CN112254658B - Method for tracing magnitude of film thickness - Google Patents
Method for tracing magnitude of film thickness Download PDFInfo
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- CN112254658B CN112254658B CN202011042508.XA CN202011042508A CN112254658B CN 112254658 B CN112254658 B CN 112254658B CN 202011042508 A CN202011042508 A CN 202011042508A CN 112254658 B CN112254658 B CN 112254658B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
- G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
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Abstract
The invention provides a method for tracing the source of a film thickness magnitude, which solves the problem that the tracing chain length of the existing magnitude tracing system can not be directly traced to the national length measurement standard. The value of the film thickness can be traced to the optical path between the wide spectrum light interference signal peaks, the optical path between the wide spectrum light interference signal peaks can be traced to the optical path scanning amount of the optical path scanning device, the optical path scanning amount of the optical delay line can be traced to the wavelength and relative frequency stability of the output light signal of the frequency stabilized laser, and the wavelength and relative frequency stability of the output light signal of the frequency stabilized laser can be traced to the reference frequency stabilized laser in the national length measurement standard, so that a complete tracing system is formed, and the tracing chain is short and simple without the help of intermediate tracing conversion parameters.
Description
Technical Field
The invention relates to the technical field of optical test and measurement, in particular to a magnitude traceability method of film thickness.
Background
With the vigorous development of material science and technology, in order to meet the urgent needs in the fields of microelectronics, optoelectronics, new energy and the like, thin film materials are widely applied in the fields of optical engineering, mechanical engineering, communication engineering, bioengineering, aerospace engineering, chemical engineering, medical engineering and the like. The thickness of the film is not only one of the key parameters in the production of the film, but also determines the application performance of the film in the scenes of mechanics, electromagnetism, photoelectricity, optics and the like. Accurate measurement of film thickness has been the focus of research in the related art as described above. Meanwhile, the traceability of the film thickness measurement result is one of the important ways for evaluating the correctness of the measurement result of the film thickness measurement method.
The ultrasonic film thickness gauge calibration standard (JJF1126-2004) passed by China in 2004 provides an effective traceability way for the ultrasonic film thickness gauge, and the calibration standard is only suitable for the ultrasonic film thickness gauge with the measuring range larger than 0.5 mm; the calibration specification of rubber and plastic film thickness gauges (JJF1488-2014) passed in 2014 provides a basis for tracing the rubber and plastic film thickness gauges by mechanical measurement methods, but has strict limitation on the types of films and cannot cover the tracing requirement of the thickness values of most types of films; the point solution (coulomb) thickness meter calibration standard (JJF 1707) 2018 passed in 2018 also has strict limitation on the types of films to be measured, and is only suitable for value traceability of an electrolytic metal coating thickness meter. The calibration standard can realize the tracing for the thickness value of the measured film, but is only suitable for the tracing of the value of the specific kind of film.
In 2014, the physical science of the Ministry of construction and Gacisian of Ministry of Japan discloses a nanometer film thickness measurement and magnitude traceability research based on an X-ray grazing method (2014,63(006):109-, the method for tracing the thickness value of the nano film which can be traced to the lattice spacing and the angle measurement standard of the monocrystalline silicon yard is provided while realizing the high-precision measurement of the thickness of the nano film, the thickness value of the nano film is traced to the atomic lattice spacing of the monocrystalline silicon which stably exists in the nature, the tracing of the geometrical quantity of the nano scale is realized, the process detection requirement of the information industry is met, but the magnitude tracing method firstly traces the wavelength of the copper target X-ray identification spectrum to the atomic lattice constant of the monocrystalline silicon, and then, the tracing of the thickness value of the nano film is realized by means of the lattice parameters of the atomic lattices, the tracing chain is long, and the source cannot be directly traced to the national length measurement standard.
Disclosure of Invention
In order to solve the problem that the source tracing chain length of the existing film thickness source tracing system cannot directly trace the source value national length measurement standard, the invention provides a film thickness source tracing method, which traces the measured value of the film thickness to the national length measurement standard and ensures the accuracy of the measurement result and the consistency of the measurement unit.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
a method for tracing the magnitude of a film thickness is used for tracing the magnitude of the film thickness measured by a common-path self-calibration film thickness measuring device, the common-path self-calibration film thickness measuring device comprises a light source output module, a beam splitting coupler, a first measuring interferometer coupler, a film thickness measuring probe module, a second measuring interferometer coupler, an interference and demodulation module and a collection and control module, and an optical path scanning device is arranged in the interference and demodulation module; the light source output module comprises a wide-spectrum light source and a frequency stabilized laser, output light of the wide-spectrum light source and the frequency stabilized laser (103) is divided into two paths through a beam splitting coupler, enters the film thickness measuring probe module through a first measuring interferometer coupler and a second measuring interferometer coupler respectively for parameter measurement, return light measured by the film thickness measuring probe module enters an optical path scanning device of the interference and demodulation module through the first measuring interferometer coupler and the second measuring interferometer coupler respectively for scanning optical path matching to obtain a frequency stabilized laser interference signal and a wide-spectrum light interference signal, and the frequency stabilized laser interference signal and the wide-spectrum light interference signal are transmitted to the acquisition and control module;
the tracing method at least comprises the following steps:
s11, the thickness of the film to be measured can be traced upwards to the optical path difference between different wide-spectrum light interference signal peaks;
s12, the optical path between the interference signal peaks of the broad spectrum light can be traced upwards to the optical path scanning amount of the optical path scanning device;
s13, the optical path scanning quantity of the optical path scanning device can be traced upwards to the wavelength and relative frequency stability of the output light of the frequency stabilized laser (103) of the working metering standard device;
s14, the wavelength and the relative frequency stability of output light of the frequency stabilized laser of the working measurement standard device can be traced upwards to a reference frequency stabilized laser A in a national length measurement standard device; the calibration of the wavelength and the relative frequency stability of the output optical signal of the frequency stabilized laser is synchronously completed, and the wavelength and the relative frequency stability of the output optical signal of the frequency stabilized laser are synchronously calibrated through a reference frequency stabilized laser A in a national length standard device, so that the wavelength and the relative frequency stability are directly linked with the definition of a length basic unit of 'meter' in the international basic unit system, and the stability and the certainty of a tracing result are ensured.
Preferably, the metering performance of the reference frequency-stabilized laser A in the national length standard device in the step S14 is 3-10 times that of the frequency-stabilized laser in the common-path self-calibration film thickness measuring device.
Preferably, according to the above method for tracing the film thickness value, the value transmission process of the frequency stabilized laser a in the national length measurement reference instrument is as follows:
s21, providing a verification standard by using a reference frequency stabilized laser A in a national length standard device, and verifying the wavelength and relative frequency stability of output light of the frequency stabilized laser (103);
s22, measuring the output light of the frequency stabilized laser (103) and the output light of the wide-spectrum light source (101) through the film thickness measuring probe module (4), and enabling the measured return light to enter an optical path scanning device (604) for optical path scanning to obtain a frequency stabilized laser interference signal and a wide-spectrum interference signal;
s23, the optical path scanning amount of the optical delay line of the optical path scanning device (604) is detected and calculated by using the frequency-stabilized laser interference signal, and a wide-spectrum optical interference signal peak with the thickness information of the film to be detected is obtained in the process of optical path scanning of the optical path scanning device (604);
s24, calculating the optical path between different wide-spectrum light interference signal peaks in the wide-spectrum interference signal by using the optical path scanning device (604) after verification calculation to form a complete magnitude transfer system.
Preferably, the process of calibrating the wavelength of the output light of the frequency stabilized laser by using the reference frequency stabilized laser a in the national length standard in step S21 is as follows:
s101, adjusting output light beams of the frequency stabilized laser and the reference frequency stabilized laser A to enable output light of the frequency stabilized laser to be overlapped with output light of the reference frequency stabilized laser A;
s102, recording a frequency difference signal delta f generated by output light of the frequency stabilized laser and output light of the reference frequency stabilized laser A;
s103, setting a sampling time interval delta T and a total sampling time T, and calculating an average frequency difference by using a frequency difference signal delta f
Wherein, N represents the total sampling times of the frequency difference signal Δ f, and N is T/Δ T; Δ fiThe frequency difference signal of the output light of the ith sampling frequency stabilized laser and the output light of the reference frequency stabilized laser A is represented;
s104, calculating the wavelength value of output light of the frequency stabilized laser:
wherein λ isxThe wavelength value of the output light of the frequency stabilized laser is represented; f. ofxRepresents the output light frequency value of the output light of the frequency stabilized laser,
fsrepresenting the frequency nominal value of the reference frequency stabilized laser A;
s105, judging whether the wavelength value of the output light of the frequency stabilized laser meets the verification vacuum wavelength standard epsilon or not, if so, executing a step S22; otherwise, the frequency stabilized laser is reselected.
The process of verifying the wavelength stability of the output light of the frequency stabilized laser by using the reference frequency stabilized laser a in the national length standard device in the step S21 is as follows:
s111, adjusting output light beams of the frequency stabilized laser and the reference frequency stabilized laser A to enable output light of the frequency stabilized laser to be coincided with output light of the reference frequency stabilized laser A;
s112, setting 5 sampling time intervals delta tjJ is 1, 2, 3, 4, 5, and the sampling time intervals are: 0.1s, 1s, 10s, 100s and 1000 s;
s113, respectively calculating the relative frequency stability of the frequency stabilized laser in each sampling time interval, wherein the calculation formula of the relative frequency stability of the frequency stabilized laser in each sampling time interval is as follows:
wherein σjRepresenting the relative frequency stability of the frequency stabilized laser in the jth sampling time interval, NjRepresenting the total number of measurements corresponding to the jth sampling time interval; n is a radical ofj＝T/△tjWhere Ttotal sample time represents total sample time, fxjRepresenting the average frequency of the frequency stabilized laser over the total measurement time, when the sampling time interval is Deltat1When 0.1s, fx1＝fx；
The average frequency difference of output light of the frequency stabilized laser and the reference frequency stabilized laser A in the ith measurement within a certain sampling time is represented;
s113, judging whether the relative frequency stability of the frequency stabilized laser in each sampling time interval meets the verification relative frequency stability delta or not, and if yes, executing a step S22; otherwise, the frequency stabilized laser is reselected.
Preferably, when the optical path scanning device performs optical path scanning, the frequency stabilized laser signal interferes to generate a laser interference signal fringe, and the wavelength of the laser interference signal fringe is consistent with the wavelength λ of the output optical signal of the frequency stabilized laser; the formula for calibrating and calculating the optical path scanning quantity of the optical delay line of the optical path scanning device by the frequency stabilizing laser interference signal is as follows:
L＝Wλ
wherein, L represents the optical path scanning amount of the optical delay line of the optical path scanning device; w represents the number of fringes of laser interference signal fringes, and the optical path scanning quantity of an optical delay line of the optical path scanning device is verified to ensure the certainty degree of directly tracing to the national length measurement standard based on the common-optical-path self-calibration film thickness measuring device.
Preferably, the process of calculating the optical distance between different peaks of the wide-spectrum optical interference signal in the wide-spectrum interference signal by using the optical distance scanning device after verification calculation in step S24 is as follows:
s401, reading indication values of optical paths among different broad spectrum light interference signal peaks at different positions in an optical path scanning device after verification calculation;
s402, difference calculation is carried out on the indicating value quantity.
The optical path scanning device generates a frequency stabilization laser interference signal and a wide spectrum interference signal in the process of optical path scanning, the frequency stabilization laser interference signal verifies the optical path scanning amount of an optical delay line of the optical path scanning device, the verified optical delay line is equivalent to a ruler, and the calculation of the optical path between different wide spectrum optical interference signal peaks is read corresponding to indication values at different positions on the ruler and then is subjected to differential calculation.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
the invention provides a method for tracing the magnitude of a film thickness, which is based on the composition of a common-path self-calibration film thickness measuring device, utilizes a reference frequency-stabilized laser in a national length standard device to provide a verification standard, conducts verification from top to bottom, has information of the film thickness to be detected in a wide-spectrum light interference signal peak from the angle of tracing the magnitude of the film thickness, can trace the magnitude of the film thickness to an optical path between the wide-spectrum light interference signal peaks, can trace the optical path between the wide-spectrum light interference signal peaks to an optical path scanning quantity of an optical delay line of an optical path scanning device, can further trace the optical path scanning quantity of the optical delay line of the optical path scanning device to the wavelength and relative frequency stability of an output light signal of a frequency-stabilized laser, can trace the wavelength and relative frequency stability of the output light signal of the frequency-stabilized laser to the reference frequency-stabilized laser in a national length measuring standard device, a complete traceability system is formed, so that the traceability of the film thickness value to the national length measurement standard is completed from bottom to top, the film thickness value is directly traced to the national length measurement standard without the help of intermediate traceability conversion parameters, and the traceability chain is short and simple.
Drawings
FIG. 1 is a schematic structural diagram of a common-path self-calibration thin film thickness measuring device according to an embodiment of the present invention;
FIG. 2 is a diagram of an optical path inside a measurement probe module when a film to be measured is not inserted in the embodiment of the present invention;
FIG. 3 is a diagram of an optical path inside a probe module when a film to be tested is inserted according to an embodiment of the present invention;
FIG. 4 is a flow chart illustrating a method for tracing the source of a film thickness according to an embodiment of the present invention;
FIG. 5 is a flow chart illustrating a method for transferring a magnitude of a film thickness according to an embodiment of the present invention;
fig. 6 is a waveform diagram of a wide-spectrum optical interference signal and a frequency-stabilized laser interference signal obtained during scanning of an optical delay line.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for better illustration of the present embodiment, certain parts of the drawings may be omitted, enlarged or reduced, and do not represent actual dimensions;
it will be understood by those skilled in the art that certain well-known descriptions of the figures may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Example 1
The method is used for tracing the magnitude of the thickness of the film measured by the common-path self-calibration film thickness measuring device, the common-path self-calibration film thickness measuring device is shown in figure 1 and comprises a light source output module 1, a beam splitting coupler 2, a first measuring interferometer coupler 3, a film thickness measuring probe module 4, a second measuring interferometer coupler 5, an interference and demodulation module 6 and an acquisition and control module 7, and an optical path scanning device 604 is arranged in the interference and demodulation module 6; the light source output module 1 comprises a wide spectrum light source 101 and a frequency stabilized laser 103, output light of the wide spectrum light source 101 and the frequency stabilized laser 103 is divided into two paths through a beam splitting coupler 2, the two paths enter a film thickness measuring probe module 4 through a first measuring interferometer coupler 3 and a second measuring interferometer coupler 5 respectively for parameter measurement, return light measured by the film thickness measuring probe module 4 enters an optical path scanning device 604 of an interference and demodulation module 6 through the first measuring interferometer coupler 3 and the second measuring interferometer coupler 5 respectively for scanning optical path matching to obtain a frequency stabilized laser interference signal and a wide spectrum light interference signal, and the frequency stabilized laser interference signal and the wide spectrum light interference signal are transmitted to the acquisition and control module 7.
In the present embodiment, the light source output module 1 is composed of a broad spectrum light source 101 with a central wavelength of 1310nm, a narrowband frequency-stabilized laser light source 103 with a wavelength of 633nm, a first isolator 102 with an operating wavelength of 1310nm, a second isolator 104 with an operating wavelength of 633nm, and a first wavelength division multiplexer 105 with operating wavelengths of 1310nm and 633 nm. The wide-spectrum light source 101 with the central wavelength of 1310nm is used as a measuring light beam, and the common-path self-calibration film thickness measuring device is used for realizing absolute measurement of the film thickness; the narrow-band frequency stabilization laser light source 103 with the wavelength of 633nm is used as a light path correction light beam and is mainly used for tracing the subsequent film thickness measurement.
Referring to fig. 1, light emitted by two light sources respectively enters a first wavelength division multiplexer 105 through a first isolator 102 and a second isolator 104, and the light is combined into a beam splitting coupler 2 with a splitting ratio of 3dB, and the light is equally divided into two paths to enter a film thickness measuring probe module 4 through a first measuring interferometer coupler 3 with a splitting ratio of 3dB and a second measuring interferometer coupler 5 with a splitting ratio of 3 dB; the ratio of the reflectivity of the lens end faces of the first measuring probe 401 and the second measuring probe 402 to the transmissivity is 50: 50; the measurement light returned from the first measurement probe 401 and the 2 nd measurement probe 402 is transmitted to the first measurement interferometer 6A and the second measurement interferometer 6B via the first measurement interferometer coupler 3 having a splitting ratio of 3dB and the second measurement interferometer coupler 5 having a splitting ratio of 3dB, respectively, and is interfered at the first demodulation interferometer coupler 601 having a splitting ratio of 3dB and the second demodulation interferometer coupler 607 having a splitting ratio of 3dB, respectively, by optical path scanning by the optical path scanning device 604. The second wavelength division multiplexer 707 and the third wavelength division multiplexer 708 separate the white light measuring beam with the center wavelength of 1310nm and the laser correction beam with the wavelength of 633nm, and finally the white light measuring beam and the laser correction beam are obtained by the first photodetector 703, the second photodetector 704, the third photodetector 705 and the fourth photodetector 706. The photodetector transmits the collected signal to the computer 701 through the data acquisition card 702 for demodulation, and the computer 701 is also responsible for driving the position scanning device 604.
When the film 403 to be measured is not inserted, the output light is split by the beam splitting coupler 2 with the splitting ratio of 3dB, and the light respectively passes through the first measuring interferometer coupler 3 with the splitting ratio of 3dB and the second measuring interferometer coupler 5 with the splitting ratio of 3dB and enters the first measuring probe 401 and the second measuring probe 402. As shown in fig. 2, a beam 411 reflected by the inner surface of the lens of the first measuring probe 401 itself, and a beam 412 reflected by the outer surface of the lens of the second measuring probe 402 are input into the first demodulation interferometer 6A through the first measuring interferometer coupler 3; the light beams 421 reflected by the second measuring probe 402 itself inside the lens, the light beams 422 reflected by the outer surface of the first measuring probe 401 lens are input into the second demodulation interferometer 6B via the second measuring interferometer coupler 5.
The light beam is transmitted in the first demodulation interferometer 6A in the following manner: inputting the return light of the film thickness measuring probe 401 into a first demodulation interferometer coupler 601 with a splitting ratio of 3dB by a first measurement interferometer coupler 3 with a splitting ratio of 3dB, wherein the return light of the first measurement probe 401 is reflected by a forward movable mirror 604a and a first Faraday mirror 605, and when the forward optical scanning mirror 604a and the reverse movable optical scanning mirror 604b move, the optical path lengths of the reflected light 411 and the reflected light 412 are completely matched, a white light interference fringe is formed on a first photodetector 703, and a laser interference fringe is formed on a second photodetector 704; the transmission of the light beam in the second demodulation interferometer 6B is: the light returned from the film thickness measuring probe 402 is input to the second demodulation interferometer coupler 607 having a splitting ratio of 3dB by the second measurement interferometer coupler 5 having a splitting ratio of 3dB, and is reflected by the reverse movable optical mirror 604b and the second faraday mirror 606, and when the forward optical scanning mirror 604a and the reverse movable optical mirror 604b move, the optical paths of the reflected light 421 and the reflected light 422 are perfectly matched, and a white light interference fringe is formed on the 3 rd photodetector 705 and a laser interference fringe is formed on the 4 th photodetector 706. The absolute distance H between the two measuring probes can be obtained by demodulating the white light interference signal.
When the film 403 to be measured is inserted, incident light is split by the beam splitting coupler 2 with the splitting ratio of 3dB, and light enters the first measuring probe 401 and the second measuring probe 402 through the first measuring interferometer coupler 3 with the splitting ratio of 3dB and the second measuring interferometer coupler 5 with the splitting ratio of 3dB, respectively. As shown in FIG. 3, a beam 413 reflected by the inner surface of the lens of the first measuring probe 401 and a beam 414 reflected by the front surface 403a of the film to be measured are inputted to the first demodulation interferometer 6A; the light beams 423 reflected by the lens inner surface of the second measuring probe 402 and 424 reflected by the back surface 403B of the film to be measured are inputted into the second demodulation interferometer 6B. The light beam is transmitted in the first demodulation interferometer 6A in the following manner: inputting the return light of the film thickness measuring probe 401 into a first demodulation interferometer coupler 601 with a splitting ratio of 3dB by a first measuring interferometer coupler 3 with a splitting ratio of 3dB, wherein the return light of the first measuring probe 401 is reflected by a forward movable mirror 604a and a first Faraday mirror 605, and when the forward optical scanning mirror 604a and the reverse movable optical scanning mirror 604b move, the optical path of the reflected light 413 and the reflected light 414 are completely matched, a white light interference fringe is formed on a first photodetector 703, and a laser interference fringe is formed on a second photodetector 704; the transmission of the light beam in the second demodulation interferometer 6B is: the light returned from the film thickness measuring probe 402 is input to the second demodulation interferometer coupler 607 having a splitting ratio of 3dB by the second measurement interferometer coupler 5 having a splitting ratio of 3dB, and the light is reflected by the reverse movable optical mirror 604b and the second faraday mirror 606, and when the forward optical scanning mirror 604a and the reverse movable optical mirror 604b move, the optical paths of the reflected light 423 and the reflected light 424 are perfectly matched, and a white light interference fringe is formed on the third photodetector 705 and a laser interference fringe is formed on the fourth photodetector 706. By demodulating the white light interference signal, the distance H1 between the front surface 403a of the film to be measured of the first measurement probe 401 and the distance H2 between the front surface 403b of the film to be measured of the 2 nd measurement probe 402 are obtained, respectively. Thus, the film thickness is determined by the two measurements described above, i.e., H- (H1+ H2).
Fig. 4 is a schematic flow chart of a method for tracing the magnitude of a film thickness, the method includes:
s11, the thickness of the film 403 to be measured can be traced upwards to the optical path difference between different wide-spectrum light interference signal peaks;
s12, the optical path between the interference signal peaks of the broad spectrum light can be traced upwards to the optical path scanning amount of the optical path scanning device 604;
s13, the optical path scanning quantity of the optical path scanning device 604 can be traced upwards to the wavelength and relative frequency stability of the output light of the 633nm frequency stabilized laser 103 of the working measurement standard;
s14, the wavelength and the relative frequency stability of output light of the 633nm frequency stabilized laser 103 of the working measurement standard can be traced upwards to a reference frequency stabilized laser A in a national length measurement standard appliance; in this embodiment, the reference frequency stabilized laser a is a 633nm frequency stabilized laser in the national length standard.
A flow diagram of a method for magnitude transfer of film thickness as shown in fig. 5, the method comprising:
s21, according to the 633nm frequency stabilized laser verification specification (JJG 353-2006), verifying the wavelength and the relative frequency stability of output light of the frequency stabilized laser 103 by using a reference frequency stabilized laser A in a national length standard device, wherein the output wavelength and the wavelength stability of the 633nm frequency stabilized laser in the national length measurement benchmark device are known and the performance of the 633nm frequency stabilized laser is 10 times better than that of the 633nm frequency stabilized laser used by a measurement system;
s22, measuring the output light of the frequency stabilized laser 103 and the output light of the wide-spectrum light source 101 after verification through the film thickness measuring probe module 4, and enabling the measured return light to enter the optical path scanning device 604 for optical path scanning to obtain a frequency stabilized laser interference signal and a wide-spectrum interference signal;
s23, the frequency stabilized laser interference signal is used for carrying out verification calculation on the optical path scanning amount of the optical delay line of the optical path scanning device 604, and a wide-spectrum optical interference signal peak with the thickness information of the film to be detected is obtained in the process of carrying out optical path scanning by the optical path scanning device 604;
and S24, calculating the optical path between different wide-spectrum light interference signal peaks in the wide-spectrum interference signal by using the optical path scanning device 604 after verification calculation to form a traceability system.
In this embodiment, the process of calibrating the wavelength of the output light of the frequency stabilized laser 103 is as follows:
s101, adjusting output light beams of the frequency stabilized laser 103 and the reference frequency stabilized laser A to enable output light of the frequency stabilized laser 103 to coincide with output light of the reference frequency stabilized laser A;
s102, recording a frequency difference signal delta f generated by output light of the frequency stabilized laser 103 and output light of the reference frequency stabilized laser A;
s103, setting a sampling time interval delta T and a total sampling time T, and calculating an average frequency difference by using a frequency difference signal delta f
Where N represents the total sampling number of the frequency difference signal Δ f, where N is T/Δ T, and in this embodiment, Δ T is 0.1s, and T is 3 h; Δ fiA frequency difference signal representing output light of the ith sampling frequency stabilized laser 103 and the reference frequency stabilized laser A;
s104, calculating the wavelength value of the output light of the frequency stabilized laser 103:
wherein λ isxA wavelength value representing the output light of the frequency stabilized laser (103); f. ofxRepresents the value of the output light frequency of the output light of the frequency stabilized laser 103,
fsrepresenting the frequency nominal value of the reference frequency stabilized laser A;
s105, judging whether the wavelength value of the output light of the frequency stabilized laser 103 meets the verification vacuum wavelength standard epsilon or not, if so, executing a step S2; otherwise, the frequency stabilized laser 103 is reselected.
The process of calibrating the wavelength stability of the output light of the frequency stabilized laser 103 is as follows:
s111, adjusting output light beams of the frequency stabilized laser 103 and the reference frequency stabilized laser A to enable output light of the frequency stabilized laser 103 to coincide with output light of the reference frequency stabilized laser A;
s112, setting 5 sampling time intervals delta tjJ is 1, 2, 3, 4, 5, and the sampling time intervals are: 0.1s, 1s, 10s, 100s and 1000 s;
s113, respectively calculating the relative frequency stability of the frequency stabilized laser 103 in each sampling time interval, wherein the calculation formula of the relative frequency stability of the frequency stabilized laser 103 in each sampling time interval is as follows:
wherein σjRepresents the relative frequency stability of the frequency stabilized laser (103) in the jth sampling time interval, NjRepresenting the total number of measurements corresponding to the jth sampling time interval; n is a radical ofj＝T/△tjThe Ttotal sampling time represents the total sampling time, in this embodiment, T takes 3 hours; f. ofxjRepresents the average frequency of the frequency stabilized laser (103) over the total measurement time, when the sampling time interval is Deltat1When 0.1s, fx1＝fx；
The average frequency difference of the output light of the frequency stabilized laser (103) and the reference frequency stabilized laser A in a certain sampling time at the ith measurement is represented;
s113, judging whether the relative frequency stability of the frequency stabilized laser 103 in each sampling time interval meets the verification relative frequency stability delta or not, and if yes, executing a step S2; otherwise, the frequency stabilized laser 103 is reselected.
The verification vacuum wavelength standard epsilon and the verification relative frequency stability delta are determined according to the verification standard (JJG 353-2006) of the frequency stabilized laser with the wavelength of 633nm according to the actual situation.
When the optical path scanning device 604 performs optical path scanning, the frequency stabilized laser signal interferes to generate a laser interference signal fringe, and the wavelength of the laser interference signal fringe is consistent with the output optical signal compensation λ of the frequency stabilized laser 103. The formula for calibrating and calculating the optical path scanning quantity of the optical delay line of the optical path scanning device 604 by the frequency-stabilized laser interference signal is as follows:
L＝Wλ
wherein L represents the optical path scanning amount of the optical delay line of the optical path scanning device 604; w represents the number of fringes of the laser interference signal fringe. Broad spectrum light interference signals occur and only at the aplanatic path.
In this embodiment, the process of calculating the optical distances between different peaks of the wide-spectrum optical interference signal in the wide-spectrum interference signal by using the optical distance scanning device 604 after verification calculation is as follows:
s401, reading indication values of optical paths among different broad spectrum light interference signal peaks at different positions in an optical path scanning device 604 after verification calculation;
s402, difference calculation is carried out on the indicating value quantity.
When the optical path scanning device performs optical path scanning, as shown in fig. 6, a 633nm frequency stabilization laser interference signal and a 1310nm wide spectrum optical interference signal are obtained at the same time, a characteristic signal peak with information of the thickness of the film to be measured is obtained by utilizing the 1310nm wide spectrum optical interference, the optical path delay of the optical path scanning device is realized by utilizing the 633nm frequency stabilization laser interference, and the measurement result of the thickness of the film is traced upwards to the optical path delay of the optical path scanning device; the optical path delay amount of the optical path scanning device is traced upwards to the wavelength and the wavelength stability of the output optical signal of the 633nm frequency stabilized laser used by the measuring system; the wavelength and the wavelength stability of the output optical signal of the 633nm frequency stabilized laser used by the measuring system are traced upwards to the 633nm frequency stabilized laser in the national length measuring standard device.
The positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (6)
1. A method for tracing the magnitude of a film thickness is characterized in that the method is used for tracing the magnitude of the film thickness measured by a common-path self-calibration film thickness measuring device, the common-path self-calibration film thickness measuring device comprises a light source output module (1), a beam splitting coupler (2), a first measuring interferometer coupler (3), a film thickness measuring probe module (4), a second measuring interferometer coupler (5), an interference and demodulation module (6) and an acquisition and control module (7), and an optical path scanning device (604) is arranged in the interference and demodulation module (6); the light source output module (1) comprises a wide-spectrum light source (101), a frequency stabilized laser (103), a first isolator (102), a second isolator (104) and a first wavelength division multiplexer (105), output light of the wide-spectrum light source (101) and the frequency stabilized laser (103) respectively enters the first wavelength division multiplexer (105) through the first isolator (102) and the second isolator (104), a beam of the synthesized output light enters the beam splitting coupler (2), the output light is divided into two paths through the beam splitting coupler (2), the two paths of the output light respectively enter the film thickness measuring probe module (4) through the first measuring interferometer coupler (3) and the second measuring interferometer coupler (5) for parameter measurement, the film thickness measuring probe module (4) comprises a first measuring probe (401) and a second measuring probe (402), the output light divided into two paths through the beam splitting coupler (2) respectively enters the first measuring probe (401) and the second measuring probe (402) for measurement, returning light measured by the film thickness measuring probe module (4) enters an optical path scanning device (604) of the interference and demodulation module (6) through the first measuring interferometer coupler (3) and the second measuring interferometer coupler (5) to be scanned and matched with an optical path, so that a frequency stabilization laser interference signal and a wide spectrum light interference signal are obtained, and the frequency stabilization laser interference signal and the wide spectrum light interference signal are transmitted to the acquisition and control module (7); the common-path self-calibration film thickness measuring device utilizes the wide-spectrum light interference signal to measure the film thickness and utilizes the frequency-stabilized laser interference signal to demodulate and trace the optical path between different wide-spectrum light interference signal peaks;
the tracing method at least comprises the following steps:
s11, the thickness of the film (403) to be measured can be traced upwards to the optical path difference between different wide-spectrum optical interference signal peaks;
s12, the optical path difference between the interference signal peaks of the broad spectrum light can be traced upwards to the optical path scanning amount of the optical path scanning device (604);
s13, the optical path scanning quantity of the optical path scanning device (604) can be traced upwards to the wavelength and relative frequency stability of the output light of the frequency stabilized laser (103) of the working metering standard device;
s14, the wavelength and the relative frequency stability of output light of the frequency stabilized laser (103) of the working measurement standard device can be traced upwards to a reference frequency stabilized laser A in a national length measurement standard device.
2. The method for tracing the magnitude of the film thickness according to claim 1, wherein the performance of the reference frequency stabilized laser A in the national length measurement reference instrument of step S14 is 3-10 times of the performance of the frequency stabilized laser (103) of the working measurement standard in the common-path self-calibration film thickness measuring device.
3. The method of claim 1, wherein the reference frequency stabilized laser A in the national length measurement standard device has a value transmission characteristic as follows:
s21, providing a verification standard by using a reference frequency stabilized laser A in a national length measurement standard instrument, and verifying the wavelength and relative frequency stability of output light of the frequency stabilized laser (103);
s22, measuring the output light of the frequency stabilized laser (103) and the output light of the wide-spectrum light source (101) through the film thickness measuring probe module (4), and enabling the measured return light to enter an optical path scanning device (604) for optical path scanning to obtain a frequency stabilized laser interference signal and a wide-spectrum interference signal;
s23, the optical path scanning amount of the optical delay line of the optical path scanning device (604) is detected and calculated by using the frequency-stabilized laser interference signal, and a wide-spectrum optical interference signal peak with the thickness information of the film to be detected is obtained in the process of optical path scanning of the optical path scanning device (604);
s24, calculating the optical path difference between different wide-spectrum optical interference signal peaks in the wide-spectrum interference signal by using the optical path scanning device (604) after verification calculation to form a complete magnitude transfer system.
4. The method for tracing the magnitude of the film thickness according to claim 3, wherein when the optical path scanning device (604) performs optical path scanning, the output optical signals of the frequency stabilized laser (103) interfere to generate laser interference signal fringes, and the wavelength of the laser interference signal fringes is consistent with the output optical signal wavelength λ of the frequency stabilized laser (103).
5. The method for tracing the magnitude of the film thickness according to claim 4, wherein the formula for the frequency stabilized laser interference signal to verify and calculate the optical path scanning amount of the optical delay line of the optical path scanning device (604) is as follows: l ═ W λ;
wherein L represents an optical path scanning amount of an optical delay line of an optical path scanning device (604); w represents the number of fringes of the laser interference signal fringe.
6. The method for tracing the magnitude of the film thickness according to claim 3, wherein said step S24 of calculating the optical path difference between different peaks of the wide-spectrum optical interference signal in the wide-spectrum interference signal by using the optical path scanning device (604) after calibration calculation comprises:
s401, reading indication values of optical path differences among different broad spectrum light interference signal peaks at different positions in an optical path scanning device (604) after verification calculation;
s402, difference calculation is carried out on the indicating value quantity.
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| US6614534B1 (en) * | 1999-12-14 | 2003-09-02 | Eastman Kodak Company | Method and apparatus for combined measurement of surface non-uniformity index of refraction variation and thickness variation |
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