; The signal processing system is used to perform pixel-by-pixel time-frequency analysis on the interference pattern of the sample to be tested to obtain the contour of the sample to be tested.

7. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 6, characterized in that: The first light source adopts femtosecond laser, and the second light source adopts single-frequency laser.

8. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 7, characterized in that: The function of the second optical fiber is to make the optical path difference between the reference arm and the measuring arm of the interference optical path L pp of M times, among which, L pp is the spatial interval of the femtosecond laser output pulses, M is an integer. When the repetition frequency of the femtosecond laser is scanned, if the optical path difference is exactly equal to ML pp Each pulse in one arm will be M The pulses interfere with each other, and the relative height of the point can be determined based on the repetition frequency at this time.

9. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 7, characterized in that: The optical path compensation module includes a detector, a servo controller and a length controller; The detector is used to detect the interference signal of the single-frequency laser; The servo controller sets the signal intensity when the interference phase is π / 2 as the reference point, and controls the length controller to adjust the length of the first optical fiber or the second optical fiber according to the interference signal of the single-frequency laser to lock the optical path difference of the interference optical path, thereby compensating for the noise generated in the optical path.

10. The surface profile measurement system for canceling the environmental noise introduced by the optical path according to claim 9, characterized in that: The interference module includes a beam splitter, a first dichroic mirror, a first lens, a second dichroic mirror, a second lens and an image acquisition module; The measuring light is reflected by the beam splitter and irradiates the sample to be measured through the first dichroic mirror, and a part of the light returning from the sample to be measured passes through the beam splitter and enters the image acquisition module through the first lens, the second dichroic mirror and the second lens; After being reflected by the beam splitter, the reference light enters the image acquisition module through the first lens, the second dichroic mirror and the second lens to interfere with the measuring light. The image acquisition module collects the pattern of interference between the measuring light and the reference light. The second dichroic mirror is used to separate the single-frequency laser and the femtosecond laser after the measuring arm and the reference arm are combined. The separated single-frequency laser is detected by the detector.

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