Three-dimensional on-line measuring system and method for interference nano surface of synthetic wave
Technical Field
The invention relates to a three-dimensional online measurement system and a three-dimensional online measurement method for a nanometer surface by utilizing light scanning and interference of synthetic waves, in particular to a three-dimensional online measurement system and a three-dimensional online measurement method for a nanometer surface with a boss and deep groove structure, and belongs to the technical field of optical measurement.
Background
[1] Hand, t.a.carolan, j.s.barton, and j.d.c.jones optical bulletin (Optics Letters), 1993, vol 18, no. 16, pages 1361-1363. The working principle of the prior art document [1] is shown in FIG. 1. Light emitted by the semiconductor laser reaches a measuring head after passing through a Faraday isolator and an optical fiber 50: 50 coupler, the measuring head is a Fizeau interferometer, one part of light is reflected by the end face of an optical fiber to be used as reference light, the other part of light is focused by a self-focusing lens and then is projected onto a measured surface, the light is reflected by the measured surface to return to the system again and interferes with the reference light, an interference signal is detected by a detector D1, and the phase of the interference signal is determined by the longitudinal height of a measured point on the measured surface; the driving current of the laser is changed to change the light emitting frequency of the laser, four lights with different frequencies are used for measuring the same point to obtain four interference signals, the phases of the four interference signals are different due to different incident light wave frequencies, the driving current is adjusted to enable the phase difference pi/2 of two adjacent interference signals, and the optical path difference D of the point can be demodulated through the following formula, namely the measurement of the single point is completed:
I n (n =1,2,3,4) is the intensity of the nth interference signal, c is the speed of light, and v is the frequency of incident light. The stepping motor drives the measuring head to transversely scan the measured surface, and the measurement of the measured surface is completed.
[2]DejiaoLin, xiangqianjian jiang, fangXie, weiZhang, linzhangndian bennion, optical express (OpticsExpress), 2004, volume 12, phase 23, pages 5729-5734. Prior art document [2]Before the work ofAs shown in figure 2. Emitted by a semiconductor laser with a wavelength of lambda 0 The light is divided into two paths after passing through the two 3 dB-couplers, one path is reflected by the fiber bragg grating, and the other path is reflected by the reference reflector. The two paths of reflected light meet and interfere again after passing through the 3 dB-coupler, interference signals are reflected by another fiber grating after passing through the gyrator, then pass through the gyrator again and are detected by the PIN detector, signals detected by the detector are processed by the servo circuit and then drive the piezoelectric ceramic tube to adjust the length of a reference arm of the fiber interferometer, and the two interference arms of the stable interferometer are always in an orthogonal state (the phase difference is pi/2), so that the purpose of stabilizing the interferometer is achieved.
Wavelength lambda emitted by a tunable laser m The variable light is divided into two paths after passing through the two optical fiber 3 dB-couplers, one path of light passes through the optical fiber auto-collimation lens and then is reflected by the measuring mirror to return to the interferometer again, the other path of light passes through the optical fiber auto-collimation lens and then is reflected by the reference mirror to return to the interferometer again, the two paths of light meet after passing through the 3 dB-coupler to form an interference signal, the interference signal passes through the gyrator and the optical fiber grating and then is detected by the PIN detector, and the displacement of the measuring mirror is measured through phase analysis.
The problems and disadvantages of the two prior arts are:
1. the point scanning measurement mode is adopted, the measurement speed is low, two-dimensional scanning is required for surface three-dimensional measurement, the scanning mechanism is complex, and the instrument cost is high;
2. the sensor is sensitive to the interference of measuring environmental vibration and temperature drift and is not suitable for online measurement;
3. the measuring range is limited by the wavelength lambda of incident light waves, the measuring range is less than lambda/2, and the nano surface with the boss and deep groove structure cannot be measured.
The invention aims to provide a system and a method for three-dimensional online measurement of a synthetic wave interference nano surface by utilizing light scanning, aiming at the problems and the defects in the prior art.
Disclosure of Invention
The purpose of the invention is realized by the following technical scheme.
The system is composed of a super-radiation light-emitting diode (SLD), an optical fiber auto-collimation lens Z, a double-period grating G, a collimation lens L1, a spectroscope BS, a flat column focusing lens L2 with a plane plated with a semi-transparent and semi-reflective film, a longitudinal micro-motion workbench M1, a transverse micro-motion workbench M2, a high-speed linear array CCD, a phase measurement, a signal generator, an A/D conversion card, a computer, a result output and drive control; a common-path interferometer is formed by a super-radiation light-emitting diode SLD with the center wavelength of 850nm and the spectral width of 40nm, an optical fiber auto-collimation lens Z, a double-period grating G, a spectroscope BS and a flat column focusing lens L2 with a plane plated with a semi-transparent semi-reflective film, so that the influence of environmental vibration and temperature drift on a measuring system is subjected to common-mode suppression, and the measuring system is suitable for online measurement; the light with the spectral width of 40nm emitted by the super-radiation light-emitting diode SLD is collimated into parallel light beams after passing through the optical fiber auto-collimation lens Z, the light beams are dispersed into two fan-shaped light sheets with the wavelengths continuously and uniformly distributed in space by the double-period grating G, the two fan-shaped light sheets are collimated into two parallel light sheets which are transversely staggered and partially overlapped, the two parallel light sheets form a parallel light sheet consisting of a series of parallel synthetic waves at the spatially overlapped part, the synthetic wave parallel light sheet vertically enters the plano-cylindrical lens focusing L2 after penetrating through the spectroscope BS, the plane of the plano-cylindrical focusing lens L2 is plated with a semi-transparent semi-reflective film, half of the light intensity of the synthetic wave parallel light sheet is reflected and returns along the original path, and the partial light is used as reference light; the other half of the light intensity is transmitted and focused into a light ray with the width less than 1 μm, the light ray scans the measured surface, the light ray is reflected back to the system by the measured surface to meet and interfere with the reference light, the synthesized wave interference signal is reflected by the spectroscope BS and then detected by the high-speed linear array CCD, different pixels of the CCD detect the interference signal generated by the meeting of the light reflected back by different measured points on the measured surface and the reference light, and the longitudinal (vertical to the measured surface) information of the measured surface is loaded in the phase change of the interference signal. The phase variation of each pixel interference signal of the CCD is demodulated, namely the longitudinal variation of a corresponding measured point on the measured surface is measured, and the surface two-dimensional measurement is realized; the transverse micro-motion workbench M2 drives the tested device to transversely move, light rays scan the tested surface, and interference signals detected by each pixel of the CCD are processed in the same way, so that three-dimensional measurement of the surface is realized.
In order to demodulate the phase variation of the interference signal, a signal generator sends out periodic sawtooth wave voltage with certain amplitude, and the sawtooth wave voltage drives a longitudinal micro-motion workbench M1 to adjust the optical path of a measuring optical path through drive control; if the measured surface is a surface with a boss and deep groove structure and longitudinal change of delta h exists, the phase difference between the interference signal and the sawtooth wave signal is
Comparing the phase of interference signal with the phase of sawtooth wave signal, measuring its phase difference delta 58388in the phase measuring link, analog-to-digital converting by A/D converting card, and data processing by computer to measure the longitudinal change value delta h of the corresponding measured point, and processing the interference signal output by each pixel of CCD array to complete the two-dimensional measurement of the measured surface; driving and controlling the transverse worktable M2 to transversely move, transversely scanning the surface to be measured by light rays, and uniformly processing signals output by each pixel of the linear array CCD one by one to finish the three-dimensional measurement of the surface to be measured; measuring range is lambda
s /2, synthetic wavelength
Much larger than the wavelength lambda of light wave
1 And λ
2 The overlapped two light wave wavelengths lambda can be adjusted by adjusting the size of two periods of the grating
1 And λ
2 Of such a size thatThe measurement range is adjusted by obtaining the synthetic wavelengths with different sizes, so that the system is suitable for the three-dimensional online measurement of the nano surface with a boss and deep groove structure.
The beneficial effects of the invention are:
1. and scanning the nano surface with light to perform three-dimensional measurement. Scanning a parallel light sheet consisting of a series of parallel synthetic waves to perform line scanning measurement on the measured surface, and positioning once in the measurement process to finish surface two-dimensional measurement; and (5) transversely scanning the surface to be measured by light rays to finish the three-dimensional measurement of the surface. The invention has the advantages of high measuring speed, simple scanning mechanism, low system cost and high measuring precision.
2. The invention uses the light source, the optical fiber auto-collimation lens Z, the double period grating G, the collimation lens L1, the spectroscope BS and the flat column focusing lens L2 to form a common-path interference system, so that the influence of the interference such as environmental vibration, temperature drift and the like on the measurement system is suppressed in a common mode, and the system is suitable for online measurement.
3. The measuring range of the interference is enlarged by using a method of interference of the synthetic wave. Measuring range is lambda
s /2, synthetic wavelength
Much larger than the wavelength lambda of light wave
1 And λ
2 And can be adjusted by adjusting the wavelength λ of light wave
1 And λ
2 Different synthetic wavelengths are obtained to adjust the measuring range, the measuring range can reach 600-1000 mu m, and the resolution ratio is superior to 5nm, so that the system is suitable for the three-dimensional online measurement of the nanometer surface with a boss and deep groove structure.
Drawings
FIG. 1 is a schematic diagram of the operation of prior art document [1 ];
FIG. 2 is a schematic diagram of the operation of prior art document [2 ];
fig. 3 is a working principle diagram of the present invention.
The figure is marked with: the device comprises a Z-optical fiber auto-collimation lens, a G-double period grating, an L1-collimation lens, a BS-spectroscope, an L2-plano-cylindrical focusing lens, an M1-longitudinal micro-motion workbench and an M2-transverse micro-motion workbench.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
As shown in fig. 3, light with a spectral width of 40nm emitted by a superluminescent diode SLD with a central wavelength of 850nm passes through an optical fiber auto-collimating lens Z and is collimated into a parallel light beam, the parallel light beam is dispersed by a bi-periodic grating G into two sectorial light sheets with wavelengths continuously and uniformly distributed in space, the two sectorial light sheets are collimated into parallel light sheets with wavelengths continuously and uniformly distributed in space by a collimating lens L1, and the two parallel light sheets are parallel to each other, laterally staggered, and partially overlapped in space. Wavelength lambda of two parallel light sheets corresponding to different points in the transverse direction of the overlapping portion of the two parallel light sheets
1 And λ
2 In contrast, the two different wavelengths meet to form a compositeWave, synthetic wavelength of synthetic wave
Much larger than the wavelength lambda of light wave
1 And λ
2 . The parallel light sheet of the synthetic wave penetrates through the spectroscope BS and vertically enters the plano-cylindrical focusing lens L2, the plane of the plano-cylindrical focusing lens L2 is plated with a semi-transparent and semi-reflective film, half of the light intensity of the parallel light sheet of the synthetic wave is reflected and returns along the original path, and the part of light is used as reference light; the other half of the light intensity is transmitted and focused into a light ray with the width less than 1 μm, the light ray is projected to the surface of the tested device and reflected back to the system by the tested surface, and meets and interferes with the reference light, and the synthesized wave interference signal is reflected by the spectroscope BS and detected by the high-speed linear array CCD. The interference signals of the reflected light of different measured points on the measured surface are detected by different pixels of the linear array CCD, the phase variation delta \58388ofthe interference signals, and the longitudinal variation value delta h of the measured points is embodied. Delta 58388 and delta h have a relationship

Synthetic wavelength lambda
s Much larger than the wavelength of the light, which is determined by the two grating periods of the bi-periodic grating G. The measuring range of the system is lambda
s And/2, which is much larger than the traditional interferometric measuring range lambda/2 (lambda is the wavelength of light wave). The purpose of wide-range interference measurement is realized, and the system is suitable for three-dimensional measurement of the nanometer surface with a boss structure and a deep groove structure.
In order to demodulate the phase variation of the interference signal, the sawtooth wave signal sent by the signal generator drives the longitudinal micro-motion workbench M1 to longitudinally scan at a constant speed through driving control so as to realize the adjustment of the optical path length of the measuring optical path. The initial position of the worktable and the amplitude of the sawtooth wave signal are adjusted, so that the sawtooth wave signal and an interference signal of a certain pixel of the CCD change in the same frequency and the same phase in the optical path scanning process. If the measured surface is an ideal plane, interference signals of other pixels of the CCD are also in the same frequency and the same phase as the sawtooth wave signals; if the measured surface is a surface with a boss and deep groove structure, the phases of interference signals of other pixels of the CCD and sawtooth wave signals are different, and the phase difference delta 58388between the interference signals and the sawtooth wave signals is measured by phase measurement; the interference signal of each pixel of the CCD is processed in such a way that the two-dimensional measurement of the measured surface is completed; the driving control drives the transverse micro-motion workbench M2 to transversely move, the light rays scan the surface to be measured, and then the interference signals of each pixel of the CCD are processed, so that the three-dimensional measurement of the surface is completed.
The specific examples described above are described to illustrate implementations of the invention. Other variations and modifications of the invention will be apparent to those skilled in the art, and it is intended that any modifications/variations or equivalent arrangements which fall within the spirit and scope of the invention disclosed and the basic underlying principles thereof fall within the scope of the invention claimed.