CN107339943A - The common light path self calibration apparatus for measuring thickness of thin film and measuring method of palarization multiplexing - Google Patents

Abstract

The invention provides a polarization multiplexing common optical path self-calibrating film thickness measuring device and a measuring method. It includes light source output module, film thickness measurement probe module, demodulation interferometer module, polarization beam splitting module, and acquisition and control module. The invention adopts polarization multiplexing technology, and the two probes use orthogonal polarized light. The measuring probe can realize the transmission and reflection of transmitted light. When there is no film to be measured, the absolute distance H between the two probes can be measured. The film to be measured is placed between the two probes to achieve the measurement of the absolute distances H1 and H2 between the two probes and the front and rear surfaces of the film to be measured. Measurement; the thickness d of the film to be measured can be determined by d=H‑(H1+H2). The invention can measure the thickness of the film to be measured without the need for calibration objects. The design of the common optical path overcomes the influence of mechanical instability within the system and changes in the external environment during the measurement process. It has self-calibration and simple identification of characteristic white light interference peaks. , large dynamic range, traceable measurement results and other advantages.

Description

Polarization multiplexing common optical path self-calibration film thickness measurement device and measurement method

technical field

The invention relates to an optical measuring device, in particular to a film thickness measuring device. Specifically, it is a polarization multiplexing common optical path self-calibration film thickness measuring device.

Background technique

With the vigorous development of material science and technology, in order to meet the urgent needs of microelectronics, optoelectronics, new energy and other fields, thin films are used in optical engineering, mechanical engineering, communication engineering, biological engineering, aerospace engineering, chemical engineering, medical engineering and other fields. widely used. One of the core and key parameters of thin film materials is thickness, which not only plays a key role in the preparation of thin films, but also basically determines the mechanical, electromagnetic, photoelectric and optical properties of thin films.

In 1961, N. Schwartz and others proposed a contact probe method that uses high-precision mechanical stylus to move on the surface of the object to sense the change of the surface profile (N. Schwartz, R. Brown, "A Stylus Method for Evaluating the Thickness of Thin Films and Substrate Surface Roughness,” in Transactions of the Eighth Vacuum Symposium and Second International Congress (Pergamon, New York, 1961), pp.836–845.), this method has the advantages of good stability, high resolution, and large measurement range ; However, since the probe method includes a probe based on mechanical motion, secondary processing is required when measuring the thin film. In addition, the movement of the probe on the surface of the thin film will also cause certain damage to the thin film. Therefore, the non-contact measurement method quickly replaced the contact measurement method to measure the thickness of the film.

In 2013, Ma Xizhi and others from Nanjing University of Aeronautics and Astronautics disclosed an ultrasonic film thickness measuring instrument and its measurement method (Chinese patent application number: 201310198294.9). The thickness of the oil film is measured by measuring the correlation characteristics of the reflected pulse; however, this method is only suitable for the measurement of the liquid model, and different models need to be established for films with different thickness ranges, and the demodulation is difficult.

The optical measurement method has the advantage of high precision, and it has gradually been widely used in the measurement of film thickness. In 2012, Qu Lianjie and others from Beijing BOE Optoelectronics Technology Co., Ltd. disclosed a film thickness device and method (Chinese patent application number: 201210080756.2). Spectroscopic treatment is performed to irradiate the surface of the film, and the thickness of the film is measured by measuring the characteristics of different reflected light. The method expands the spectrum range of the sampling point of the device for measuring the film thickness and improves the resolution.

As a part of the optical measurement method, white light interferometry has gradually begun to develop in the field of film thickness measurement due to its absolute measurement advantages. The basic principle of white light interferometry is: a scanning mirror is connected to the end of one arm of the white light interferometer as the sensing arm, the length of the other arm is fixed as the reference arm, and the length of the sensing arm is changed by moving the scanning mirror. When the optical path of the transmitted light matches the optical path of the transmitted light in the reference arm, the maximum interference peak appears, and the measurement of related parameters is realized by identifying the position of the peak. In 2008, Peter J.de Groot et al. of Zygo Company of the United States disclosed a scanning interferometry for thin film thickness and surface measurements (Scanning interferometry for thin film thickness and surface measurements, US Patent 7468799), which uses the principle of white light interference The film thickness measurement method uses the Fourier transform method to extract two peaks from the interference light intensity map. This method is not affected by the film thickness. The light source coherence length of the thin film. In 2014, Jia Chuanwu of Shandong University and others disclosed a system for measuring film thickness by wide-spectrum optical interferometry (Chinese patent application number: 201410290494.1). Luo interferometer, by measuring the Fabry-Perot cavity length before and after placing the film under the mirror, the thickness of the film to be tested can be obtained. This method has a simple structure and high measurement accuracy, but due to the need to The film is placed under the mirror, which is easy to damage the morphology of the film surface.

Contents of the invention

The purpose of the present invention is to provide a common optical path self-calibration film thickness measurement device with high precision, self-calibration, simple identification of characteristic white light interference peaks, traceability, polarization multiplexing in dynamic range. The purpose of the present invention is also to provide a film thickness measurement method.

The purpose of the present invention is achieved like this:

It includes a light source output module 1, a film thickness measurement probe module 6, a demodulation interferometer module 7, a polarization beam splitting module 8, and an acquisition and control module 9; the output light of the light source output module 1 is input to the polarization maintaining module through a 45° polarizer 2 In the coupler 3; the polarization-maintaining coupler 3 divides the incident light into two paths and enters the first measuring probe 601 and the second measuring probe of the film thickness measuring probe module 6 through the 0° polarizer 4 and the 90° polarizer 5 respectively Carry out the measurement of relevant parameter in 602; Input in the demodulation interferometer module 7 through the return light of the 1st measurement probe 601 and the 2nd measurement probe 602; The matching of the optical path; the interference signal of the matching optical path is input into the polarization beam splitting module 8 to realize the separation of different polarization states and different wavelengths of interference light; the separated interference signal is collected by the acquisition and control module 9 to calculate related parameters.

The present invention may also include:

1. The light source output module 1 is composed of a wide-spectrum light source 101, a first isolator 102, a narrow-band frequency-stabilized laser light source 103, a second isolator 104, and a first wavelength division multiplexer 105. The wide-spectrum light source 101 and the first The first isolator 102 is connected, the narrowband frequency-stabilized laser source 103 is connected to the input end of the second isolator 104, the output end of the first isolator 102 and the second isolator 104 are respectively connected to the first input of the first wavelength division multiplexer 105 Terminal 1a and the second input terminal 1b are connected.

2. The characteristics of each light source in the light source output module 1 are: the half-spectrum width of the wide-spectrum light source 101 is greater than 45nm, and the output power is greater than 2mW; the half-spectrum width of the narrow-band frequency-stabilized laser light source 103 is less than 1pm, and the output power is greater than 2mW; the wide-spectrum light source 101 and the narrow-band frequency-stabilized laser light source 103 have different center wavelengths, and the spectra of the two have no overlap within the half-spectrum width.

3. The film thickness measuring probe 6 is composed of a first measuring probe 601 and a second measuring probe 602; the first measuring probe 601 and the second measuring probe 602 can simultaneously realize the transmission and reflection of the transmitted light, and the reflection of the transmitted light rate between 20% and 80%; the first measuring probe 601 and the second measuring probe 602 can work on both the fast axis and the slow axis of the polarization-maintaining fiber; Coincidence; when the device under test 603 is placed for measurement, it is perpendicular to the outgoing rays of the first measuring probe 601 and the second measuring probe 602; the first measuring probe 601 is connected to the output end of the 0° analyzer 4, and the second measuring probe 602 is connected with the output end of 90° polarizer 5 .

4. The demodulation interferometer module 7 is composed of a polarization-maintaining coupler 701, a polarization-maintaining self-focusing lens 702, a movable single-sided mirror 703, and a position scanning device 704. Both the fast axis and the slow axis can work, and can realize reflection and transmission at the same time. The light reflectivity of the lens is between 20% and 80%. The light collected by the first measurement probe 601 and the second test probe 602 is respectively passed through The second output end 3b of the polarization maintaining coupler 3 is input into the second input end 7b of the polarization maintaining coupler 701, the third output end 7c of the polarization maintaining coupler 701 is connected with the polarization maintaining self-focusing lens 702, the first of the polarization maintaining coupler 701 The output end 7a is connected to the input end of the polarization beam splitter prism 803; the polarization maintaining self-focusing lens 702, the movable single-sided mirror 703 and the demodulation interferometer coupler 701 together form the demodulation interferometer; the scanning range of the position scanning device 704 table top L can meet the requirement that when the film thickness measurement probe module is not inserted into the film 603 to be measured, the demodulation interferometer can realize the optical path matching of the reflected light from the inner and outer surfaces of different probe lenses.

5. The characteristics of connecting optical fibers in the optical path are: the pigtail at the output end of the broadband light source 101, the narrow-band frequency-stabilized laser light source 103, the pigtail at each port of the first isolator 102, the pigtail at each port of the second isolator 104, and the first WDM Multiplexer 105, 45° polarizer 2 input pigtails, each port pigtails are single-mode fibers; 45° polarizer 2 output pigtails, polarization maintaining coupler 3 ports pigtails, 0° polarization analyzer 4 input and output pigtails, 90° polarizer 5 input and output pigtails, first measuring probe 601 pigtails, second measuring probe 602 pigtails, polarization maintaining coupler 701 each port pigtails, polarization maintaining autofocus Lens 702 pigtail, polarization beam splitter 803 each port pigtail, second wavelength division multiplexer 801 each port pigtail, third wavelength division multiplexer 802 each port pigtail first photodetector 903 pigtail, second The pigtails of the photodetector 904, the pigtails of the third photodetector 905, and the pigtails of the sixth photodetector 906 are all polarization-maintaining fibers.

Thin film thickness measuring method of the present invention is:

1. When the film 603 to be tested is not inserted, drive the optical path position scanning device 704 to scan the optical path, so that the internal reflected light 611 of the first measuring probe 601 and the reflected light 612 on the outer surface of the second measuring probe 602 are matched in optical path. 2 The internal reflected light 621 of the measuring probe 602 is matched with the reflected light 622 on the outer surface of the first measuring probe 601; the acquisition and control module 9 demodulates and records the relevant parameters to obtain the absolute distance H between the two measuring probes;

2. Insert the film 603 to be measured between the first measuring probe 601 and the second measuring probe 602, the film 603 to be measured is perpendicular to the outgoing rays of the first measuring probe 601 and the second measuring probe 602; drive the optical path position scanning device 704 to carry out Optical path scanning, so that the optical path matching is performed between the internal reflected light 613 of the first measuring probe 601 and the reflected light 614 on the front surface 603a of the film to be measured, and the internal reflected light 623 of the second measuring probe 602 is matched with the reflected light 624 on the rear surface 603b of the film to be measured. Optical path matching; through the acquisition and control module 9, the relevant parameters are demodulated and recorded, and the distance H1 of the first measuring probe 601 to the front surface of the film to be tested 603a, and the distance H2 of the second measuring probe 602 to the front surface of the film to be tested 603b are obtained;

3. Determine the film thickness d from the above two measured values, that is, d=H-(H1+H2).

The self-calibrating film thickness measurement device with polarization multiplexing and common optical path provided by the present invention has the characteristics of high precision, self-calibration, simple identification of characteristic white light interference peaks, traceability, and large dynamic range. Due to the polarization characteristics of the probe light, it can be used for high-precision measurement of the thickness of transparent and opaque films in film production and applications.

The invention provides a self-calibrating film thickness measuring device with polarization multiplexing and common optical path, which realizes the non-contact measurement of film thickness. Firstly, since the two measuring probes can realize the transmission and reflection of the incident light at the same time, the absolute distance H between the measuring probes can be directly measured; then the film to be measured is inserted into the middle of the two measuring probes, and the distance between the two measuring probes before and after the film to be measured is respectively obtained. The absolute distances H1 and H2 between the surfaces; thus the thickness of the film to be measured d=H-(H1+H2). In the present invention, the polarized light of different polarization states produced by the polarizer and the analyzer is used for parameter measurement between different probes, so that the identification of the characteristic white light interference peak is simpler; the return light of the two probes shares the same demodulation interference device, effectively avoiding The impact of changes in the external environment is eliminated; the optical path adopts a dual light source structure, which improves the absolute measurement accuracy, realizes the further expansion of the dynamic range, overcomes the error caused by the instability of the mechanical system during the measurement process, and improves the stability of the measurement; Through the optimized design of the light reflectance and transmittance of the end surface of the measuring probe, the high-precision measurement of the thickness of transparent and opaque films can be realized without calibrating samples during measurement.

Compared with prior art, the beneficial effect of the present invention is:

(1) The measuring probe of the present invention can realize the transmission and reflection of the incident light at the same time, and can directly realize the self-calibration of the measuring system, so that when measuring, the thickness of the film to be measured can be directly measured without a standard sample.

(2) The present invention proposes the method for measuring film thickness based on the dual-band optical fiber optical interferometry of wide-spectrum light source and narrow-band frequency-stabilized laser. Under the premise of ensuring high-precision measurement of film absolute thickness, it realizes the expansion of its measurement dynamic range and overcomes the The error caused by mechanical instability in the measurement process improves the absolute accuracy of the measurement and the stability of the test, and ensures that the optical test of the thin film can be traced.

(3) The present invention adopts polarization multiplexing technology, adopts polarized light of different polarization states between different measuring probes to realize the thickness measurement of transparent film and opaque film, white light interference characteristic peak identification is simpler, and the demodulation algorithm is further simplified .

Description of drawings

Fig. 1 is a schematic diagram of a polarization multiplexing common optical path self-calibration film thickness measurement device.

Figure 2 is a diagram of the internal optical path of the measuring probe module when no film to be measured is loaded.

Fig. 3 is a diagram of the internal optical path of the measuring probe module when the film to be measured is loaded.

Figure 4 is a diagram of the internal light path of the demodulation interferometer.

Fig. 5 is a schematic diagram of the principle of laser interference signal traceability.

Fig. 6 is a schematic diagram of a distance measurement method based on the principle of white light interference when the film to be tested is not loaded.

detailed description

The polarization multiplexing common optical path self-calibration film thickness measurement device of the present invention consists of five parts: a light source output module 1, a film thickness measurement probe module 6, a demodulation interferometer module 7, a polarization beam splitting module 8, and an acquisition and control module 9. composition. The components of each module are: (1) The light source output module 1 is composed of a wide-spectrum light source 101, a first isolator 102, a narrowband frequency-stabilized laser light source 103, a second isolator 104, and a first wavelength division multiplexer 105; 2) The film thickness measuring probe module 6 is composed of the first measuring probe 601 and the second measuring probe 602; (3) The demodulation interferometer module 7 consists of a polarization maintaining coupler 701, a polarization maintaining self-focusing lens 702, and a movable single-sided Reflector 703 and position scanning device 704 are formed; (4) polarization beam splitting module 8 is made up of the 2nd coupler 801, the 3rd coupler 802 and polarization beam splitting prism 803; (5) collection and control module 9 is made up of computer 901 , a data acquisition card 902, a first photodetector 903, a second photodetector 904, a third photodetector 905 and a fourth photodetector 906.

The output light of the light source output module 1 is input into the polarization maintaining coupler 3 through the 45° polarizer 2; the polarization maintaining coupler 3 divides the incident light into two paths and passes through the 0° polarizer 4 and the 90° polarizer 5 respectively Enter the first measurement probe 601 and the second measurement probe 602 of the film thickness measurement probe module 6 to measure related parameters; the return light via the first measurement probe 601 and the second measurement probe 602 is input into the demodulation interferometer module 7 The optical path matching is realized by demodulating the scanning of the position scanning device 704 in the interferometer module 7 . The interference signal with optical path matching is input into the polarization beam splitting module 8 to realize the separation of interference light with different polarization states and different wavelengths; the separated interference signal is collected by the acquisition and control module 9 to calculate related parameters.

The wide-spectrum light source 101 in the light source output module 1 is connected to the first isolator 102 , and the narrow-band frequency-stabilized laser light source 103 is connected to the second isolator 104 . The first isolator 102 and the second isolator 104 are respectively connected to the input terminals 1a and 1b of the first wavelength division multiplexer 105 . The half-spectrum width of the wide-spectrum light source 101 is greater than 45nm, and the output power is greater than 2mW; the half-spectrum width of the narrow-band frequency-stabilized laser source 103 is less than 1pm, and the output power is greater than 2mW. The wide-spectrum light source 101 and the narrow-band frequency-stabilized laser light source 103 have different center wavelengths, and the spectra of the two have no overlap within the half-spectrum width.

The first measuring probe 601 and the second measuring probe 602 in the film thickness measuring probe module 6 can realize the transmission and reflection of the transmitted light at the same time, and the reflectance of the transmitted light is between 20% and 80%. The first measuring probe 601 and the second measuring probe 602 can work on both the fast axis and the slow axis of the polarization maintaining fiber. The outgoing rays of the first measuring probe 601 and the second measuring probe 602 coincide with each other; when the device under test 603 is placed for measurement, they are perpendicular to the outgoing rays of the first measuring probe 601 and the second measuring probe 602 respectively. The first measuring probe 601 is connected to the output end of the 0° polarizer 4 , and the second measuring probe 602 is connected to the output end of the 90° polarizer 5 .

The feature of the polarization-maintaining self-focusing lens 702 in the demodulation interferometer module 7 is that it can work on both the fast axis and the slow axis of the polarization-maintaining optical fiber; it can simultaneously realize internal surface reflection and transmission, and the light reflectivity of the lens is between 20% and Between 80%. The light collected by the first measurement probe 601 and the second test probe 602 is respectively input into the input end 7b of the polarization maintaining coupler 701 through the output end 3b of the polarization maintaining coupler 3, and the output end 7c of the polarization maintaining coupler 701 is connected to the polarization maintaining coupler 701. The self-focusing lens 702 is connected, and the output end 7a of the polarization maintaining coupler 701 is connected with the input end of the polarization beam splitter prism 803 . The polarization-maintaining self-focusing lens 702, the movable single-sided mirror 703 and the demodulation interferometer coupler 701 together form a demodulation interferometer. The scanning range L of the table top of the position scanning device 704 can satisfy that when the film thickness measurement probe module is not inserted into the film 603 to be measured, the demodulation interferometer can realize the optical path matching of the reflected light from the inner and outer surfaces of different probe lenses.

The output ends 8e and 8f of the polarization beam splitter prism 803 in the polarization beam splitting module 8 are respectively connected to the input ends of the second wavelength division multiplexer 801 and the third wavelength division multiplexer 802.

In the collection and control module 9, the first photodetector 903 is connected with the 8a output end of the second wavelength division multiplexer 801; the second photodetector 904 is connected with the 8b output end of the second wavelength division multiplexer 801; the third The photodetector 905 is connected to the 8c output end of the third wavelength division multiplexer 802 ; the fourth photodetector 906 is connected to the 8d output end of the third wavelength division multiplexer 802 . The photodetector transmits the collected signal to the computer 901 through the data acquisition card 902, and the computer 901 is also responsible for driving the position scanning device 704 to complete the optical path scanning.

The requirements for connecting optical fibers in the optical path are: the pigtail at the output end of the broadband light source 101, the narrow-band frequency-stabilized laser light source 103, the pigtails at each port of the first isolator 102, the pigtails at 104 ports of the second isolator, and the first wavelength division multiplexing The pigtails at each port of the device 105 are single-mode fibers; the pigtails at the output end of the 45° polarizer 2, the pigtails at each port of the polarization maintaining coupler 3, the pigtails at the input and output ends of the 0° analyzer 4, and the 90° analyzer 5 Pigtails at input and output ends, first measuring probe 601 pigtails, second measuring probe 602 pigtails, polarization maintaining coupler 701 pigtails at each port, polarization maintaining self-focusing lens 702 pigtails, polarization splitting prism 803 each port pigtails , Pigtails for each port of the second wavelength division multiplexer 801, pigtails for each port of the third wavelength division multiplexer 802, pigtails for the first photodetector 903, pigtails for the second photodetector 904, and pigtails for the third photodetector 905 Both the pigtail and the sixth photodetector 906 pigtail are polarization-maintaining fibers.

Optical interferometry is currently the most accurate distance measurement method. However, due to the long coherence length of the laser light source, laser interferometry can only achieve high-precision measurement of relative changes, but cannot achieve absolute measurement. White-light interferometry methods use low-coherence, broad-spectrum light sources. Since the coherence length of the low-coherence light source is very small, the shape of the output interference fringe after interference is a sinusoidal oscillation modulated by a Gaussian envelope. The fringe has a main maximum value, which corresponds to zero optical path difference between the two arms of the interferometer. s position. Due to the strict requirements on the optical path difference between the two arms of the interferometer, the position of the central fringe provides a high-quality reference position for the measurement of physical quantities. Therefore, the measurement of the physical quantity in the white light interferometry system is transformed into the measurement of the position change of the central fringe of the interference signal. The present invention adopts the design of dual light sources, as shown in Figure 5, during the scanning process of the position scanning device, the white light interference signal and the laser interference signal are recorded simultaneously, and by reading the number of fringes of the laser interference signal, the position of the position scanning device can be Move the actual distance for high-precision calibration.

As shown in Figure 2, when the film 603 to be tested is not inserted, the first measurement probe 601 returns light to measure the distance between the two probes as an example to illustrate the distance measurement method used in the present invention:

The internal reflected light 611 of the first measurement probe 601 and the external surface reflected light 612 of the second measurement probe 602 are divided into two paths by the first demodulation interferometer coupler: one path enters the first self-focusing lens 602 to generate 611' and 612' Reflected light; all the way into the first Faraday reflector 603 to generate 611" and 612" reflected light. Under the control of the computer 901, the position scanning device 704 drives the movable single-sided mirror 703 to scan the optical path, as shown in Figure 6, the process of generating the white light interference signal is:

(1) When the optical path difference between the two arms is equal to H, the light 611' in the scanning arm matches the light 612" in the fixed arm, and the first maximum white light interference signal 631 is generated.

(2) When the optical path difference between the two arms is equal to 0, in the scanning arm and the fixed arm, the light 611' and the light 611", and the light 612' and the light 612" are matched, and the main maximum white light interference signal 632 is generated.

(3) When the optical path difference between the two arms is equal to -H, the light 612' in the scanning arm matches the light 612" in the fixed arm, and the second maximum white light interference signal 633 is generated.

(4) The position extraction of the main maximum and sub-maximum envelopes is realized by performing Hilbert transform on the white light interference signal, and the absolute difference of the scanning distance between the main maximum and the sub-maximum is obtained by using the traceability characteristics of the laser interference signal value, which represents the absolute distance between the first measuring probe 601 and the second measuring probe 602 .

The film thickness measurement method based on the above white light interferometry method is:

(1) When the film 603 to be tested is not inserted, the optical path position scanning device 704 is driven to scan the optical path, and the internal reflected light 611 of the first measuring probe 601 is matched with the reflected light 612 on the outer surface of the second measuring probe 602 respectively. , The internal reflected light 621 of the second measurement probe 602 and the external surface reflected light 622 of the first measurement probe 601 perform optical path matching. The acquisition and control module 9 demodulates and records the relevant parameters to obtain the absolute distance H between the two measuring probes.

(2) Insert the film 603 to be measured into the middle of the first measuring probe 601 and the second measuring probe 602, and meet the requirement that the film 603 to be measured is perpendicular to the outgoing rays of the first measuring probe 601 and the second measuring probe 602. Drive the optical path position scanning device 704 to scan the optical path, respectively make the optical path match between the internal reflected light 613 of the first measuring probe 601 and the reflected light 614 on the front surface 603a of the film to be measured, and the internal reflected light 623 of the second measuring probe 602 and the light to be measured The light 624 reflected from the rear surface 603b of the measuring film is used for optical path matching. The relevant parameters are demodulated and recorded by the acquisition and control module 9, and the absolute distances H1 and H2 between the two measuring probes and the two surfaces of the film are respectively obtained.

(3) The film thickness d can be determined by the above two measured values, namely d=H-(H1+H2).

The following examples describe the present invention in more detail.

The present invention adopts the structure of dual light sources and common optical path to complete the research on high-precision measurement and traceability of film thickness, and the overall technical scheme is shown in Figure 1. The light source output module 1 is composed of a wide-spectrum light source 101 with a central wavelength of 1310nm, a narrow-band frequency-stabilized laser light source 103 with a wavelength of 1550nm, a first isolator 102 with a working wavelength of 1310nm, a second isolator 104 with a working wavelength of 1550nm, and a working wavelength of 1550nm. The 1310nm and 1550nm first wavelength division multiplexers 105 are jointly composed. Among them, the wide-spectrum light source 101 with a central wavelength of 1310nm is used as a measuring beam, mainly used to realize the absolute measurement of film thickness; the narrow-band frequency-stabilized laser light source 103 with a wavelength of 1550nm is used as an optical path correction beam, mainly used to realize traceability of film thickness measurement. The 1st isolator 102 and the 2nd isolator 104 enter into the 1st wavelength division multiplexer 105 and synthesize one beam and enter into the polarization maintaining coupler 3 that the light splitting ratio is 3dB after passing through the 45 ° polarizer 2, they are divided into two equally The path respectively passes through the 0° analyzer 4 and the 90° analyzer 5 and enters the film thickness measurement probe module 6; the ratio of the reflectivity to the transmittance of the lens end face of the first measurement probe 601 and the second measurement probe 602 is 50:50 ; The measuring light returned from the 1st measuring probe 601 and the 2nd measuring probe 602 is input into the polarization maintaining coupler 3 with a splitting ratio of 3dB through 0 ° polarizer 4 and 90 ° polarizer 5 respectively, and then by The polarization maintaining coupler 3 with a splitting ratio of 3dB is sent to the demodulation interferometer module 7 . The optical path matching is realized by the scanning of the position scanning device 704 in the demodulation interferometer module 7, and the return light of the two probes interferes at the polarization maintaining coupler 701 with a splitting ratio of 3dB. The interfered light is delivered to the polarization beam splitter 803 by the polarization maintaining coupler 701 with a splitting ratio of 3dB, so as to separate the beams of different polarization states collected by different probes. Connect the output end of the polarizing beam splitter prism 803 to the second wavelength division multiplexer 801 and the third wavelength division multiplexer 802 to separate the white light measurement beam with a center wavelength of 1310nm and the laser correction beam with a wavelength of 1550nm to be separated by the first photoelectric detector 903, second photodetector 904, third photodetector 905, and fourth photodetector 906. The photodetector transmits the collected signal to the computer 901 through the data acquisition card 902 for demodulation processing, and the computer 901 is responsible for driving the position scanning device 704 at the same time.

When the film 603 to be tested is not inserted, the output light of the light source output module 1 is split by the polarization maintaining coupler 3 with a splitting ratio of 3dB, and the light passes through the 0° analyzer 4 and the 90° analyzer 5 and enters the first Measuring probe 601 and second measuring probe 602 . As shown in Figure 2, the reflected light beam 611 by the inner surface of the lens of the first measuring probe 601 and the reflected light beam 612 on the outer surface of the lens of the second measuring probe 602 pass through the 0° analyzer 4; The light beam 621 and the light beam 622 reflected by the outer surface of the lens of the first measuring probe 601 pass through the 90° analyzer 5 . The above light beams are sent to the polarization maintaining coupler 3 with a splitting ratio of 3dB, and then sent to the demodulation interferometer module 7 by the polarization maintaining coupler 3 with a splitting ratio of 3dB. The ratio of light transmittance to light reflectance of the polarization-maintaining self-focusing lens 702 in the interferometer module 7 is 50:50. The transmission mode of the light beam in the demodulation interferometer module 7 is as follows: the return light of the film thickness measurement probe module 4 is input into the polarization-maintaining self-focusing lens 702 by the polarization-maintaining coupler 7 with a splitting ratio of 3dB, and the light beams are respectively in the polarization-maintaining self-focusing The inner surface of the lens 702 and the surface of the movable single-sided reflector 703 reflect respectively; when the position scanning device 704 scans the optical path, it drives the movable single-sided reflector 703 to move, so that the reflected light of the two film thickness measuring probes respectively Exact match of optical path. The light after interference is sent to the polarization beam splitter 803 to separate the beams of different polarization states collected by different probes, and the interference light after polarization separation is separated by the second wavelength division multiplexer 801 and the third wavelength division multiplexer 802 respectively. The white light measurement beam with a center wavelength of 1310nm and the laser calibration beam with a wavelength of 1550nm are separated from the two interference signals. White light interference fringes will be formed on the first photodetector 903 and the third photodetector 905, laser interference fringes will be formed on the second photodetector 904 and the fourth photodetector 906, and the white light interference signal can be demodulated Obtain the absolute distance H between the two measuring probes.

When the film 603 to be tested is inserted, the output light of the light source output module 1 is split by the polarization maintaining coupler 3 with a splitting ratio of 3dB, and the light passes through the 0° polarizer 4 and the 90° polarizer 5 respectively and enters the first measurement The probe 601 and the second measuring probe 602. As shown in Figure 3, the reflected light beam 613 on the inner surface of the first measurement probe 601 lens and the reflected light beam 614 on the front surface 603a of the film to be measured pass through the 0° analyzer 4; The light beam 624 reflected by the rear surface 603b of the film passes through the 90° analyzer 5 . The above light beams are sent to the polarization maintaining coupler 3 with a splitting ratio of 3dB, and then sent to the demodulation interferometer module 7 by the polarization maintaining coupler 3 with a splitting ratio of 3dB. The transmission mode of the light beam in the demodulation interferometer module 7 is as follows: the return light of the film thickness measurement probe module 4 is input into the polarization-maintaining self-focusing lens 702 by the polarization-maintaining coupler 7 with a splitting ratio of 3dB, and the light beams are respectively in the polarization-maintaining self-focusing The inner surface of the lens 702 and the surface of the movable single-sided reflector 703 reflect respectively; when the position scanning device 704 scans the optical path, it drives the movable single-sided reflector 703 to move, so that the reflected light of the two film thickness measuring probes respectively Exact match of optical path. The light after interference is sent to the polarization beam splitter 803 to separate the beams of different polarization states collected by different probes, and the interference light after polarization separation is separated by the second wavelength division multiplexer 801 and the third wavelength division multiplexer 802 respectively. The white light measurement beam with a center wavelength of 1310nm and the laser correction beam with a wavelength of 1550nm are separated from the two interference signals. White light interference fringes will be formed on the first photodetector 903 and the third photodetector 905; laser interference fringes will be formed on the second photodetector 904 and the fourth photodetector 906. By demodulating the white light interference signal, The distance H1 of the first measuring probe 601 to the front surface 603a of the film to be tested, and the distance H2 of the second measuring probe 602 to the front surface 603b of the film to be tested are respectively obtained.

Therefore, the film thickness is determined by the above two measured values, ie H-(H1+H2).

Claims (7)

1. A polarization multiplexing common optical path self-calibration film thickness measurement device, including a light source output module (1), a film thickness measurement probe module (6), a demodulation interferometer module (7), and a polarization beam splitter module (8) And collection and control module (9); It is characterized in that: the output light of light source output module (1) is input in the polarization maintaining coupler (3) through 45 ° polarizer (2); The polarization maintaining coupler (3) will The incident light is divided into two paths and enters the first measuring probe (601) and the second measuring probe (602) of the film thickness measuring probe module (6) through the 0° polarizer (4) and the 90° polarizer (5) respectively The measurement is carried out in the middle; the return light via the first measuring probe (601) and the second measuring probe (602) is input in the demodulation interferometer module (7); through the position scanning device ( The scanning of 704) realizes the matching of optical path; Input the interference signal of matching optical path into the polarization beam splitting module (8) to realize the separation of different polarization states and different wavelengths of interference light; the separated interference signal is collected and controlled by the module ( 9) to collect and calculate related parameters. 2. The polarization multiplexed common optical path self-calibration film thickness measurement device according to claim 1, characterized in that: the light source output module (1) consists of a wide-spectrum light source (101), a first isolator (102), Composed of a narrowband frequency-stabilized laser light source (103), a second isolator (104) and a first wavelength division multiplexer (105), the broadband light source (101) is connected to the first isolator (102), and the narrowband frequency stabilizer The laser light source (103) is connected to the input end of the second isolator (104), and the output end of the first isolator (102) and the second isolator (104) are respectively connected to the first input of the first wavelength division multiplexer (105). Terminal (1a) and the second input terminal (1b) are connected. 3. The common optical path self-calibration film thickness measuring device of polarization multiplexing according to claim 2, is characterized in that: each light source in the described light source output module (1) is characterized by: half of the wide-spectrum light source (101) The spectral width is greater than 45nm, and the fiber output power is greater than 2mW; the half-spectrum width of the narrow-band frequency-stabilized laser light source (103) is less than 1pm, and the fiber output power is greater than 2mW; the wide-spectrum light source (101) and the narrow-band frequency-stabilized laser light source (103) have different The central wavelength, and the spectrum of the two has no overlapping part within the half-spectrum width. 4. A kind of polarization multiplexing common optical path self-calibration film thickness measuring device according to claim 1, characterized in that: the film thickness measuring probe (6) is composed of a first measuring probe (601) and a second measuring probe (602); the first measuring probe (601) and the second measuring probe (602) can realize the transmission and reflection of the transmitted light at the same time; the first measuring probe (601) and the second measuring probe (602) maintain the polarization Both the fast axis and the slow axis of the optical fiber can work; the outgoing rays of the first measuring probe (601) and the second measuring probe (602) coincide with each other; ) and the outgoing light of the second measuring probe (602) are vertical; the first measuring probe (601) is connected to the output end of the 0° polarizer (4), and the second measuring probe (602) is connected to the 90° polarizer ( 5) The output terminals are connected. 5. The common optical path self-calibration film thickness measurement device of polarization multiplexing according to claim 1, characterized in that: the demodulation interferometer module (7) consists of a polarization maintaining coupler (701), a polarization maintaining self-focusing lens (702), a movable single-sided mirror (703) and a position scanning device (704), the polarization-maintaining self-focusing lens (702) can work on both the fast axis and the slow axis of the polarization-maintaining optical fiber, and can simultaneously realize reflection and The light reflectivity of transmission and lens is between 20%～80%. The light collected by the first measurement probe (601) and the second test probe (602) passes through the second output end ( 3b) input to the second input terminal (7b) of the polarization maintaining coupler (701), the third output terminal (7c) of the polarization maintaining coupler (701) is connected with the polarization maintaining self-focusing lens (702), and the polarization maintaining coupler The first output end (7a) of (701) is connected with the input end of polarization splitter prism (803); Polarization-maintaining self-focusing lens (702), movable single-sided mirror (703) and demodulation interferometer coupler (701 ) together form a demodulation interferometer. 6. The common optical path self-calibration film thickness measurement device of polarization multiplexing according to any one of claims 1-5, is characterized in that the optical path is connected with the characteristics of optical fiber: wide-spectrum light source (101) output end pigtail, narrowband Frequency-stabilized laser light source (103), pigtails at each port of the first isolator (102), pigtails at each port of the second isolator (104), first wavelength division multiplexer (105), 45° polarizers (2 ) The pigtails at the input end and the pigtails at each port are single-mode fibers; the 45° polarizer (2) the output end pigtails, the polarization maintaining coupler (3) the pigtails at each port, and the 0° polarizer (4) input and output end fiber pigtail, 90° analyzer (5) input and output pigtail fiber, the first measuring probe (601) pigtail, the second measuring probe (602) pigtail, the polarization maintaining coupler (701) each port pigtail, Polarization maintaining self-focusing lens (702) pigtail, polarization beam splitter (803) each port pigtail, second wavelength division multiplexer (801) each port pigtail, third wavelength division multiplexer (802) each port tail The first photodetector (903) pigtail, the second photodetector (904) pigtail, the third photodetector (905) pigtail, and the sixth photodetector (906) pigtail are all polarization-maintaining fibers. 7. A film thickness measurement method based on the common optical path self-calibration film thickness measurement device of polarization multiplexing according to claim 1, characterized in that: (1), when the film to be measured (603) is not inserted, drive the optical path position scanning device (704) to perform optical path scanning, so that the internal reflection light (611) of the first measuring probe (601) and the second measuring probe (602) ) external surface reflected light (612) for optical path matching, the second measuring probe (602) internal reflected light (621) and the first measuring probe (601) external surface reflected light (622) for optical path matching; through acquisition and control Module (9) demodulates and records, and obtains the absolute distance H between the two measuring probes; (2), Insert the film to be measured (603) into the middle of the first measuring probe (601) and the second measuring probe (602), the film to be measured (603) and the first measuring probe (601) and the second measuring probe (602) ) is vertical; the optical path position scanning device (704) is driven to scan the optical path, so that the reflected light (613) inside the first measuring probe (601) and the reflected light (614) from the front surface of the film to be measured (603a) are Optical path matching, the optical path matching of the internal reflected light (623) of the second measuring probe (602) and the reflected light (624) of the back surface of the film to be tested (603b); demodulation of relevant parameters through the acquisition and control module (9) Record, respectively obtain the distance H1 of the first measuring probe (601) of the film to be measured front surface (603a), and the distance H2 of the second measuring probe (602) of the film to be measured front surface (603b); (3) Determine the film thickness d from the above two measured values, ie d=H-(H1+H2).