Non-contact measuring head device for nanometer coordinate measuring machine and measuring method

Abstract

The invention discloses a non-contact measuring head device and a measuring method for a nanometer coordinate measuring machine, and the measuring head device comprises a laser holographic measuring module, an optical microscopic imaging module and a signal processing module. The laser holographic measurement module comprises a semiconductor laser, a straight stripe grating close to the semiconductor laser, a holographic grating far away from the semiconductor laser, a first photoelectric detector, a second photoelectric detector, a first lens, a second lens, a first spectroscope and a microscope objective, wherein the first photoelectric detector and the second photoelectric detector are located on the left side and the right side of the semiconductor laser respectively. The signal processing module calculates out-of-focus error signals according to the electric signals obtained by the laser holography measurement module, calculates out-of-focus amount of each measurement point on the surface of the sample according to the linear relation between the out-of-focus amount of the surface of the measured sample leaving the focal plane of the microscope objective and the out-of-focus error signals, and calculates out-of-focus amount of each measurement point on the surface of the sample according to coordinate values of the nanometer coordinate measurement machine. And obtaining the coordinate value of each measuring point on the surface of the sample. According to the invention, the aiming resolution can be improved, and high-precision and high-resolution three-dimensional measurement is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of precision measurement, and particularly relates to a non-contact probe device for a nanometer coordinate measuring machine and a measuring method. BACKGROUND

[0002] With the rapid development of ultra-precision machining technology and the wide application of micro-nano structures in many fields, the demand for high-precision measurement at the nanometer level is increasing. As a key device for realizing high-precision measurement, the performance of the probe, the core component of the nanometer coordinate measuring machine, directly affects the accuracy and efficiency of the measurement.

[0003] The traditional contact probe is easy to cause damage to the surface of the sample when measuring the micrometer level, especially the nanometer level of soft or brittle sample to be measured, resulting in inaccurate measurement results or even damage to the sample. Although the existing non-contact measurement methods such as laser triangulation method have fast measurement speed, the resolution can only reach 1 μm, which is difficult to meet the demand of nanometer level measurement; the phase shift technology method has high longitudinal accuracy, but the transverse resolution can only reach micrometer level; the laser automatic focusing method has a resolution of nanometer level within 10 μm, but is only suitable for one-dimensional measurement; the white light interference measurement technology can reconstruct the three-dimensional profile of the object, but cannot achieve nanometer resolution and has a large volume; the confocal microscopic measurement technology has a longitudinal resolution of 0.5 μm and a transverse resolution of 1 μm; the holographic measurement technology can quickly reconstruct the image of the object and measure in real time, but the accuracy is only micrometer level.

[0004] Therefore, the current measurement technology has deficiencies in aiming resolution, and it is difficult to realize high-precision, high-resolution three-dimensional measurement of nanometer level samples. In nanometer level measurement, small aiming errors can cause large deviations in measurement results, which cannot meet the current demand for accurate measurement of micro-nano structures at the nanometer level. SUMMARY

[0005] The purpose of the present application is to provide a non-contact probe device for a nanometer coordinate measuring machine and a measuring method, which can improve the aiming resolution and realize high-precision, high-resolution three-dimensional measurement.

[0006] In order to achieve the above-mentioned purpose, one aspect of the present application provides a non-contact probe device for a nanometer coordinate measuring machine, comprising a laser holographic measurement module, an optical microscopic imaging module and a signal processing module, The laser holographic measurement module comprises a semiconductor laser, a straight stripe grating close to the semiconductor laser and a holographic grating far from the semiconductor laser, a first photodetector and a second photodetector respectively located on the left and right sides of the semiconductor laser, a first lens, a second lens, a first beam splitter and a microscopic objective lens; The light beam emitted by the semiconductor laser passes through the straight stripe grating and the 0th order diffracted light enters the first lens to become a parallel light beam, is reflected by the first beam splitter, and is converged on the surface of the measured sample through the microscope objective lens; the light beam reflected from the surface of the measured sample reversely passes through the microscope objective lens, is reflected by the first beam splitter, passes through the second lens, reaches the holographic grating, and is divided into two light beams, which are received by the first photodetector and the second photodetector respectively, and the optical signals are converted into the first electric signal and the second electric signal respectively; The signal processing module calculates the defocusing error signal according to the first electric signal and the second electric signal, calculates the defocusing amount of each measurement point on the surface of the sample by using the linear relationship between the defocusing amount of the surface of the measured sample from the focal plane of the microscope objective lens and the defocusing error signal, and obtains the coordinate value of each measurement point on the surface of the sample in combination with the coordinate value of the sample measured by the nanometer coordinate measuring machine. The optical microscopic imaging module is used for observing the positioning condition of the sample and the measurement condition of the surface of the sample.

[0007] Another aspect of the present application provides a non-contact measurement method for a nanometer coordinate measuring machine, which uses the probe device described above to perform non-contact measurement, and the method comprises the following steps: Step S1, calibrating the linear relationship between the defocusing amount and the defocusing error signal; Step S2, installing the probe device on the nanometer coordinate measuring machine, and adjusting the optical microscopic imaging module so that the optical microscopic imaging module can clearly display the surface topography of the measured sample; Step S3, placing the measured sample on the worktable of the nanometer coordinate measuring machine, coarsely adjusting the nanometer coordinate measuring machine, moving the sample into the measurement range of the probe device, observing the sample through the optical microscopic imaging module, finely adjusting the nanometer coordinate measuring machine so that the target measurement region of the measured sample is located at the center of the field of view of the microscope objective lens, and the entire field of view is clearly imaged; Step S4, slowly moving the measured sample in the three-dimensional space, calculating the defocusing error signal of the probe device in real time during the movement, when the focusing error signal is zero, it indicates that the surface of the measured sample is on the focal plane of the microscope objective lens at this time, recording the coordinate value of the nanometer coordinate measuring machine at this time as the height reference point of the measurement, continuing to move the sample horizontally, changing the focusing error signal, calculating the defocusing amount of each measurement point on the surface of the sample as the height variation relative to the height reference point in combination with the calibrated corresponding relationship between the defocusing amount and the defocusing error signal, and calculating the coordinate value of each measurement point on the surface of the sample in combination with the horizontal coordinate value measured by the nanometer coordinate measuring machine.

[0008] The non-contact probe device and the measurement method for the nanometer coordinate measuring machine according to the above aspects of the present application can improve the aiming resolution and realize high-precision and high-resolution three-dimensional measurement. BRIEF DESCRIPTION OF DRAWINGS

[0009] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort: Figure 1 This is a schematic diagram of a non-contact probe device for a nano-coordinate measuring machine according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a laser holographic unit according to an embodiment of the present invention; Figure 3 This is a schematic diagram showing the sample under test at different positions on the focal plane of a microscope objective, according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the structure of a nano-coordinate measuring machine according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of a nano-coordinate measuring machine length measuring device according to an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the relationship between the defocus amount and the defocus error signal according to an embodiment of the present invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0011] One embodiment of the present invention provides a non-contact probe device for a nanometer coordinate measuring machine, such as... Figure 1 As shown, the non-contact probe device of this embodiment includes a laser holographic measurement module, an optical microscopic imaging module, and a signal processing module. The laser holographic measurement module includes a laser holographic unit 11, a first lens 12, a first beam splitter 13, and a microscope objective 14. The optical microscopic imaging module includes a light source 21, a second beam splitter 23, a third lens 24, and a CCD camera 25. The signal processing module includes a signal acquisition unit 31 and a computer 32.

[0012] The laser holographic unit 11 includes a semiconductor laser 111, a holographic optical element 113, and a photodetector. The holographic optical element 113 includes a straight-striped grating 113a close to the semiconductor laser 111 and a holographic grating 113b further away from the semiconductor laser 111. The holographic grating 113b is a Fresnel diffraction region.

[0013] The photodetector is divided into two groups: the first photodetector 112a and the second photodetector 112b, which are located on the left and right sides of the semiconductor laser 111, respectively. The two groups of detectors contain three photodetectors, S1, S2, S3 and S4, S5, S6, respectively.

[0014] like Figure 2 As shown, the light beam emitted by the semiconductor laser 111 passes through the straight-striped grating 113. After diffraction, the 0th-order diffracted light enters the first lens 12 and becomes a parallel beam. This beam is reflected by the first beam splitter 13 and then converged onto the surface of the sample 15 under test by the microscope objective 14. The beam reflected back from the surface of the sample 15 passes back through the microscope objective 14. A small portion of the light passes through the first beam splitter 13 and enters the optical microscopic imaging module, while most of the light is reflected by the first beam splitter 13 and passes through the second lens 12. After reaching the holographic grating 113b, it is split into two beams, which are received by the first photodetector 112a and the second photodetector 112b, respectively, and the optical signal is converted into an electrical signal.

[0015] The size of the light spot area received by the first photodetector 112a and the second photodetector 112b is related to the position of the sample 15 under test relative to the focal plane of the microscope objective 14. For example... Figure 3 As shown, when the sample 15 under test is at the focal plane of the focusing lens, i.e., in the focused state, the light spot areas received by the first photodetector 112a and the second photodetector 112b are equal, and the output voltage magnitudes are the same. When the sample 15 under test is outside the focal plane of the microscope objective 14, it is called the far-focus state, at which time the light spot area on the first photodetector 112a is larger than the light spot area on the second photodetector 112b. When the sample 15 under test is within the focal plane of the microscope objective 14, it is called the near-focus state, at which time the light spot area on the first photodetector 112a is smaller than the light spot area on the second photodetector 112b. When the surface of the sample 15 under test is not at the focal plane of the microscope objective 14, it is collectively referred to as the defocus state. In the defocus state, the light spot sizes received by the first photodetector 112a and the second photodetector 112b are different, and the output voltage signal magnitudes are different, generating a defocus error signal U. fe =(U s1 +U s3 +U s5 )-(U s2 +U s4 +U s6 ), where U s1 U s2 U s3 U s4 U s5 U s6S1, S2, S3, S4, S5, and S6 represent the voltage values ​​generated on the corresponding detector blocks of the first photodetector 112a and the second photodetector 112b, respectively. The defocus amount and the defocus error signal are linearly related within a certain range.

[0016] The electrical signal output by the photodetector is acquired by the signal acquisition unit 31 and transmitted to the computer 32. The computer 32 performs calculations and processing using the algorithm set in the computer 32, and obtains the longitudinal height value of the surface of the sample 15 under test using a linear relationship. The measurement resolution of the longitudinal height value is at the nanometer level.

[0017] The light emitted by the light source 21 is collimated by the second lens 22, and after passing through the second beam splitter 23 and the first beam splitter 13, it is focused by the microscope objective 14 onto the surface of the sample 15 under test. The light beam reflected from the surface of the sample 15 under test passes back through the microscope objective 14, and a small portion of the light from the laser holographic unit 11 passes through the first beam splitter 13, the second beam splitter 23 and the third lens 24, and is imaged on the receiving surface of the CCD camera 25.

[0018] In one embodiment, the semiconductor laser 11 emits visible light in the blue light band, particularly with a wavelength less than 450 nm, to improve resolution. The microscope objective 14 features high magnification, high numerical aperture, and a long working distance, simultaneously satisfying 50× magnification and a numerical aperture greater than or equal to 0.65 to further improve resolution, achieving a spatial resolution of 0.1 nm. Furthermore, the microscope objective 14 is a long working distance microscope objective, with a working distance greater than or equal to 7 mm, to improve measurement safety and reduce or even eliminate the possibility of collision between the sample 15 and the probe.

[0019] The light source 21 uses an optical fiber to transmit the illumination beam into the microscopic imaging system to reduce thermal interference. The morphology of the surface of the sample 15 under test is observed through the CCD camera 25, while the focusing of the beam from the laser holographic unit 11 on the surface of the sample 15 is also observed.

[0020] Nanoscale coordinate measuring machine 2 Figure 4 As shown, it consists of a three-dimensional motion device 201, length measuring devices 202 and 204, and a vibration isolation platform 205. The three-dimensional motion device 201 drives the sample under test to achieve high-precision movement in the X, Y, and Z directions in space. The length measuring devices 202 and 204 measure the displacement in the X, Y, and Z directions in space. The base 206 is used to install and support the three-dimensional motion device 201, the length measuring devices 202 and 204, and the non-contact probe device 1.

[0021] Preferably, the X and Y axes of the three-dimensional motion device 201 can achieve movement within a range of 0 to 50 mm, with a positioning accuracy better than 0.1 μm and a Z-axis resolution better than 1 nm.

[0022] Preferably, the length measuring device is as follows: Figure 5As shown, this is a three-dimensional laser interferometry instrument, which includes laser interferometers 202a, 202b, and 202c distributed in the X, Y, and Z directions of space, as well as a roof corner reflector 207.

[0023] Embodiments of the present invention also provide a non-contact measurement method for a nanometer coordinate measuring machine, which utilizes the probe device of the above embodiments of the present invention for non-contact measurement. The method includes: Step S1: Probe device calibration. Using metrological standards and a linear Z-axis micro-displacement platform with sub-nanometer displacement resolution, repeatability positioning error better than 1 nm, and maximum displacement greater than 15 μm, the linear relationship between the defocus amount and the defocus error signal is calibrated. Figure 6 As shown, in ΔZ min To ΔZ max Defocus amount ΔZ and defocus error signal U within the range fe The linear relationship is ΔZ=a * U fe , where a is the linear coefficient.

[0024] Step S2: Measurement preparation. Install the non-contact probe device on the nano-coordinate measuring machine 16, and adjust the intensity of the light source 21 and the parameters of the CCD camera 25 so that the optical microscopic imaging module can clearly display the surface morphology of the sample 15 being measured.

[0025] Step S3: Sample positioning. Place the sample 15 to be tested on the stage of the nanocoordinate measuring machine 16. Coarsely adjust the nanocoordinate measuring machine 16 to move the sample 15 into the measurement range of the probe device. Then, observe the sample 15 through the optical microscopic imaging module. Finely adjust the nanocoordinate measuring machine 16 until the target measurement area of ​​the sample 15 is located at the center of the field of view of the microscope objective, and the entire field of view is clearly imaged.

[0026] Step S4: Measurement process. The three-dimensional motion device 201 moves the sample 15 under test slowly in three-dimensional space. During the movement, the defocus error signal of the probe device is calculated in real time. When the defocus error signal U... fe When the value is zero, it indicates that the surface of the sample 15 being measured is on the focal plane of the microscope objective. The coordinate values ​​(X0, Y0, Z0) of the nano-coordinate measuring machine 16 at this point are recorded as the height reference point for measurement; at this time, ΔZ = 0. The sample 15 is moved horizontally further, and the defocusing error signal U of the probe device is recorded. fe The change occurs, and the corresponding relationship between the defocus amount calibrated in step one and the defocus error signal ΔZ=a is considered. * U fe The defocusing amount ΔZ at each measurement point on sample 15 was calculated. i As a measure of height change relative to the height reference point, the coordinate values ​​(X) measured by the nano-coordinate measuring machine 16 are used. i Yi Z0), to obtain the coordinate values ​​(X, Z0) of each measurement point on the surface of sample 15. i Y i Z0+ΔZ i ).

[0027] The coordinate values ​​of the nanocoordinate machine are obtained by laser interferometry in the X, Y, and Z directions. During measurement preparation and sample positioning, a high-resolution optical microscopic imaging module enables more precise sample positioning, reducing the impact of sample position deviation on aiming resolution. During the measurement process, a CCD camera 25 monitors the sample surface in real time, ensuring the accuracy and integrity of the measurement process.

[0028] In summary, this invention provides a high-precision, high-resolution, simple-structure, and low-cost fixed-focus microscopic probe device based on holographic laser technology. It solves the problems of existing technologies, such as difficulty in achieving nanometer-level measurement accuracy, high requirements for the measured object, complex optical path, and high measurement cost. This invention, applied to a nanometer coordinate measuring machine, possesses nanometer resolution, enabling rapid aiming and high-precision nanometer-level measurement of the measured sample.

[0029] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A non-contact probe device for a nanometer coordinate measuring machine, characterized in that, It includes a laser holographic measurement module, an optical microscopic imaging module, and a signal processing module. The laser holographic measurement module includes a semiconductor laser, a straight stripe grating close to the semiconductor laser and a holographic grating far from the semiconductor laser, a first photodetector and a second photodetector located on the left and right sides of the semiconductor laser, a first lens, a second lens, a first beam splitter, and a microscope objective. The light beam emitted by the semiconductor laser is diffracted by a straight-striped grating. The 0th-order diffracted light enters the first lens and becomes a parallel beam. After being reflected by the first beam splitter, it is focused onto the surface of the sample under test by the microscope objective. The beam reflected back from the surface of the sample under test passes through the microscope objective in the opposite direction. It is reflected by the first beam splitter and passes through the second lens. After reaching the holographic grating, it is split into two beams, which are received by the first photodetector and the second photodetector, respectively. The optical signals are converted into the first electrical signal and the second electrical signal, respectively. The signal processing module calculates the defocus error signal based on the first and second electrical signals. It uses the linear relationship between the amount of defocus of the sample surface away from the focal plane of the microscope objective and the defocus error signal to calculate the amount of defocus at each measurement point on the sample surface. Combined with the coordinate values ​​of the sample measured by the nano-coordinate measuring machine, the coordinate values ​​of each measurement point on the sample surface are obtained. The optical microscopy imaging module is used to observe the positioning of the sample and measure the sample surface.

2. The non-contact probe device for a nano-coordinate measuring machine according to claim 1, characterized in that, The first and second photodetectors each consist of three photodetectors; Defocus error signal U fe =(U s1 +U s3 +U s5 )-(U s2 +U s4 +U s6 ), where U s1 U s2 U s3 U s4 U s5 U s6 These represent the voltage values ​​generated on the corresponding photodetectors of the first and second photodetectors, respectively.

3. The non-contact probe device for a nanometer coordinate measuring machine according to claim 1 or 2, characterized in that, The optical microscopic imaging module includes a light source, a second beam splitter, a third lens, and a CCD camera; The light emitted from the light source is collimated by the second lens, and after passing through the second beam splitter and the first beam splitter, it is focused onto the surface of the sample under test by the microscope objective. The light beam reflected back from the surface of the sample under test passes back through the microscope objective, and then through the first beam splitter, the second beam splitter and the third lens, and is imaged on the receiving surface of the CCD camera.

4. The non-contact probe device for a nano-coordinate measuring machine according to claim 1 or 2, characterized in that, The signal processing module includes a signal acquisition unit and a computer. The signal acquisition unit acquires a first electrical signal and a second electrical signal and transmits them to the computer. The computer calculates the coordinate values ​​of each measurement point on the sample surface based on the first electrical signal and the second electrical signal.

5. The non-contact probe device for a nano-coordinate measuring machine according to claim 1 or 2, characterized in that, Semiconductor lasers emit visible light in the blue light band, with a wavelength less than 450nm.

6. The non-contact probe device for a nano-coordinate measuring machine according to claim 1 or 2, characterized in that, The microscope objective has a magnification of 50x, a numerical aperture of ≥0.65, and a working distance of ≥7mm.

7. A non-contact measurement method for a nanometer coordinate measuring machine, characterized in that, The method for performing non-contact measurement using the probe device according to any one of claims 1-6 includes: Step S1: Calibrate the linear relationship between the defocus amount and the defocus error signal; Step S2: Install the probe device on the nano-coordinate measuring machine and adjust the optical microscopy imaging module so that the optical microscopy imaging module can clearly display the surface morphology of the sample being tested. Step S3: Place the sample to be tested on the stage of the nano-coordinate measuring machine, coarsely adjust the nano-coordinate measuring machine, move the sample into the measurement range of the probe device, observe the sample through the optical microscopic imaging module, and finely adjust the nano-coordinate measuring machine until the target measurement area of ​​the sample is located at the center of the field of view of the microscope objective lens, and the entire field of view is clearly imaged. Step S4: Slowly move the sample under test in three-dimensional space. During the movement, calculate the defocus error signal of the probe device in real time. When the focus error signal is zero, it indicates that the surface of the sample under test is on the focal plane of the microscope objective. Record the coordinate value of the nano-coordinate measuring machine at this time as the height reference point for measurement. Continue to move the sample horizontally to change the focus error signal. Combine the correspondence between the calibrated defocus amount and the defocus error signal to calculate the defocus amount of each measurement point on the sample surface as the height change relative to the height reference point. Combine the horizontal coordinate value measured by the nano-coordinate measuring machine to calculate the coordinate value of each measurement point on the sample surface.

8. The non-contact measurement method according to claim 7, characterized in that, In step S1, the linear relationship between the defocus amount and the defocus error signal is calibrated using metrological standard instruments and a linear Z-axis micro-displacement platform with a displacement resolution of sub-nanometer, a repeatability positioning error better than 1nm, and a maximum displacement greater than 15μm.

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