CN114562943A - Measuring system and measuring method - Google Patents

Measuring system and measuring method Download PDF

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Publication number
CN114562943A
CN114562943A CN202011354760.4A CN202011354760A CN114562943A CN 114562943 A CN114562943 A CN 114562943A CN 202011354760 A CN202011354760 A CN 202011354760A CN 114562943 A CN114562943 A CN 114562943A
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China
Prior art keywords
light
signal
optical switch
optical
detected
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陈鲁
白园园
马砚忠
张嵩
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Shenzhen Zhongke Feice Technology Co Ltd
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Shenzhen Zhongke Feice Technology Co Ltd
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Priority to CN202011354760.4A priority Critical patent/CN114562943A/en
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    • G—PHYSICS
    • 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
    • G01B11/0625—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 with measurement of absorption or reflection

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  • General Physics & Mathematics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)

Abstract

The invention provides a measuring system and a measuring method, comprising a light emitting module, a modulation module and a detection module, wherein the light emitting module is used for generating first pumping light and detection light; the modulation module comprises: a first light splitting assembly for splitting the first pump light into a first beam and a second beam; the optical switch is used for controlling the on-off of the optical path of the first light beam and/or the optical path of the second light beam; the beam combining component is used for combining the first light beam and the second light beam which pass through the optical splitting light to form second pump light which is irradiated to the surface of an object to be detected to form sound waves in the object to be detected, and the probe light is reflected to form signal light after reaching the surface of the object to be detected; the detection module is used for detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light. Compared with the prior art, the modulation mode in the invention can enable the modulation depth of the pump light to reach 100%, thereby improving the signal-to-noise ratio of the pump light signal and improving the measurement precision of the object to be measured.

Description

Measuring system and measuring method
Technical Field
The present invention relates to the field of optical measurement technologies, and more particularly, to a measurement system and a measurement method.
Background
With the development of modern technologies, the size of semiconductor chips is decreasing, and the processing technology of semiconductor chips is updating. However, since the number of processing steps of a semiconductor chip is large, and a chip produced in any processing step is unqualified, which may cause the whole chip to fail, in the prior art, a detection procedure is often introduced after a key processing step, and the unqualified chip is removed in time by detecting information such as the film thickness of the chip, thereby improving the yield of the chip product.
The existing method for measuring the thickness of the metal film is a measuring method based on a photoacoustic effect and a pumping detection technology, wherein pumping light is used for inducing the film to be measured to generate sound waves, the reflectivity of the detection light irradiated on the film to be measured is changed by changing the optical characteristics of the material of the film to be measured through the sound waves, and the thickness of the film to be measured can be calculated according to the time when the emissivity is changed and the propagation speed of the sound waves in the film to be measured.
However, before the pump light is irradiated onto the surface of the object, the pump light needs to be modulated. In the prior art, the intensity of the pump light is modulated, but the modulation depth of the pump light is often less than 100%, so that the signal-to-noise ratio of a pump light signal is influenced, and the measurement accuracy of the thickness of a film to be measured is influenced.
Disclosure of Invention
In view of this, the present invention provides a measurement system and a measurement method to improve the modulation depth of the pump light and improve the signal-to-noise ratio of the pump light signal.
In order to achieve the purpose, the invention provides the following technical scheme:
a measurement system, comprising:
the optical transmitting module is used for generating first pumping light and probe light;
the modulation module is used for modulating the first pump light to form second pump light which irradiates the surface of an object to be detected, acoustic waves are formed in the object to be detected, and the probe light is reflected to form signal light after reaching the surface of the object to be detected;
the modulation module includes: a first optical splitting assembly for splitting the first pump light into a first beam and a second beam, the first and second beams having different optical properties; the optical switch is used for controlling the on-off of the optical path of the first light beam and/or the optical path of the second light beam; the beam combining assembly is used for combining the first beam and the second beam of the split light to form second pump light;
and the detection module is used for detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light.
Optionally, the first light splitting component comprises a polarizing beam splitter or an amplitude beam splitter; the polarization beam splitter is used for enabling the first light beam and the second light beam to have different polarization states; the amplitude beam splitter is configured to cause the first beam and the second beam to have different amplitudes.
Optionally, the optical switch alternately switches the optical path of the first light beam and the optical path of the second light beam.
Optionally, the optical switch comprises one or a combination of a first optical switch and a second optical switch;
the first optical switch is used for controlling the on-off of the optical path of the first light beam;
the second optical switch is used for controlling the on-off of the optical path of the second light beam.
Optionally, the modulation module further includes a radio frequency control unit, and the radio frequency control unit is connected to the optical switch;
the radio frequency control unit is used for outputting a control signal to the optical switch, so that the on or off state of the optical switch is controlled through the control signal, and the on or off state of the first light beam and/or the on or off state of the second light beam is controlled through controlling the on or off state of the optical switch.
Optionally, the modulation module further includes a signal generation unit, and the signal generation unit is connected to the radio frequency control unit;
the signal generating unit is used for inputting a parameter control signal to the radio frequency control unit so as to control the radio frequency control unit to output the control signal.
Optionally, the optical switch includes a first optical switch and a second optical switch, the radio frequency control unit includes a first sub-control unit and a second sub-control unit, the first sub-control unit is configured to generate a first control signal according to the parameter control signal and output the first control signal to the first optical switch, and the second sub-control unit is configured to generate a second control signal according to the parameter control signal and output the second control signal to the second optical switch, so as to control an on or off state of the first optical switch by the first control signal and control an on or off state of the second optical switch by the second control signal; the parameter control signal comprises square waves, and the duty ratio of the parameter control signal is 40% -60%.
Optionally, the detection module comprises a detector, a demodulator and a data processing module;
the detector is used for detecting signal light formed when the detection light and the pump light have different delay times and obtaining a detection signal of the change of the light intensity of the signal light along with the delay time;
the demodulator is used for receiving a reference signal output by the signal generating unit and a detection signal of the light intensity of the signal light output by the detector along with the change of delay time, demodulating the detection signal according to the reference signal and transmitting the demodulated detection signal to the data processing module;
and the data processing module is used for obtaining the detection information of the object to be detected according to the demodulated detection signal.
Optionally, the light emitting module comprises:
a laser for generating laser light;
a second light splitting component for splitting the laser light into the first pump light and the probe light;
a time delayer for adjusting a delay time between the probe light and the first pump light or adjusting a delay time between the probe light and the second pump light.
Optionally, the optical switch comprises an acousto-optic modulator.
Optionally, the first pump light includes pulsed light, and the probe light is pulsed light or continuous light.
Optionally, the detection information includes one or a combination of a film thickness, a sound velocity in the test object, or a modulus of elasticity of the test object.
A measurement method applied to the measurement system as described in any one of the above, the measurement method comprising:
generating first pump light and probe light;
splitting the first pump light into a first beam and a second beam, the first and second beams having different optical properties;
controlling the on-off of the light path of the first light beam and/or the light path of the second light beam through an optical switch, combining the first light beam and the second light beam which are split by light to form second pump light which is irradiated to the surface of an object to be detected to form sound waves in the object to be detected, and reflecting the probe light to form signal light after reaching the surface of the object to be detected;
and detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light.
Optionally, splitting the first pump light into a first beam and a second beam comprises:
splitting the first pump light into a first beam and a second beam having different polarization states;
alternatively, the first pump light is split into a first beam and a second beam having different amplitudes.
Optionally, controlling the on/off of the optical path of the first light beam and/or the optical path of the second light beam by an optical switch comprises:
and controlling the light path of the first light beam and the light path of the second light beam to be alternately switched on and off through an optical switch.
Optionally, detecting the signal light, and obtaining the to-be-detected information of the object to be detected according to the signal light includes:
detecting signal light formed when the detection light and the pump light have different delay times, and obtaining a detection signal of which the light intensity of the signal light changes along with the delay time;
and demodulating the detection signal, and acquiring the detection information of the object to be detected according to the demodulated detection signal.
Compared with the prior art, the technical scheme provided by the invention has the following advantages:
the measuring system and the measuring method provided by the invention have the advantages that the first pump light is divided into the first light beam and the second light beam, the first light beam and the second light beam have different optical properties, the on-off of the light path of the first light beam and/or the light path of the second light beam is controlled through the optical switch, the first light beam and the second light beam which pass through the optical switch are combined through the beam combining component to form the second pump light, the second pump light has different optical properties, and the modulation of the first pump light is realized. Compared with the method for modulating the pump light in the prior art, the modulation method in the invention can enable the modulation depth of the pump light to reach 100%, thereby improving the signal-to-noise ratio of the pump light signal and improving the measurement precision of the object to be measured.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a measurement system according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
FIG. 4 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
FIG. 5 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
FIG. 6 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
FIG. 7 is a schematic structural diagram of a measurement system according to another embodiment of the present invention;
fig. 8 is a flowchart of a measurement method according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, so that the above is the core idea of the present invention, and the above objects, features and advantages of the present invention can be more clearly understood. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the present invention provides a measurement system, as shown in fig. 1, including:
an optical emitting module 10 for generating a first pump light B1 and a probe light T;
the modulation module 11 is configured to modulate the first pump light B1 to form a second pump light B2, irradiate the second pump light B2 onto the surface of the object a to be detected, form an acoustic wave in the object a to be detected, and reflect the probe light T after reaching the surface of the object a to be detected to form a signal light X;
and the detection module 12 is configured to detect the signal light X and obtain information to be detected of the object to be detected a according to the signal light X.
The modulation module 11 includes a first light splitting component 110, an optical switch 111, and a beam combining component 112, where the first light splitting component 110 is configured to split the first pump light B1 into a first light beam S1 and a second light beam S2, and the first light beam S1 and the second light beam S2 have different optical properties; the optical switch 111 is used for controlling the on-off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2; the beam combining module 112 is configured to combine the first beam S1 and the second beam S2 passing through the split light 111 to form a second pump light B2.
In the embodiment of the present invention, the first pump light B1 is divided into the first light beam S1 and the second light beam S2, because the first light beam S1 and the second light beam S2 have different optical properties, the optical switch 111 controls the on/off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2, the beam combining component 112 combines the first light beam S1 and the second light beam S2 passing through the light splitting light 111 to form the second pump light B2, so that the second pump light B2 has different optical properties, and the modulation of the first pump light B1 is realized. Compared with the method for modulating the pump light in the prior art, the modulation method in the embodiment of the invention can enable the modulation depth of the pump light to reach 100%, thereby improving the signal-to-noise ratio of the pump light signal and improving the measurement precision of the object to be measured.
It should be noted that, as shown in fig. 1, the light spot formed on the surface of the object a by the second pump light B2 and the probe light T at least partially coincides, an incident angle of the second pump light B2 incident on the object a is different from an incident angle of the probe light T incident on the object a, and optionally, the probe light T perpendicularly enters the surface of the object a.
In some embodiments of the present invention, the first light beam S1 and the second light beam S2 having different optical properties include the first light beam S1 and the second light beam S2 having different polarization states. In this embodiment, the first beam splitting assembly 110 includes a polarization beam splitter, and the beam combining assembly 112 includes a polarization coupler.
Among them, the polarization beam splitter is used to make the first beam S1 and the second beam S2 have different polarization states, that is, the polarization beam splitter is used to split the first pump light B1 into the first beam S1 and the second beam S2, and make the first beam S1 and the second beam S2 have different polarization states. The first pump light B1 is linearly polarized light, and the first light beam S1 and the second light beam S2 are linearly polarized light; the polarization direction of the first pump light B1 and the polarization direction of the first light beam S1 both have a non-zero included angle, and the polarization direction of the first pump light B1 and the polarization direction of the second light beam S2 both have a non-zero included angle. Alternatively, the polarization states of the first light beam S1 and the second light beam S2 are perpendicular, for example, the first light beam S1 is P-polarized light, the second light beam S2 is S-polarized light, or the first light beam S1 is S-polarized light, the second light beam S2 is P-polarized light, etc.
The optical switch 111 is used to control the on/off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2. Alternatively, the optical switch 111 is used to alternately switch the optical path of the first light beam S1 and the optical path of the second light beam S2. For example, during the first time period, the optical path of the first light beam S1 is controlled to be on, the optical path of the second light beam S2 is controlled to be off, and only the first light beam S1 is transmitted to the beam combining element 112, during the second time period, the optical path of the first light beam S1 is controlled to be off, and the optical path of the second light beam S2 is controlled to be on, and only the second light beam S2 is transmitted to the beam combining element 112.
The beam combining component 112, i.e. the polarization coupler, is used to combine the first beam S1 and the second beam S2 with different polarization states to form the second pump light B2. Because the optical switch 111 controls the on/off of the optical path of the first optical beam S1 and/or the optical path of the second optical beam S2, the optical beams transmitted to the beam combining component 112 in at least two different time periods can have different polarization states, so that the second pump light B2 output after being combined by the beam combining component 112 has different polarization states in at least two different time periods, that is, the second pump light B2 has different polarization states, thereby realizing polarization modulation of the pump light, that is, the first pump light B1.
Of course, the invention is not so limited and in another embodiment, the first light beam S1 and the second light beam S2 have different optical properties including the first light beam S1 and the second light beam S2 having different amplitudes. In this case, the first light splitting assembly 110 includes an amplitude beam splitter, and the beam combining assembly 112 includes an amplitude coupler.
Wherein the amplitude beam splitter is used to make the first beam S1 and the second beam S2 have different amplitudes, i.e., the amplitude beam splitter is used to split the first pump light B1 into the first beam S1 and the second beam S2, and to make the first beam S1 and the second beam S2 have different amplitudes.
The optical switch 111 is used for controlling the on/off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2. Alternatively, the optical switch 111 is used to alternately switch the optical path of the first light beam S1 and the optical path of the second light beam S2. For example, during the first time period, the optical path of the first light beam S1 is controlled to be on, the optical path of the second light beam S2 is controlled to be off, and only the first light beam S1 is transmitted to the beam combining element 112, during the second time period, the optical path of the first light beam S1 is controlled to be off, and the optical path of the second light beam S2 is controlled to be on, and only the second light beam S2 is transmitted to the beam combining element 112.
The beam combining component 112, i.e. the amplitude coupler, is used to combine the first beam S1 and the second beam S2 with different amplitudes to form the second pump beam B2. Since the optical switch 111 controls the on/off of the optical path of the first optical beam S1 and/or the optical path of the second optical beam S2, the optical beams transmitted to the beam combining component 112 in at least two different time periods can have different amplitudes, and therefore, the second pump light B2 output after being combined by the beam combining component 112 has different amplitudes in at least two different time periods, even though the second pump light B2 has different amplitudes, and thus the modulation of the amplitude of the pump light, that is, the first pump light B1 is realized. Of course, in other embodiments of the present invention, other optical properties of the pump light may also be modulated, which is not described in detail herein.
The amplitude modulation mode in the embodiment of the invention can enable the modulation depth of the pump light, namely the first pump light B1, to reach 100%, further improve the signal-to-noise ratio of the pump light, namely the first pump light B1 signal, and improve the measurement accuracy of the object A to be measured.
It should be noted that, in the embodiment of the present invention, the optical switch 111 may control the on/off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2 according to actual conditions. Based on this, in some embodiments of the present invention, the optical switch 111 comprises one or a combination of the first optical switch 1111 and the second optical switch 1112, that is, the optical switch 111 comprises the first optical switch 1111 and/or the second optical switch 1112, wherein the first optical switch 1111 is used for controlling on/off of the optical path of the first light beam S1, and the second optical switch 1112 is used for controlling on/off of the optical path of the second light beam S2.
In some embodiments of the present invention, as shown in fig. 2, the optical switch 111 only includes the first optical switch 1111, that is, the optical switch 111 only controls the on/off of the optical path of the first light beam S1, and the optical path of the second light beam S2 is continuously on. The first optical switch 1111 controls on/off of the optical path of the first optical beam S1, so that the second pump light B1 combined by the beam combining component 112 has different optical properties in at least two time periods, that is, the second pump light B1 has different optical properties, and modulation of the first pump light B1 is realized.
In other embodiments of the present invention, as shown in fig. 3, the optical switch 111 only includes the second optical switch 1112, that is, the optical switch 111 only controls the on/off of the optical path of the second light beam S2, and the optical path of the first light beam S1 is continuously on. The second optical switch 1112 controls on/off of the optical path of the second optical beam S2, so that the second pump light B1 combined by the beam combining component 112 has different optical properties in at least two time periods, that is, the second pump light B1 has different optical properties, and modulation of the first pump light B1 is achieved.
In other embodiments of the present invention, as shown in fig. 4, the optical switch 111 includes a first optical switch 1111 and a second optical switch 1112, that is, the optical switch 111 controls the on/off of the optical paths of the first light beam S1 and the second light beam S2. The first optical switch 1111 and the second optical switch 1112 control the optical paths of the first light beam S1 and the second light beam S2 to be alternately switched on and off, so that the second pump light B1 after being combined by the beam combining component 112 has different optical properties in at least two time periods, that is, the second pump light B1 has different optical properties, and the modulation on the first pump light B1 is realized.
On the basis of the above embodiments, in some embodiments of the present invention, as shown in fig. 5, the modulation module 11 further includes a radio frequency control unit 113, and the radio frequency control unit 113 is connected to the optical switch 111, and is configured to output a control signal to the optical switch 111 to control an on or off state of the optical switch 111, so as to control an optical path of the first light beam S1 and/or an on or off state of an optical path of the second light beam S2 by controlling the on or off state of the optical switch 111.
If the optical switch 111 only includes the first optical switch 1111, the rf control unit 113 is connected to the first optical switch 1111 and configured to output a control signal to the first optical switch 1111 to control an on or off state of the first optical switch 1111. When the first optical switch 1111 is in the on state, the optical path of the first light beam S1 is in the on state, and when the first optical switch 1111 is in the off state, the optical path of the first light beam S1 is in the off state.
If the optical switch 111 only includes the second optical switch 1112, the rf control unit 113 is connected to the second optical switch 1112, and is configured to output a control signal to the second optical switch 1112 to control an on or off state of the second optical switch 1112. When the second optical switch 1112 is in an on state, the optical path of the second light beam S2 is in an on state, and when the second optical switch 1112 is in an off state, the optical path of the second light beam S2 is in an off state.
If the optical switch 111 includes a first optical switch 1111 and a second optical switch 1112, the rf control unit 113 includes a first sub-control unit and a second sub-control unit, the first sub-control unit is connected to the first optical switch 1111, the second sub-control unit is connected to the second optical switch 1112, the first sub-control unit is configured to output a first control signal to the first optical switch 1111, and the second sub-control unit is configured to output a second control signal to the second optical switch 1112, so as to control on or off states of the first optical switch 1111 and the second optical switch 1112. When the first control signal and the second control signal are different, the on or off states of the first optical switch 1111 and the second optical switch 1112 are different. Based on this, the first optical switch 1111 and the second optical switch 1112 can be controlled to be alternately turned on by the first control signal and the second control signal.
Also, when the first optical switch 1111 is in the on state, the optical path of the first light beam S1 is in the on state, and when the first optical switch 1111 is in the off state, the optical path of the first light beam S1 is in the off state. When the second optical switch 1112 is in the on state, the optical path of the second light beam S2 is in the on state, and when the second optical switch 1112 is in the off state, the optical path of the second light beam S2 is in the off state.
In some embodiments of the present invention, optical switch 111 comprises an acousto-optic modulator. The first optical switch 1111 includes an acousto-optic modulator, and the second optical switch 1112 also includes an acousto-optic modulator. Of course, the invention is not limited in this regard and other modulators or switches may be used as the optical switches in other embodiments.
On this basis, in some embodiments of the present invention, as shown in fig. 5, the modulation module 11 further includes a signal generating unit 114, the signal generating unit 114 is connected to the radio frequency control unit 113, and the signal generating unit 114 is configured to input a parameter control signal to the radio frequency control unit 113 so as to control the radio frequency control unit 113 to output a control signal. When the rf control unit 113 includes a first sub-control unit and a second sub-control unit, the first sub-control unit generates a first control signal according to the parameter control signal input by the signal generating unit 114 and transmits the first control signal to the first optical switch 1111, and the second sub-control unit generates a second control signal according to the parameter control signal input by the signal generating unit 114 and transmits the second control signal to the second optical switch 1112. The parameter control signal comprises square waves, the duty ratio of the parameter control signal is 40% -50%, and the preferred duty ratio is 50%.
In some embodiments of the present invention based on any of the above embodiments, as shown in fig. 6, the light emitting module 10 includes:
a laser 100 for generating laser light;
a second beam splitting module 101 for splitting the laser light into a first pump light B1 and a probe light T;
and a time delayer 102 for adjusting a delay time between the probe light T and the first pump light B1 or adjusting a delay time between the probe light T and the second pump light B2. Wherein the time delayer 102 is disposed on the optical path of the probe light T and configured to time-delay the probe light T, or the time delayer 102 is disposed on the optical path of the first pump light B1 and configured to time-delay the first pump light B1, or the time delayer 102 is disposed on the optical path of the second pump light B2 and configured to time-delay the second pump light B2.
Optionally, the second light splitting element 101 comprises a fiber optic splitter; the first pump light B1 is transmitted along the third optical fiber and the probe light T is transmitted along the fourth optical fiber. In other words, in the embodiment of the present invention, the optical path between any two devices may adopt an optical fiber, that is, the optical fiber is adopted to transmit the pump light and the probe light between the two devices, so as to further reduce the difficulty in adjusting the optical path of the measurement system, and improve the stability and the anti-interference capability of the system.
Of course, the present invention is not limited thereto, and in other embodiments, the light emitting module 10 may include a first light source for emitting the probe light T and a second light source for emitting the first pump light B1. Wherein, the first light source and the second light source comprise a laser, a light emitting diode and the like.
It should be noted that, in the embodiment of the present invention, the detection light T is continuous light or pulsed light; the first pump light B1 is pulsed light. When the probe light T and the first pump light B1 are obtained by splitting the same continuous light beam, the optical path of the first pump light B1 also has a light modulator for modulating the pump light B from the continuous light beam to the pulsed light.
Based on any of the above embodiments, in some embodiments of the present invention, as shown in fig. 7, the detection module 12 includes a detector 120, a data processing module 121, and a demodulator 122.
The detector 120 is configured to detect the signal light X formed when the probe light T and the pump light, that is, the first pump light B1 or the second pump light B2, have different delay times, and obtain a detection signal indicating that the light intensity of the signal light X changes with time;
the demodulator 122 is configured to receive the reference signal output by the signal emitting unit 114 in the optical transmitting module 10 and the detection signal of the light intensity of the signal light X output by the detector 120 varying with the delay time, demodulate the detection signal of the light intensity of the signal light X varying with the delay time according to the reference signal, and transmit the demodulated detection signal of the light intensity of the signal light X varying with the delay time to the data processing module 121. Wherein the demodulator 122 comprises a lock-in amplifier or a chopper.
The data processing module 121 is configured to obtain detection information of the object a according to the demodulated detection signal. The detection information comprises one or the combination of the thickness of the film layer, the sound velocity in the object to be detected or the elastic modulus of the object to be detected.
It should be noted that the frequency of the reference signal output by the signal transmitting unit 114 is the same as the frequency of the parameter control signal output by the signal transmitting unit 114, so as to demodulate the signal light X whose reflectivity changes under the action of the acoustic wave generated by the excitation of the second pump light B2 modulated according to the parameter control signal.
In some embodiments of the present invention, the data processing module 121 is configured to obtain a variation time period of the detection signal according to the detection signal that the light intensity of the signal light X varies with the delay time, and obtain the to-be-detected information of the object a to be detected according to the time period. The data processing module 121 is configured to obtain a time period according to a delay time difference between adjacent peak values or adjacent valley values of the detected signal.
In some embodiments of the present invention, the detection information includes a thickness of the object a to be measured, and the data processing module 121 is further configured to obtain the thickness of the object a to be measured according to the time period and the sound velocity. Or in other embodiments of the present invention, the detection information includes a sound velocity of the object a to be measured, and the data processing module 121 is further configured to obtain the sound velocity in the object a to be measured according to the time period and the thickness of the object a to be measured.
Since the time of the acoustic wave transmitted inside the object a is unknown, in the embodiment of the present invention, the delay time of the time delay device 102 is continuously adjusted, so that the delay times of the pump light, i.e., the first pump light B1 or the second pump light B2, and the probe light T are Δ T in sequence1、△t2、△t3… …, and Δ t1、△t2、△t3… … are sequentially increased, and then by detecting the signal light X, the light intensity of the signal light X at a plurality of delay times, that is, a detection signal in which the light intensity of the signal light X varies with the delay time, is obtained.
When the acoustic wave and the detection light T are transmitted to the surface of the object A to be detected simultaneously, the reflectivity change of the detection light T is the largest, namely the light intensity change of the detected signal light X is the largest, so that the time difference of the two adjacent acoustic waves transmitted to the upper surface of the object A to be detected can be obtained according to the time difference between the two points with the largest light intensity change, and the time of the acoustic waves transmitted between the two opposite surfaces of the object A to be detected can be obtained.
That is, the variation time period of the detection signal can be obtained according to the delay time difference between two adjacent light intensity peak values or the delay time difference between two adjacent light intensity valley values in the detection signal, and the variation time period is equal to the time difference between two adjacent sound waves propagating to the upper surface of the object a and the time between two opposite surfaces of the object a, so that the information to be detected of the object a can be obtained according to the variation time period of the detection signal.
The time of the acoustic wave propagating in the object a is the sum of the time of the acoustic wave generated from the surface of the object a reaching the interface between the object a and the substrate and the time of the acoustic wave reflected from the interface back to the surface of the object a. D is the thickness of the object a, V is the propagation speed of the acoustic wave in the object a, and T is the time for the acoustic wave to propagate in the object a, i.e. the change time period of the interference information.
An embodiment of the present invention further provides a measurement method, which is applied to the measurement system provided in any of the above embodiments, and as shown in fig. 8, the measurement method includes:
s101: generating first pump light and probe light;
referring to fig. 1, the optical transmission module generates first pump light B1 and probe light T.
In some embodiments of the present invention, referring to fig. 6, the optical transmission module 10 includes a laser 100 and a second light splitting assembly 101, wherein the laser 100 generates laser light; the second beam splitting module 101 splits the laser light into a first pump light B1 and a probe light T. Of course, the present invention is not limited thereto, and in another embodiment, the first pump light B1 and the probe light T may be generated by two light sources respectively. S102: splitting the first pump light into a first beam and a second beam, the first and second beams having different optical properties;
s103: controlling the on-off of the light path of the first light beam and/or the light path of the second light beam through the optical switch, combining the first light beam and the second light beam which pass through the optical switch to form second pump light which is irradiated to the surface of an object to be detected, forming sound waves in the object to be detected, and reflecting the probe light to form signal light after reaching the surface of the object to be detected;
referring to fig. 1, the modulation module 11 includes a first light splitting assembly 110, an optical switch 111, and a beam combining assembly 112, the first light splitting assembly 110 splits the first pump light B1 into a first light beam S1 and a second light beam S2, and the first light beam S1 and the second light beam S2 have different optical properties; the optical switch 111 controls the on-off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2; the beam combining assembly 112 combines the first beam S1 and the second beam S2 passing through the beam splitting assembly 111 to form a second pump beam B2 and irradiates the surface of the object a to be measured, so as to form an acoustic wave in the object a, and the probe beam T reaches the surface of the object a to be measured and then is reflected to form a signal beam X.
S104: and detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light.
Referring to fig. 1, after the detection light T reaches the surface of the object a to be detected and is reflected to form the signal light X, the detection module 12 detects the signal light X and obtains the information to be detected of the object a to be detected according to the signal light X.
In some embodiments of the present invention, splitting the first pump light B1 into the first beam S1 and the second beam S2 comprises:
splitting the first pump light B1 into a first beam S1 and a second beam S2 having different polarization states;
alternatively, the first pump light B1 is split into the first beam S1 and the second beam S2 having different amplitudes.
In some embodiments of the present invention, the first light beam S1 and the second light beam S2 having different optical properties include the first light beam S1 and the second light beam S2 having different polarization states. Based on this, the first pump light B1 can be split into the first light beam S1 and the second light beam S2 with different polarization states by the polarization beam splitter, and after the optical switch 111 controls the on/off of the optical path of the first light beam S1 and/or the optical path of the second light beam S2, the first light beam S1 and the second light beam S2 with different polarization states are combined by the polarization coupler to form the second pump light B2.
Of course, the invention is not limited in this regard and other embodiments of the invention in which the first light beam S1 and the second light beam S2 have different optical properties include the first light beam S1 and the second light beam S2 having different amplitudes. Based on this, the first pump light B1 can be split into the first beam S1 and the second beam S2 with different amplitudes by the amplitude splitter, and after the optical switch 111 controls the on/off of the optical path of the first beam S1 and/or the optical path of the second beam S2, the first beam S1 and the second beam S2 with different amplitudes are combined by the polarization coupler to form the second pump light B2.
In some embodiments of the present invention, controlling the on/off of the optical path of the first light beam and/or the optical path of the second light beam by the optical switch comprises:
and the optical switch controls the optical path of the first light beam and the optical path of the second light beam to be alternately switched on and off.
For example, during the first time period, the optical path of the first light beam S1 is controlled to be on, the optical path of the second light beam S2 is controlled to be off, and only the first light beam S1 is transmitted to the beam combining element 112, during the second time period, the optical path of the first light beam S1 is controlled to be off, and the optical path of the second light beam S2 is controlled to be on, and only the second light beam S2 is transmitted to the beam combining element 112. Of course, the present invention is not limited thereto, and the on/off of the first light beam S1 and/or the second light beam S2 can be controlled according to actual needs.
In some embodiments of the present invention, detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light includes:
detecting signal light formed when the detection light and the pump light have different delay times, and obtaining a detection signal of which the light intensity changes along with the delay time;
and demodulating the detection signal, and acquiring the detection information of the object to be detected according to the demodulated detection signal.
Wherein, obtaining the detection information of the object to be detected according to the demodulated detection signal comprises:
and obtaining the change time period of the detection signal according to the detection signal of which the light intensity of the signal light changes along with the delay time, and obtaining the information to be detected of the object to be detected according to the time period.
Wherein obtaining a change time period of the detection signal based on the detection signal in which the light intensity of the signal light changes with the delay time includes: the time period is obtained from a delay time difference between adjacent light intensity peaks or adjacent light intensity troughs of the detection signal.
In an embodiment of the present invention, the detection information includes one or a combination of a thickness of the film layer, a sound velocity in the object to be measured, or an elastic modulus of the object to be measured. In some embodiments of the present invention, the detection information includes a thickness of the object to be measured, and the thickness of the object to be measured is obtained according to the time period and the sound velocity. Or in other embodiments of the present invention, the detection information includes a sound velocity of the object to be measured, and the sound velocity in the object to be measured is obtained according to the time period and the thickness of the object to be measured a.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (16)

1. A measurement system, comprising:
the optical transmitting module is used for generating first pumping light and probe light;
the modulation module is used for modulating the first pump light to form second pump light which irradiates the surface of an object to be detected, acoustic waves are formed in the object to be detected, and the probe light is reflected to form signal light after reaching the surface of the object to be detected;
the modulation module includes: a first beam splitting assembly for splitting the first pump light into a first beam and a second beam, the first and second beams having different optical properties; the optical switch is used for controlling the on-off of the optical path of the first light beam and/or the optical path of the second light beam; the beam combining assembly is used for combining the first beam and the second beam of the split light to form second pump light;
and the detection module is used for detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light.
2. The system of claim 1, wherein the first light splitting component comprises a polarizing beam splitter or an amplitude beam splitter; the polarization beam splitter is used for enabling the first light beam and the second light beam to have different polarization states; the amplitude beam splitter is configured to cause the first beam and the second beam to have different amplitudes.
3. The system of claim 1, wherein the optical switch alternately switches the optical path of the first light beam and the optical path of the second light beam.
4. The system of claim 1, wherein the optical switch comprises one or a combination of a first optical switch and a second optical switch;
the first optical switch is used for controlling the on-off of the optical path of the first light beam;
the second optical switch is used for controlling the on-off of the optical path of the second light beam.
5. The system of claim 1, wherein the modulation module further comprises a radio frequency control unit, the radio frequency control unit being connected to the optical switch;
the radio frequency control unit is used for outputting a control signal to the optical switch, so that the on or off state of the optical switch is controlled through the control signal, and the on or off state of the first light beam and/or the on or off state of the second light beam is controlled through controlling the on or off state of the optical switch.
6. The system of claim 5, wherein the modulation module further comprises a signal generation unit, the signal generation unit being connected to the radio frequency control unit;
the signal generating unit is used for inputting a parameter control signal to the radio frequency control unit so as to control the radio frequency control unit to output the control signal.
7. The system according to claim 6, wherein the optical switch comprises a first optical switch and a second optical switch, the rf control unit comprises a first sub-control unit and a second sub-control unit, the first sub-control unit is configured to generate a first control signal according to the parameter control signal and output the first control signal to the first optical switch, and the second sub-control unit is configured to generate a second control signal according to the parameter control signal and output the second control signal to the second optical switch, so as to control an on or off state of the first optical switch by the first control signal and control an on or off state of the second optical switch by the second control signal; the parameter control signal comprises square waves, and the duty ratio of the parameter control signal is 40% -60%.
8. The system of claim 6, wherein the detection module comprises a detector, a demodulator, and a data processing module;
the detector is used for detecting signal light formed when the detection light and the pump light have different delay times and obtaining a detection signal of the change of the light intensity of the signal light along with the delay time;
the demodulator is used for receiving a reference signal output by the signal generating unit and a detection signal of the light intensity of the signal light output by the detector along with the change of delay time, demodulating the detection signal according to the reference signal and transmitting the demodulated detection signal to the data processing module;
and the data processing module is used for obtaining the detection information of the object to be detected according to the demodulated detection signal.
9. The system of claim 1, wherein the light emitting module comprises:
a laser for generating laser light;
a second light splitting component for splitting the laser light into the first pump light and the probe light;
a time delayer for adjusting a delay time between the probe light and the first pump light or adjusting a delay time between the probe light and the second pump light.
10. The system of claim 1, wherein the optical switch comprises an acousto-optic modulator.
11. The system of claim 1, wherein the first pump light comprises pulsed light and the probe light is pulsed light or continuous light.
12. The system of claim 1, wherein the detection information includes one or a combination of a film thickness, a speed of sound in the test object, or a modulus of elasticity of the test object.
13. A measurement method applied to the measurement system according to any one of claims 1 to 12, the measurement method comprising:
generating first pump light and probe light;
splitting the first pump light into a first beam and a second beam, the first and second beams having different optical properties;
controlling the on-off of the light path of the first light beam and/or the light path of the second light beam through an optical switch, combining the first light beam and the second light beam which are split by light to form second pump light which is irradiated to the surface of an object to be detected to form sound waves in the object to be detected, and reflecting the probe light to form signal light after reaching the surface of the object to be detected;
and detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light.
14. The method of claim 13, wherein splitting the first pump light into a first beam and a second beam comprises:
splitting the first pump light into a first beam and a second beam having different polarization states;
alternatively, the first pump light is split into a first beam and a second beam having different amplitudes.
15. The method of claim 13, wherein controlling the on/off of the optical path of the first light beam and/or the optical path of the second light beam by an optical switch comprises:
and controlling the light path of the first light beam and the light path of the second light beam to be alternately switched on and off through an optical switch.
16. The method of claim 13, wherein detecting the signal light and obtaining the information to be detected of the object to be detected according to the signal light comprises:
detecting signal light formed when the detection light and the pump light have different delay times, and obtaining a detection signal of the light intensity of the signal light changing along with the delay time; and demodulating the detection signal, and acquiring the detection information of the object to be detected according to the demodulated detection signal.
CN202011354760.4A 2020-11-27 2020-11-27 Measuring system and measuring method Pending CN114562943A (en)

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