WO2024060929A1 - Photoacoustic measuring device and film thickness measuring method - Google Patents

Abstract

A photoacoustic measuring device, comprising: a light emitter (000), a controller, an image acquisition part (500), and a detection part (400, 420, 610, 620). The light emitter (000) is used for generating excitation light and detection light. The detection part (400, 420, 610, 620) comprises a one-dimensional position sensor (610) or a two-dimensional position sensor (620), and is used for receiving a detection beam reflected by a measured object (800), to obtain at least an offset of the reflected detection beam. The image acquisition part (500) is used for acquiring an image of light spots of the excitation light and the detection light on the surface of the measured object (800). The controller is used for: receiving the image to determine the relative orientation of an excitation light spot and a detection light spot on the surface of the measured object (800), and according to the relative orientation, controlling the detection part (400, 420, 610, 620) to select the one-dimensional position sensor (610) or the two-dimensional position sensor (620); and acquiring parameters to be measured of the measured object (800). A photoacoustic signal having a higher signal-to-noise ratio is obtained by the position detector (400, 420, 610, 620), so that higher repeated measurement precision for film thickness is obtained. Also disclosed is a film thickness measuring method.

Description

Photoacoustic measurement device and film thickness measurement method

cross reference

This application claims priority to the Chinese application with application number 2022111571237 submitted on September 22, 2022. The contents of the above application are incorporated herein by reference.

Technical field

The invention relates to the field of detection, and in particular to a photoacoustic measuring device and a film thickness measuring method.

Background technique

The photoacoustic measurement mechanism in the prior art is mainly based on the following: short pulse laser is irradiated on the surface of the film sample, and the film sample absorbs photons to generate thermoelastic deformation, forming a deformation zone on the surface; thermoelastic deformation generates sound waves that propagate on the solid surface and inside; longitudinal sound waves The first echo signal is generated when it propagates to the interface (specifically, such as the substrate or the junction between the membrane and the membrane); the first echo signal reaches the upper surface, causing further changes in the deformation; the echo signal rebounds after hitting the upper surface. After the rebound hits the interface, a second echo signal is generated; the second echo signal reaches the upper surface, causing the bulge shape to change again. Of course, the echo signal may also include more than three times. The time interval between echoes reaching the upper surface can be obtained through the detection system, from which the thickness of the film sample can be calculated.

The existing detection system can only detect changes in material reflectivity. When the reflectivity of the material itself changes slightly (such as inert metal material Cu), or when the material structure or surface roughness changes (such as the surface roughness of metal materials after chemical mechanical polishing) When the thickness is larger (or Cu line array, etc.), the material reflectivity change magnitude is low, and it is impossible to obtain a high signal-to-noise ratio photoacoustic signal that can be used to extract film thickness information.

Therefore, it is necessary to provide a new type of photoacoustic measurement equipment and film thickness measurement method to solve the above problems existing in the existing technology.

Contents of the invention

The purpose of this invention is to provide a method that directly measures the beam displacement at the pupil caused by beam deflection by adding a position sensitive detector/device (PSD) to the detection optical path, and then obtains the time when the echo reaches the upper surface, and calculates Film thickness value.

In order to achieve the above objects, in a first aspect, the present invention provides a photoacoustic measurement device, including a light emitter, a controller, an image acquisition component and a detection component; the light emitter is used to generate excitation light and detection light;

The excitation light is projected to the measurement area of the object to be measured along the optical path of the excitation light, and the detection light is projected to the measurement area along the optical path of the detection light. The excitation light forms an acoustic wave in the object to be measured, and the sound wave It is transmitted back to the surface of the measured object through the interface in the measured object and produces deformation in the measurement area; the detection component is used to receive the detection beam reflected by the measured object and generate an output signal, The detection component includes a one-dimensional position sensor or a two-dimensional position sensor to at least obtain the offset of the reflected detection beam, wherein the one-dimensional position sensor and the two-dimensional position sensor are switchable or replaceable during the measurement process. ;

The image acquisition component is used to acquire images of the excitation light and detection light spots on the surface of the object to be measured; the controller is used to receive the image to determine the excitation light spot and the detection light spot. the relative orientation of the position on the surface of the measured object, and control the detection component to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative orientation; the controller is also used to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative orientation. The output signal of the detection component is used to obtain the parameters to be measured of the object to be measured.

By adding a designed position sensor, materials with a smaller material reflectivity response can obtain photoacoustic signals with a higher signal-to-noise ratio through the position sensor, thereby obtaining higher film thickness repeat measurement accuracy and enhancing system robustness. Moreover, according to the relative orientation of the excitation light spot and the detection light spot during measurement, the corresponding position sensor is selected, which further improves the accuracy of the obtained offset and improves the signal-to-noise ratio.

In a further embodiment, controlling the detection component to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative orientation includes: if the relative orientation is along the x direction or the y direction, the detection component The component selects a one-dimensional position sensor, and the detection surface of the one-dimensional position sensor is long The direction of the edge corresponds to said relative orientation;

If the relative orientation is not along the x-direction or the y-direction, the detection component selects a two-dimensional position sensor, and the directions of the two sides of the detection surface of the two-dimensional position sensor correspond to the x-direction and the y-direction respectively, or the detection component selects two one-dimensional position sensors, and the directions of the long sides of the detection surfaces of the two one-dimensional position sensors are mutually orthogonal; wherein the x-direction and the y-direction are two mutually orthogonal directions on the surface of the object to be measured. In a further embodiment, the one-dimensional position sensor includes two output terminals, and the two-dimensional position sensor includes four output terminals;

The detection surface of the one-dimensional position sensor is a rectangular photosensitive surface or consists of two square photosensitive surfaces of the same size; the detection surface of the two-dimensional position sensor is a square photosensitive surface or consists of four identical photosensitive surfaces distributed in a 2×2 array. It consists of a square photosensitive surface.

A further embodiment discloses a photoacoustic measurement device that obtains the offset from the output signal of the one-dimensional position sensor, including:

Wherein, δ is the offset, _I1 and _I2 are the output signals of the two output ends of the one-dimensional position sensor respectively, and L is the effective distance between the two output ends or the diameter of the reflected detection light beam.

According to a further disclosed embodiment of the photoacoustic measurement device, the offset is obtained from the output signal of the two-dimensional position sensor, including:

Among them, δ _x and δ _y are the components of the offset in the x direction and the y direction respectively, I ₁ , I ₂ , I ₃ and I ₄ are respectively the output signals of the four output terminals of the two-dimensional position sensor, I ₁ and I ₂ , I ₃ and I ₄ are respectively the output signals of two adjacent output terminals corresponding to the y direction. I ₁ and I ₄ , I ₂ and I ₃ are respectively the output signals of two adjacent output terminals corresponding to the x direction. The output signal of the output terminal, L _x is the effective distance between _the two output terminals corresponding to the output signals I ₁ and I ₄ respectively or the diameter of the reflected detection beam, L _y is _the corresponding The effective distance between the two output terminals or the diameter of the reflected detection beam.

In some embodiments, a photoacoustic measurement device is disclosed, and the detection component further includes a photodetector to obtain changes in light intensity caused by changes in reflectivity of the object to be measured;

The reflected detection beam passes through the spectroscopic component and is received by the photodetector and the one-dimensional position sensor or the two-dimensional position sensor respectively.

In some other embodiments, a photoacoustic measurement device is further disclosed, wherein the reflected detection light beam is received by the photodetector after passing through an imaging unit, and the magnification of the imaging unit is 1:1; the detection light received by the one-dimensional position sensor or the two-dimensional position sensor is a parallel light beam.

In a possible embodiment, the disclosed photoacoustic measurement device determines the light splitting ratio of the light splitting component based on the one-dimensional position sensor or the two-dimensional position sensor and the saturation power of the photodetector, and the The power of the detection light received by the one-dimensional position sensor, the two-dimensional position sensor, and the photodetector reaches saturation power. By using photoelectric detectors, you can switch between two measurement modes, material reflectivity measurement and drum deflection measurement. To cope with different measurement conditions, you can choose the measurement method with greater responsiveness for testing, and obtain higher results. The signal-to-noise ratio and system repeatability measurement accuracy.

In a second aspect, the present invention also provides a film thickness measurement method, which is applied to the photoacoustic measurement equipment of the first aspect, including: acquiring the excitation light and the detection light at different time delays, The output signal of the detection component;

The controller controls an optical retarder to adjust the optical path difference between the excitation light and the detection light to achieve adjustment of different time delays. The optical retarder is arranged in the optical path of the excitation light and/or the detection light. light path;

Based on the output signal, a detection signal is obtained, the detection signal includes the detection beam offset, or includes the detection beam offset and the change in light intensity caused by the change in reflectivity of the measured object;

The time interval in the time domain of the detection signal is obtained, and the film thickness of the object to be measured is obtained based on the time interval. The time interval corresponds to the time interval between the sound waves reaching the surface of the object to be measured twice before and after.

To further disclose a measurement method in the embodiment, obtaining the film thickness of the object under test based on the time interval includes: obtaining a first time interval based on the offset of the detection beam, and calculating first film thickness;

Based on the change in light intensity caused by the change in reflectivity of the measured object, a second time interval is obtained, and the second film thickness is calculated;

The obtained first film thickness or the second film thickness is used as the film thickness of the measured object; or,

The obtained average value of the first film thickness and the second film thickness is regarded as the film thickness of the measured object.

Regarding the beneficial effects of the above second aspect, please refer to the description in the above first aspect.

Description of the drawings

Figure 1 is a schematic diagram of the architecture of a detection component according to an embodiment of the present invention;

Figure 2 is a schematic diagram of the detection component structure of an embodiment of the present invention;

Figure 3 is a schematic diagram of the detection component structure of an embodiment of the present invention;

Figure 4 is a schematic diagram of an embodiment of a photoacoustic measurement device of the present invention;

Figure 5 is a schematic diagram of the basic structure of the photoacoustic detection principle of the present invention;

Figure 6 is a schematic diagram of an embodiment of a photoacoustic measurement device of the present invention;

Figure 7 is a schematic diagram of an embodiment of a photoacoustic measurement device of the present invention;

Figure 8 is a schematic diagram of multiple embodiments of the position sensor of the present invention;

Figure 9 is a schematic flow chart of the film thickness measurement method of the present invention.

Figure markings: 000-laser; 120-beam splitter; 130-chopper; 140-beam combiner; 210-first reflector; 220-optical delay; 230-second reflector; 250-first condenser; 270-second condenser; 260-collimator; 300-square beam splitter; 310-first light-splitting component; 320 second light-splitting component; 400-position sensor; 420-photodetector; 410-first phase-locked amplifier; 411-second phase-locked amplifier; 800-object to be measured; 810-bulge on sample surface; 510-excitation beam; 520-detection beam; 500-image acquisition component; 610-one-dimensional position sensor; 620-two-dimensional position sensor.

Detailed ways

The technical solutions in the embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention. Among them, in the description of the embodiments of the present invention, the terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the specification and appended claims of this application, the singular expressions "a," "the," "above," "the" and "the" are intended to also include, for example, "a "or more" unless the context clearly indicates otherwise. It should also be understood that in the following embodiments of this application, "at least one" and "one or more" refer to one or more than two (including two). The term "and/or" is used to describe the relationship between associated objects, indicating that there can be three relationships; for example, A and/or B can mean: A exists alone, A and B exist simultaneously, and B exists alone, Where A and B can be singular or plural. The character "/" generally indicates that the related objects are in an "or" relationship.

Reference in this specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Therefore, the phrases "in one embodiment", "in some embodiments", "in other embodiments", "in other embodiments", etc. appearing in different places in this specification are not necessarily References are made to the same embodiment, but rather to "one or more but not all embodiments" unless specifically stated otherwise. The terms “including,” “includes,” “having,” and variations thereof all mean “including but not limited to,” unless otherwise specifically emphasized. The term "connected" includes both direct and indirect connections unless otherwise stated. “First” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features.

In the embodiments of the present invention, words such as “exemplarily” or “for example” are used to represent examples, illustrations or explanations. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the invention is not to be construed as preferred or advantageous over other embodiments or designs. Rather, the use of the words "exemplarily" or "for example" is intended to present the relevant concepts in a concrete manner.

The embodiment of the present invention provides a photoacoustic measurement device. As shown in Figure 4, the beam emitted by the laser 000 is divided into an excitation beam 510 and a detection beam 520 by the beam splitter 120. The excitation light optical path is provided with a chopper 130. The detection light optical path is provided with a first reflecting mirror 210, an optical retarder 220 and a second reflecting mirror 230. The excitation beam 510 and the detection beam 520 are focused on the surface of the object 800 by the second condenser 270 after passing through the beam combiner 140, and the detection light reflected by the sample surface is received by the detection component. The detection component includes a position sensor 400 and a lock-in amplifier 410. The structural arrangement of the detection component can adopt any technical solution in the creative embodiments of the present invention. As an example, the detection component as shown in Figures 1-3 can be used. Structural settings; among them, different structural settings of the detection component are replaceable or switchable. By adding a Position Sensing Detector (PSD) at the pupil of the detection light path, such as 400 in Figure 4, the beam displacement at the pupil caused by the deflection of the detection beam 520 is directly measured, and then the time for the echo to reach the upper surface is obtained and calculated Film thickness value. The bulge-deflected light beam generated by the surface of the object 800 is collimated into parallel light by the collimator 260. A position sensor 400 is placed on the back focal plane of the collimator 260 in Figure 4.

For example, as shown in Figure 5, the excitation light and detection light beams are focused on the surface of the object to be measured through a condenser mirror. After the photoacoustic effect is stimulated by the excitation light, the sound waves generated by the photoacoustic effect propagate between the film layers. When reaching the interface between the top material and the air, the stress and strain will cause local bulges on the surface of the material on the order of picometers - bulges 810 on the sample surface. At this time, the incident detection light converges to the position where the bulges cause a large surface tilt, that is, a bulge 810 is generated. The maximum position of the first derivative/gradient of the bulge morphology. Generally, there is a micron-level position offset between the focus center position of the detection light and the excitation light. The specific offset is related to the spot shape, energy distribution and spot size of the excitation light. Collimation The optical element is located between the measurement area and the position sensor 400 . The reflected detection light beam is collimated by the collimating mirror 260 and then received by the position sensor 400 .

The sound wave generated by the photoacoustic effect propagates longitudinally, will be reflected at the interface and then return to the sample surface. When the sound wave does not reach the surface, the detection light beam is reflected by the sample surface, which is generally approximate to mirror reflection. The detection light beam follows the route shown by the dotted line. Propagation (see Figure 5); when the sound wave generated by the photoacoustic effect reaches the sample surface, the sample surface again generates local surface bulges, that is, the size of the bulge 810 on the sample surface changes, thereby causing the position of the detection beam to deviate relative to the excitation beam. When the displacement changes, the offset of the detection beam is directly obtained through the position sensor 400. Based on the changing trend of the offset of the detection beam, the time for the echo to reach the upper surface of the sample is obtained to calculate the film thickness.

The surface convexity causes the surface where the detection light focus point is tilted. Assume that the tilt angle of the sample surface convexity is θ, and the entire reflected detection light beam is deflected 2θ, as shown by the solid line in Figure 5. The resulting offset δ can be expressed by the following formula;
δ=f×tan2θ——Formula 1;

Where, f is the focal length of the collimating lens 260. By placing the position sensor 400 on the back focal plane of the collimating lens 260, the offset can be measured. Knowing the focal length f of the collimating lens, the bulge tilt angle θ can be further obtained.

In some disclosed embodiments, the photoacoustic measurement device, as shown in Figure 6, the detection component includes a photodetector 420 and a position sensor 400, the photoacoustic measurement device also includes a spectroscopic component 300, and the After the detection beam passes through the light splitting component, it is divided into two parts. One part is received by the photodetector 420 and the other part is received by the position sensor 400 .

In some embodiments, the detection light beam is bulged and deflected after passing through the surface of the sample to be measured. As shown in Figure 6, it is collimated into parallel light through the collimating mirror 260. A planar beam splitter is placed behind the collimating mirror 260. The specific placement position of the device 300 and the planar light splitting device 300 can be near the back focal plane of the collimating mirror 260. The specific splitting ratio can be designed and adjusted according to the saturation power of the detector corresponding to the two-channel light. The default splitting here is 50:50, allowing photoelectric detection. The power of the optical signals received by the detector 420 and the position sensor 400 are both close to their respective saturation powers.

The spectroscopic device 300 splits the detection beam into two: one beam is focused on the photodetector 420 through the focusing lens 250 and is used to measure changes in material reflectivity; the other beam is directly incident on the photosensitive surface of the position sensor 400 for measuring Measure the detection beam deflection caused by the bulge. Both measurement modes can obtain the time when the echo reaches the upper surface, which can be used to calculate the film thickness value on the surface of the object to be measured. After the detection beam is split into two by the spectroscopic device 300, one of the beams is focused on the photodetector 420 through the focusing lens for measuring the change in material reflectivity, and the other beam is directly incident on the photosensitive surface of the position sensor 400 for measuring Measure the deflection/displacement of the detection beam caused by the bulge. Both measurement modes can obtain the time when the echo reaches the upper surface and calculate the film thickness value. It depends on the material of the sample to be tested, surface roughness and geometric structure, etc. Different quantities can be selected. test method. The application of two measurement modes makes the measurement equipment more universal and can be used to measure film thickness of different materials. It has a high signal-to-noise ratio in a variety of measurement scenarios and obtains film thickness with higher accuracy. .

In other embodiments, the photoacoustic measurement equipment includes the spectroscopic optical element, specifically The square beam splitter 300 in Figure 6 is used to divide the detection beam into two parts. One part passes through the square beam splitter 300 and is received by the photodetector 420, and the other part is reflected by the square beam splitter 300 and is The position sensor 400 receives a lock-in amplifier for respectively receiving the output signal of the photodetector and the output signal of the position sensor. Switch between the two measurement modes at will to cope with different measurement conditions and choose the measurement method with greater responsiveness for testing to obtain higher signal-to-noise ratio and system repeatability measurement accuracy.

In other embodiments, the photoacoustic measurement equipment, as shown in Figure 7, can achieve two types of measurements through the square beam splitter 300 and subsequent detection devices (photodetector 420 and position sensor 400). model. The two sets of output signals generated can be connected to the signal input terminals of the dual-channel lock-in amplifier respectively, or connected to two lock-in amplifiers respectively. The host computer 900 can directly control the dual-channel lock-in amplifier through the communication interface, or establish connections with the two lock-in amplifiers respectively. By connecting a lock-in amplifier 410 or 411, the system can be switched between the material reflectance measurement mode and the deflection measurement mode through the control program.

The collimator 260 and the condenser 270 form a Kepler beam expansion system to image the object 800. Generally, the scale of the focused light spot is between several and tens of microns. For the reflectivity measurement mode, if a 1:1 magnification system is used, the size of the light spot on the photosensitive surface/image plane of the photodetector is consistent with the size of the light spot on the surface of the sample to be measured. At this time, the size of the photosensitive surface of the photodetector is generally in the order of mm. Even if the light beam is partially deflected due to system vibration, environmental disturbance, sample bulging and other factors, according to the imaging principle, the position and size of the light spot on the imaging plane will not change. Therefore, the signal size is not affected by these disturbance factors and has good robustness. For most materials, such as W, Mo and other materials, the photoacoustic signal can be measured by the reflectivity measurement mode; some materials, such as Cu, have a metal film surface with a large roughness after chemical mechanical grinding, or special structures such as Cu line arrays, and the amplitude of the material reflectivity signal change is low, so the deflection measurement mode can be used for photoacoustic signal measurement.

For the deflection measurement mode, it can have strong signal amplitude for most materials, so it can be adapted to most working conditions. However, any noise source that affects the direction of the beam will have a noisy impact on the deflection data, such as the impact on the pointing stability of the light source, the impact of mechanical vibration on individual reflectors, etc. According to the actual conditions of the system, such as the performance of the femtosecond laser and the type of material to be measured, the two measurement modes can be switched.

In some embodiments, the photoacoustic measurement equipment, as shown in Figure 7, also includes a first condenser optical element, specifically the first condenser lens 250 in Figure 7. The first condenser mirror 250 is located between the square beam splitter 300 and the photodetector 420 , and the collimating mirror 260 is located between the measurement area of the measured object 800 and the square beam splitter 300 .

In some embodiments, the photoacoustic measurement equipment, as shown in Figure 7, also includes a light source component, specifically the laser 000 in Figure 7, and a spectroscopic optical component, specifically as shown in Figure 7 Middle beam splitter 120, the light source component is used to provide a source beam. The source beam is divided into two parts after passing through the spectroscopic optical component, one part is the excitation beam 510, and the other part is the detection beam 520. The photoacoustic measurement equipment also includes a light combining optical component, specifically a beam combiner 140 in Figure 7. The light combining optical component is used to combine the excitation beam and the detection beam into one, and combine the two. A light beam of one is projected to the measurement area of the object to be measured, specifically the object to be measured 800 in Figure 7 .

In some embodiments, the photoacoustic measurement device, as shown in Figure 7, also includes a chopper optical component, specifically the chopper 130 in Figure 7. In the optical chopper component It is located in the optical path of the excitation light, specifically between the beam splitter 120 and the beam combiner 140 in Figure 7. After the excitation beam passes through the chopper optical component, it is received by the beam combiner 140. The optical chopper component is used to To modulate the excitation light, the chopper 130 can be an acousto-optic modulator or an electro-optic modulator; it also includes an optical retarder 220 disposed in the optical path of the detection light, and the optical retarder 220 is located between the beam splitter 120 and the beam combiner 140 During this time, the detection beam passes through the optical retarder 220 and is received by the beam combiner 140. The optical retarder 220 is used to phase delay the detection beam; a first reflector 210 and a second reflector are also provided in the detection optical path. Mirror 230 , the first reflecting mirror 210 is located between the beam splitter 120 and the optical retarder 220 , and the second reflecting mirror 230 is located between the optical retarder 220 and the beam combiner 140 .

The photoacoustic measurement equipment provided in the above embodiments also includes a controller and an image acquisition component (not shown in Figures 4 and 6-7), wherein the detection component is used to receive the detection beam reflected by the object to be measured and generate an output signal, The position sensor includes a one-dimensional position sensor or a two-dimensional position sensor to at least obtain the offset of the reflected detection beam, wherein the one-dimensional position sensor and the two-dimensional position sensor are switchable or replaceable during the measurement process. ; Image acquisition component 500, as shown in Figure 1, Figure 2, and Figure 3, is used to obtain Obtain the image of the excitation light and the detection light spot on the surface of the object to be measured; the controller is used to receive the image to determine the excitation light spot and the detection light spot on the surface of the object to be measured. The relative orientation of the position can be understood as the relative orientation is the direction from the center of mass of one light spot to the center of mass of another light spot on the surface of the object to be measured. The controller can obtain two images based on the image of the excitation light spot and the image of the detection light spot. The centroid of the light spot can then determine the relative orientation.

The detection component includes a one-dimensional position sensor 610, as shown in Figure 1 or 2; the detection component can also include a photodetector 420 and a one-dimensional position sensor 610, as shown in Figure 2; the detection component can also be configured to include a Two-dimensional position sensor 620, as shown in Figure 3 .

According to the relative orientation, the controller controls the detection component to select the one-dimensional position sensor 610 or the two-dimensional position sensor 620, that is, according to the relative orientation, the detection component is set to two one-dimensional positions as shown in Figure 1 or 2 The sensor 610 may be configured as a two-dimensional position sensor 620 as shown in Figure 3; as shown in Figure 1, two one-dimensional position sensors 610 are provided, wherein the direction of the long side of the detection surface of the two one-dimensional position sensors orthogonal to each other; the controller is also used to obtain the parameters to be measured of the object to be measured according to the output signal of the detection component. The technical effect of selecting the corresponding position sensor according to the relative orientation: it can select the appropriate position sensor according to the direction of the offset, improve the accuracy of obtaining the offset, and improve the signal-to-noise ratio. At the same time, consider the bandwidth and accuracy of sensors at different positions to adapt to different measurement needs to ensure that the measurement accuracy and measurement efficiency are improved under different working conditions. In actual measurement, the solution provided by the above embodiment can enable the position sensor to accurately match the deflection direction of the detection beam, thereby further improving the accuracy of the obtained offset of the detection beam, thereby improving the film thickness measurement accuracy.

In a further embodiment, controlling the detection component to select the one-dimensional position sensor 610 according to the relative orientation includes: if the relative orientation is along the x direction or the y direction, the detection component selects the one-dimensional position sensor. 610, and the direction of the long side of the detection surface of the one-dimensional position sensor 610 corresponds to the relative orientation; if the relative orientation is not along the x direction or the y direction, the detection component selects a two-dimensional position sensor, and the The directions of the two sides of the detection surface of the two-dimensional position sensor correspond to the x direction and the y direction respectively, or the detection component selects two one-dimensional position sensors, and the detection surfaces of the two one-dimensional position sensors The directions of the long sides are orthogonal to each other.

It can be understood that the coordinate system of the detection surface of the position sensor corresponds to the coordinate system of the surface of the measured object. As shown in Figure 4, a local coordinate system O-XYZ is established on the surface of the measured object 800, where the x direction and the y direction are two mutually orthogonal directions on the surface of the object to be measured, z is the direction perpendicular to the surface of the object to be measured; the detection surface of the position sensor 400 establishes a coordinate system O'-X'Y'Z', where the x' direction Corresponds to the x direction, and the y' direction corresponds to the y direction. The images of the excitation light spot and the detection light spot on the surface 800 of the object to be measured are obtained by the image acquisition component 500, and the relative orientations of the local coordinate system O-XYZ where the two spots are located are obtained. The direction from the centroid of the detection light spot to the centroid of the excitation light spot is For example, it can be X+/X-/Y+/Y-. The detection beam behind the collimator 260 is in the local coordinate system O'-X'Y'Z' of the position sensor 400, and the deflection direction corresponds to '-/Y'+/Y'-, select matching position sensor device design according to different relative orientations, and obtain beam deflection information and film thickness information. The above solution improves the accuracy of the acquired detection beam offset.

The relative orientation is along x (X+/X-) or y (Y+/Y-). The detection component includes at least one one-dimensional position sensor, wherein the direction of the long side of the detection surface of the at least one one-dimensional position sensor corresponds to the relative orientation, that is, The detection component shown in Figure 1 may include two one-dimensional position sensors, or may include one position sensor (not shown in the figure). The relative orientation is not along x or y. The detection light is received by two one-dimensional position sensors after splitting. The two one-dimensional position sensors respectively obtain the components of the offset in the two orthogonal directions, and the actual offset can be obtained.

In some embodiments, the relative orientation is not along x or y, and the offset of the reflected detection light can be obtained by a two-dimensional position sensor. As shown in Figure 3, the reflected detection light 520 is set on the propagation path. A spectroscopic component 310. After passing through the first spectroscopic component 310, a part of the detection light is reflected by the first spectroscopic component 310 to the image acquisition component 500 to obtain the detection light spot image. The detection light transmitted through the first spectrometry component 310 continues to propagate and is captured by a second spectrophotometer. The dimensional position sensor 620 receives. In addition, the image acquisition component 500 also receives the excitation light beam to obtain an image of the excitation light spot.

In a possible embodiment, the structure of the detection component as shown in Figure 1 or the structure of the detection component as shown in Figure 3 can be improved, and a photoelectric detector is provided in the detection system to receive the partially reflected detection beam, so that the detection component can also It can detect changes in surface reflectivity of the object being measured. As an example, for Figure 1 The structure of the detection component shown is improved. As shown in Figure 2, the reflected detection light 520 passes through the first spectroscopic component 310 during propagation, and a part of the light beam is reflected by the first spectroscopic component 310 to the image acquisition component 500 to obtain the detection light. Spot image, the detection light transmitted through the first spectroscopic component 310 propagates to the second spectroscopic component 320, the detection light reflected by the second spectroscopic component 320 is received by the photodetector 420, and the detection light transmitted by the second spectroscopic component 320 passes through the square The beam splitter 300 is then divided into two parts, which are respectively received by two one-dimensional position sensors 610. In addition, the image acquisition component 500 also receives the excitation light beam to obtain an image of the excitation light spot. Similarly, the photodetector disclosed in FIG. 2 above can also be applied to the detection component shown in FIG. 3 . Obviously, the detection component structures disclosed in the above embodiments can be applied to photoacoustic measurement equipment.

According to the relative orientation of the actual focus position of the detection beam and the focus center position of the excitation light in the local coordinate system O-XYZ where the sample is located, the beam center of mass of the detection beam will deflect to different directions in the local coordinate system O'-X'Y'Z' of the position sensor. , can be X'+/X'-/Y'+/Y'-. When the detection light spot is at the positive X position X+ of the excitation light spot, the deflection direction of the detection beam in the local coordinate system of the position sensor is the X' positive position To the position X-, the deflection direction of the detection beam in the local coordinate system of the position sensor is the X' negative position X'-; a similar situation also applies to the Y direction.

In a possible embodiment of the photoacoustic measurement device, if the relative orientation is not along the x direction or the y direction, the detection component selects a two-dimensional position sensor, and the two sides of the detection surface of the two-dimensional position sensor The directions correspond to the x direction and the y direction respectively, or the detection component selects two one-dimensional position sensors, and the directions of the long sides of the detection surfaces of the two one-dimensional position sensors are orthogonal to each other.

In some other embodiments, the photosensitive surface of the position sensor in the photoacoustic measurement device has several deformation designs, wherein the position sensor is shown in FIG8 , one embodiment is composed of photoelectric detector elements with square/rectangular photosensitive surfaces, or, in another embodiment, the position sensor is composed of two photoelectric detector elements with square photosensitive surfaces of equal size arranged side by side in an axisymmetric manner, or, in another embodiment, the position sensor is composed of four photoelectric detector elements with square photosensitive surfaces of equal size arranged in a center-symmetrical manner. Different position sensor design schemes can be applied to different measurement scenarios while taking into account the detection accuracy and response speed of the position sensor, and, in the measurement process, according to the detection The actual direction/relative orientation of the beam deflection, the equipment automatically selects/matches the appropriate layout of the detection components, further improving the detection accuracy of the beam deflection, thereby improving the signal-to-noise ratio of the photoacoustic measurement and improving the measurement accuracy of the film thickness.

In some embodiments of the present application, the embodiment of the present invention also discloses a photoacoustic measurement device, the one-dimensional position sensor 610 includes two output terminals, and the two-dimensional position sensor 620 includes four output terminals; the one-dimensional position sensor 610 includes two output terminals; The detection surface of the two-dimensional position sensor 610 is a rectangular photosensitive surface, as in case B in Figure 8, or is composed of two square photosensitive surfaces of the same size as in case C in Figure 8; the detection surface of the two-dimensional position sensor 620 is A square photosensitive surface as in case A in Figure 8, or consisting of four square photosensitive surfaces of the same size distributed in a 2×2 array as in case D in Figure 8.

In some further embodiments of the present application, the photoacoustic measurement device obtains the offset from the output signal of the one-dimensional position sensor 610, including:

Wherein, δ is the offset, I ₁ and I ₂ are the output signals of the two output terminals of the one-dimensional position sensor respectively, and L is the effective distance between the two output terminals or the diameter of the reflected detection beam. . The two photosensitive surface structures are shown in C in Figure 8. L is the spot diameter on the detection surface (the diameter of the reflected detection beam), and the calculation is more accurate. The spot diameter is the diameter in the direction, which is the length direction of the rectangular photosensitive surface in the one-dimensional position sensor 610, that is, the X direction shown in C in Figure 8, or two squares of the same size in the one-dimensional position sensor 610 The length direction of the rectangular photosensitive surface. The position sensor of a single rectangular photosensitive surface is shown as B in Figure 8. L is the effective distance between the photocurrent output terminals, and the calculation is more accurate.

In some embodiments of the present application, the photoacoustic measurement device obtains the offset from the output signal of the two-dimensional position sensor 620, including:

Among them, δ _x and δ _y are the components of the offset in the x direction and y direction respectively, I ₁ , I ₂ , I ₃ and I ₄ are respectively the output signals of the four output terminals of the two-dimensional position sensor, I ₁ and I ₂ , I ₃ and I ₄ are respectively the output signals of two adjacent output terminals corresponding to the y direction, I ₁ and I ₄ , I ₂ and I ₃ are respectively the output signals of two adjacent output terminals corresponding to the x direction, L _x is the effective distance between the two output terminals corresponding to the output signals I ₁ and I ₄ respectively or the detection of the reflection The diameter of the beam, Ly _y, is the effective distance between the two output terminals corresponding to the output signals I ₁ and I ₂ respectively or the diameter of the reflected detection beam.

In one possible case of the present application, the photoacoustic measurement device, the detection component also includes a photodetector 420 to obtain the light intensity change caused by the reflectivity change of the object to be measured; the reflected detection beam is received by the photodetector 420 and the one-dimensional position sensor 610 or the two-dimensional position sensor 620 respectively after passing through the light splitting component (not shown in the figure). In the photoacoustic measurement device in a further embodiment, the reflected detection beam is received by the photodetector after passing through an imaging unit, and the magnification of the imaging unit (Kepler type) is 1:1, that is, the spot size of the detection beam on the surface of the object to be measured is consistent with its spot size on the detection surface of the photodetector.

The detection light received by the one-dimensional position sensor or the two-dimensional position sensor is a parallel light beam. Specifically, select a matching position sensor design according to the different deflection directions of the detection beam. The offset in the X' direction and the +/- offset can be measured. If you need to choose, the photocurrent differential signal can be used to feed back the detection beam in X'. The position sensor design of the direction offset _δ Thickness value, the calculation principle here is the same as the material reflectivity echo calculation method.

In some embodiments of the present application, the selection of a position sensor design mainly considers two aspects: position detection sensitivity/accuracy; and detector bandwidth. For the same detector material, generally the larger the photosensitive surface, the larger the junction capacitance of the photodetector and the smaller the bandwidth of the photodetector. At the same time, the saturated optical power that the detector can receive will also increase with the increase of the photosensitive area. As the size increases, the signal-to-noise ratio of the photoelectric signal also increases. In addition, as the acceptable light spot area becomes larger, the position detection accuracy of the position sensor will also increase. An appropriate position sensor design can be selected based on the requirements for detection bandwidth and detection position accuracy under actual working conditions.

In other embodiments, the position sensor design is shown in Figure 8A, consisting of a square photosensitive It is composed of a surface photodetector element and is a two-dimensional position sensor. The length of the position sensor in the x direction is Lx, and the length in the y direction is Ly, where Ly=Lx. There is a pin on each of the four corners of a single detection surface to derive photocurrent. Based on the photocurrent, the offset of the detection beam in the X/Y direction can be calculated, and then the angular deflection of the detection beam and the time when the deflection occurs can be calculated. The conversion formula of the offset δx and δy between the photocurrent and the detection beam in the x and y directions can be expressed as Among them, Lx and Ly are the lengths of the photosensitive surface in the x and y directions respectively - corresponding to the effective distance between the photocurrent output ends.

In other embodiments, the position sensor design scheme is B in Figure 8, which is a one-dimensional position sensor, consisting of a photodetector element with a long and narrow rectangular photosensitive surface. The length of the one-dimensional position sensor in the x direction is Lx>Ly. , the X-direction offset can be obtained. Rotate this design 90 degrees to obtain a photodetector element with a rectangular photosensitive surface in the Y direction. The length of the one-dimensional position sensor in the y direction Ly>Lx can be used to obtain the offset in the Y direction.

For the design of a single detection surface, as shown in Figure 8B, two pins in the X direction derive photocurrent. The conversion formula between the photocurrent and the offset δ of the detection beam in the x direction can be expressed as Where L is the length of the photosensitive surface in the x direction - the effective distance between the photocurrent output terminals. In the Y-direction design, the one-dimensional position sensor shown in Figure 8B is rotated 90 degrees, and the conversion formula of the photocurrent and the offset δ of the detection beam in the y-direction can be expressed as Where L is the length of the photosensitive surface in the y direction - the effective distance between the photocurrent output terminals.

In other embodiments, the position sensor is a one-dimensional position sensor. The specific design scheme is shown in Figure 8 as case C. It consists of two photodetector elements with square photosensitive surfaces of equal size, which can detect the offset in the X direction. Rotate this design 90 degrees to obtain a dual photodetector element design in the Y direction, which can detect the offset in the Y direction.

According to the difference between the photocurrent values I ₁ and I ₂ obtained from the detection photosensitive surface 1 and the detection photosensitive surface 2, the deflection amount of the detection beam in the X direction can be calculated, and then the angular deflection size of the detection beam and the time when the deflection occurs can be calculated. between. The conversion formula between the photocurrent and the beam offset δ in the x direction can be expressed as where L is the diameter of the detection light spot in the x direction. In the Y-direction design, the one-dimensional position sensor shown in Figure 8C is rotated 90 degrees, and the conversion formula of the photocurrent and the offset δ of the detection beam in the y-direction can be expressed as where L is the diameter of the detection light spot in the y direction.

In other embodiments, the position sensor is a two-dimensional position sensor. The design scheme is in case D in Figure 8. There are four detection photosensitive surfaces distributed in a 2×2 array, and each of the four corners has a pin to derive the photocurrent. Based on The photocurrent can be used to calculate the offset of the detection beam in the X/Y direction, and then calculate the angular deflection of the detection beam and the time when the deflection occurs. According to the difference between the photocurrent value/photovoltage value obtained by detecting photosensitive surface 1, detecting photosensitive surface 2, detecting photosensitive surface 3, and detecting photosensitive surface 4, the offset amount of the detection beam in the X/Y direction can be calculated, and then Calculate the angle deflection of the detection beam and the time when the deflection occurs. The conversion formula of the offset δx and δy between the photocurrent and the detection beam in the x and y directions can be expressed as Among them, Lx is the diameter of the light spot in the x direction, and Ly is the diameter of the light spot in the y direction.

The position sensor design is shown in Figure 8 B and Figure 8 C. They are both unidirectional position detection designs that can measure the deflection of the bulge in one direction. Two position sensors can also be combined to detect deflection in any direction. The design solution is simplified, the subsequent circuit design requirements are reduced, it is easy to implement and the cost is low. Among them, the design scheme B in Figure 8 is compared to the design scheme C in Figure 8. The photosensitive surface area is larger, the junction capacitance is large, and the photocurrent is large, so the position accuracy is high, but the bandwidth is low.

The position sensor design is shown in Figure 8 A and Figure 8 D, which can realize position detection in both X/Y directions and can measure deflection in both directions of the bulge, that is, it can detect deflection in any direction, reducing the impact of excitation light spots and detection light spots. The relative orientation requirements, that is, both X/Y directions are applicable, which enhances the flexibility of the equipment and has high system integration, but requires higher requirements for subsequent circuit design.

The present invention also provides a film thickness measurement method, as shown in Figure 9. The film thickness measurement method is applied to the photoacoustic measurement equipment disclosed in the aforementioned embodiments, and includes:

Step 100: Obtain the output signal of the detection component under different time delays of the excitation light and the detection light;

Step 200: The controller controls an optical retarder to adjust the optical path difference between the excitation light and the detection light to achieve adjustment of different time delays. The optical retarder is arranged in the optical path of the excitation light and/or The optical path of the detection light;

Step 300: acquiring a detection signal based on the output signal, wherein the detection signal includes the detection beam offset, or includes the detection beam offset and a light intensity change caused by a reflectivity change of the object being measured;

Step 400: Obtain the time interval in the time domain of the detection signal, and obtain the film thickness of the object to be measured based on the time interval. The time interval corresponds to the time when the sound wave reaches the surface of the object to be measured twice before and after. time interval.

In a further embodiment of the film thickness measurement method, obtaining the film thickness of the measured object based on the time interval includes:

Step 1000: Obtain the first time interval based on the offset of the detection beam, and calculate the first film thickness;

Step 2000: Obtain the second time interval based on the change in light intensity caused by the change in reflectivity of the measured object, and calculate the second film thickness;

Step 3000: Use the obtained first film thickness or the second film thickness as the film thickness of the measured object; or, use the average value of the obtained first film thickness and the second film thickness As the film thickness of the measured object.

Although the embodiments of the present invention have been described in detail above, it will be obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are within the scope and spirit of the invention as described in the claims. Furthermore, the invention described herein is capable of other embodiments and of being practiced or carried out in various ways.

Claims (10)

1. A photoacoustic measurement device, characterized in that it comprises: a light emitter, a controller, an image acquisition component and a detection component; the light emitter is used to generate excitation light and detection light;

   The excitation light is projected to the measurement area of the object to be measured along the optical path of the excitation light, and the detection light is projected to the measurement area along the optical path of the detection light. The excitation light forms an acoustic wave in the object to be measured, and the sound wave It is transmitted back to the surface of the measured object through the interface in the measured object and generates deformation in the measurement area;

   The detection component is used to receive the detection beam reflected by the object to be measured and generate an output signal. The detection component includes a one-dimensional position sensor or a two-dimensional position sensor to at least obtain the offset of the reflected detection beam, Wherein, the one-dimensional position sensor and the two-dimensional position sensor are switchable or replaceable during the measurement process;

   The image acquisition component is used to acquire images of the light spots of the excitation light and the detection light on the surface of the object to be measured;

   The controller is configured to receive the image to determine the relative orientation of the excitation light spot and the detection light spot on the surface of the object to be measured, and control the detection component to select the one based on the relative orientation. dimensional position sensor or said two-dimensional position sensor;

   The controller is also used to obtain the parameters to be measured of the object to be measured based on the output signal of the detection component.
2. The photoacoustic measurement device according to claim 1, wherein controlling the detection component to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative orientation includes:

   If the relative orientation is along the x-direction or the y-direction, the detection component selects a one-dimensional position sensor, and the direction of the long side of the detection surface of the one-dimensional position sensor corresponds to the relative orientation;

   If the relative orientation is not along the x direction or the y direction, the detection component selects a two-dimensional position sensor, and the directions of the two sides of the detection surface of the two-dimensional position sensor correspond to the x direction and the y direction respectively, or , the detection component selects two one-dimensional position sensors, and the two one-dimensional position sensors The directions of the long sides of the detection surface of the sensor are orthogonal to each other;

   Wherein, the x direction and the y direction are two mutually orthogonal directions on the surface of the object to be measured.
3. The photoacoustic measurement device according to claim 2, wherein the one-dimensional position sensor includes two output terminals, and the two-dimensional position sensor includes four output terminals;

   The detection surface of the one-dimensional position sensor is a rectangular photosensitive surface or consists of two square photosensitive surfaces of the same size; the detection surface of the two-dimensional position sensor is a square photosensitive surface or consists of four identical photosensitive surfaces distributed in a 2×2 array. It consists of a square photosensitive surface.
4. The photoacoustic measurement device according to claim 3, wherein the offset is obtained from the output signal of the one-dimensional position sensor, including:
   

   Wherein, δ is the offset, I ₁ and I ₂ are the output signals of the two output terminals of the one-dimensional position sensor respectively, and L is the effective distance between the two output terminals or the diameter of the reflected detection beam. .
5. The photoacoustic measurement device according to claim 3, wherein the offset is obtained from the output signal of the two-dimensional position sensor, including:
   

   Among them, δ _x and δ _y are the components of the offset in the x direction and the y direction respectively, I ₁ , I ₂ , I ₃ and I ₄ are respectively the output signals of the four output terminals of the two-dimensional position sensor, I ₁ and I ₂ , I ₃ and I ₄ are respectively the output signals of two adjacent output terminals corresponding to the y direction. I ₁ and I ₄ , I ₂ and I ₃ are respectively the output signals of two adjacent output terminals corresponding to the x direction. The output signal of the output terminal, L _x is the effective distance between _the two output terminals corresponding to the output signals I ₁ and I ₄ respectively or the diameter of the reflected detection beam, L _y is _the corresponding The effective distance between the two output terminals or the diameter of the reflected detection beam.
6. The photoacoustic measurement equipment according to any one of claims 1 to 5, wherein the detection component further includes a photodetector to obtain changes in light intensity caused by changes in reflectivity of the object to be measured;

   The reflected detection beam passes through the spectroscopic component and is received by the photodetector and the one-dimensional position sensor or the two-dimensional position sensor respectively.
7. The photoacoustic measurement equipment according to claim 6, wherein the reflected detection beam is received by the photodetector after passing through an imaging unit, and the magnification of the imaging unit is 1:1;

   The detection light received by the one-dimensional position sensor or the two-dimensional position sensor is a parallel light beam.
8. The photoacoustic measurement device according to claim 6, wherein the light splitting ratio of the light splitting component is determined by the saturation power of the one-dimensional position sensor or the two-dimensional position sensor and the photodetector, and the The power of the detection light received by the one-dimensional position sensor, the two-dimensional position sensor, and the photodetector reaches saturation power.
9. A film thickness measurement method, characterized in that the film thickness measurement method is applied to the photoacoustic measurement equipment according to any one of claims 1 to 8, including:

   Obtain the output signal of the detection component under different time delays of the excitation light and the detection light;

   The controller controls an optical retarder to adjust the optical path difference between the excitation light and the detection light to achieve adjustment of different time delays. The optical retarder is arranged in the optical path of the excitation light and/or the detection light. light path;

   Based on the output signal, a detection signal is obtained, the detection signal includes the detection beam offset, or includes the detection beam offset and the change in light intensity caused by the change in reflectivity of the measured object;

   The time interval in the time domain of the detection signal is obtained, and the film thickness of the object to be measured is obtained based on the time interval. The time interval corresponds to the time interval between the sound waves reaching the surface of the object to be measured twice before and after.
10. The film thickness measurement method of claim 9, wherein obtaining the film thickness of the measured object based on the time interval includes:

    Based on the offset of the detection beam, a first time interval is obtained, and a first film thickness is calculated;

    Based on the change in light intensity caused by the change in reflectivity of the measured object, a second time interval is obtained, and the second film thickness is calculated;

    The obtained first film thickness or the second film thickness is used as the film thickness of the measured object; or,

    The obtained average value of the first film thickness and the second film thickness is regarded as the film thickness of the measured object.