A photoacoustic measuring device and a film thickness measuring method

Abstract

This invention provides a photoacoustic measurement device, comprising: a light emitter, a controller, an image acquisition component, and a detection component; the light emitter generates excitation light and probe light; the detection component includes a one-dimensional position sensor or a two-dimensional position sensor, used to receive the probe light beam reflected by the object under test, to obtain at least the offset of the reflected probe light beam; the image acquisition component acquires images of the light spots of the excitation light and the probe light on the surface of the object under test; the controller receives the images to determine the relative orientation of the excitation light spot and the probe light spot on the surface of the object under test, and controls the detection component to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative orientation; and acquires the test parameters of the object under test. A higher signal-to-noise ratio photoacoustic signal is obtained through the position detector, thereby achieving higher repeatability measurement accuracy of film thickness.

Description

Technical Field

[0001] This invention relates to the field of testing, and more particularly to a photoacoustic measuring device and a method for measuring film thickness. Background Technology

[0002] The existing photoacoustic measurement mechanism is mainly based on the following: a short-pulse laser irradiates the surface of a membrane sample, causing the sample to absorb photons and undergo thermoelastic deformation, forming a deformation zone on the surface; the thermoelastic deformation generates sound waves that propagate on and within the solid surface; the longitudinal sound waves propagate to the interface (specifically, the junction between the substrate and membranes), generating the first echo signal; the first echo signal reaches the upper surface, further altering the deformation morphology; the echo signal bounces off the upper surface and then bounces back to the interface, generating a second echo signal; the second echo signal reaches the upper surface, causing the bulge morphology to change again, and the echo signal may include more than three echoes. The time interval between the echoes reaching the upper surface can be obtained through a detection system, from which the membrane sample thickness can be calculated.

[0003] Existing detection systems can only detect changes in material reflectivity. When the material itself has a small change in reflectivity (such as inert metal material Cu), or when the material structure or surface roughness changes (such as when the surface roughness of a metal material is large after CMP chemical mechanical polishing, or Cu linear arrays, etc.), the change in material reflectivity is on a low order of magnitude, and it is impossible to obtain a high signal-to-noise ratio photoacoustic signal that can be used to extract film thickness information.

[0004] Therefore, it is necessary to provide a novel photoacoustic measurement device and film thickness measurement method to solve the above-mentioned problems existing in the prior art. Summary of the Invention

[0005] The purpose of this invention is to provide a method that directly measures the displacement of the light beam at the pupil caused by the deflection of the light beam by adding a position sensitive detector / device (PSD) to the detection optical path, thereby obtaining the time for the echo to reach the upper surface and calculating the film thickness value.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a photoacoustic measurement device, comprising 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;

[0007] The excitation light is projected onto the measurement area of ​​the object under test along the excitation light optical path, and the detection light is projected onto the measurement area along the detection light optical path; the detection component includes a one-dimensional position sensor or a two-dimensional position sensor for receiving the detection beam reflected by the object under test, so as to obtain at least the offset of the reflected detection beam, wherein the one-dimensional position sensor and the two-dimensional position sensor can be switched or replaced.

[0008] The image acquisition component is used to acquire images of the light spots of the excitation light and the probe light on the surface of the object under test; the controller is used to receive the images to determine the relative positions of the excitation light spot and the probe light spot on the surface of the object under test, and to control the detection component to select the one-dimensional position sensor or the two-dimensional position sensor according to the relative positions; the controller is also used to acquire the test parameters of the object under test according to the output signal of the detection component.

[0009] By incorporating a designed position sensor, materials with low reflectivity can obtain photoacoustic signals with higher signal-to-noise ratios, thereby achieving higher accuracy in repeatable film thickness measurements and enhancing system robustness. Furthermore, selecting the appropriate position sensor based on the relative orientation of the pump light and probe light spots during measurement further improves the accuracy of the acquired offset and enhances the signal-to-noise ratio.

[0010] 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 selects the 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;

[0011] If the relative orientation is not along the x-direction or 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 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; wherein, the x-direction and y-direction are two orthogonal directions within the surface of the object being measured. In a further embodiment, the one-dimensional position sensor includes two output terminals, and the two-dimensional position sensor includes four output terminals;

[0012] The detection surface of the one-dimensional position sensor is a rectangular photosensitive surface or is composed of two square photosensitive surfaces of the same size; the detection surface of the two-dimensional position sensor is a square photosensitive surface or is composed of four square photosensitive surfaces of the same size distributed in a 2×2 array.

[0013] A further embodiment discloses a photoacoustic measurement device that obtains the offset δ from the output signal of the one-dimensional position sensor, comprising:

[0014]

[0015] Wherein, I1 and I2 are the output signals of the two output terminals of the one-dimensional position sensor, and L is the effective distance between the two output terminals or the diameter of the reflected detection beam.

[0016] A further disclosed embodiment of the photoacoustic measuring device obtains the offset δ from the output signal of the two-dimensional position sensor, including:

[0017]

[0018] Where, δ x and δ y Let I1, I2, I3, and I4 be the components of the offset δ in the x and y directions, respectively. Let I1, I2, I3, and I4 be the output signals of the four output terminals of the two-dimensional position sensor. Let I1 and I2, I3 and I4 be the output signals of two adjacent output terminals corresponding to the y direction, and let I1 and I4, I2 and I3 be the output signals of two adjacent output terminals corresponding to the x direction. x L represents the effective distance between the two output terminals corresponding to output signals I1 and I4, or the diameter of the reflected detection beam. y The effective distance between the two output terminals corresponding to output signals I1 and I2, respectively, or the diameter of the reflected detection beam.

[0019] In some embodiments, a photoacoustic measurement device is disclosed, wherein the detection component further includes a photodetector to obtain the change in light intensity caused by the change in the reflectivity of the measured object;

[0020] The reflected detection beam is received by the photodetector and the one-dimensional position sensor or the two-dimensional position sensor after passing through the beam splitter.

[0021] In some embodiments, a photoacoustic measurement device is further disclosed, wherein the reflected probe beam is received by the photodetector after passing through an imaging unit, and the magnification of the imaging unit is 1:1; the probe beam received by the one-dimensional position sensor or the two-dimensional position sensor is a parallel beam.

[0022] In one possible embodiment, the disclosed photoacoustic measurement device determines the beam splitting ratio of the beam splitting component by the saturation power of the one-dimensional position sensor or the two-dimensional position sensor and the photodetector, and the power of the probe light received by the one-dimensional position sensor, the two-dimensional position sensor, and the photodetector reaches the saturation power. By using the photodetector, it is possible to switch arbitrarily between two measurement modes, material reflectivity measurement and bulge deflection measurement, to select a measurement method with greater responsivity for different measurement conditions, thereby obtaining a higher signal-to-noise ratio and system repeatability accuracy.

[0023] In a second aspect, the present invention also provides a film thickness measurement method, the measurement method being applied to the photoacoustic measurement device of the first aspect mentioned above, comprising: acquiring the output signal of the detection component under different time delays of the excitation light and the detection light;

[0024] The controller controls the optical delay device to adjust the optical path difference between the excitation light and the probe light, so as to achieve the adjustment of different time delays. The optical delay device is set in the excitation light optical path and / or the probe light optical path.

[0025] Based on the output signal, a detection signal is obtained, the detection signal including the detection beam offset, or including the detection beam offset and the light intensity change caused by the change in the reflectivity of the object being measured;

[0026] The time interval of the detection signal in the time domain is obtained, and the film thickness of the test object is obtained based on the time interval.

[0027] A further disclosed embodiment of the measurement method, which obtains the film thickness of the object under test based on the time interval, includes: obtaining a first time interval based on the probe beam offset, and calculating a first film thickness;

[0028] The second time interval is obtained based on the change in light intensity caused by the change in reflectivity of the object under test, and the second film thickness is calculated.

[0029] The obtained first film thickness or second film thickness is taken as the film thickness of the test object; or...

[0030] The average of the first film thickness and the second film thickness is taken as the film thickness of the test object.

[0031] For details regarding the beneficial effects of the second aspect, please refer to the description in the first aspect above. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the detection component architecture according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the detection component structure according to an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the detection component structure according to an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram illustrating an embodiment of a photoacoustic measurement device according to the present invention;

[0036] Figure 5 This is a schematic diagram of the basic framework of the photoacoustic detection principle of this invention;

[0037] Figure 6 This is a schematic diagram illustrating an embodiment of a photoacoustic measurement device according to the present invention;

[0038] Figure 7 This is a schematic diagram illustrating an embodiment of a photoacoustic measurement device according to the present invention;

[0039] Figure 8 These are schematic diagrams of several embodiments of the position sensor of the present invention;

[0040] Figure 9 This is a schematic diagram of the film thickness measurement method of the present invention.

[0041] Reference numerals: 000-Laser; 120-Beam splitter; 130-Chopper; 140-Beam combiner; 210-First reflector; 220-Optical delayer; 230-Second reflector; 250-First condenser; 270-Second condenser; 260-Collimator; 300-Square beam splitter; 310-First beam splitter; 320-Second beam splitter; 400-Position sensor; 420-Photodetector; 410-First lock-in amplifier; 411-Second lock-in amplifier; 800-Object under test; 810-Sample surface bulge; 510-Excitation beam; 520-Detector beam; 500-Image acquisition component; 610-One-dimensional position sensor; 620-Two-dimensional position sensor. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be described below with reference to the accompanying drawings. In the description of the embodiments of the present invention, the terminology used in the following embodiments is for the purpose of describing specific embodiments only and is not intended to be a limitation of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “the,” “the,” “the,” and “this” are intended to also include expressions such as “one 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 (including two). The term “and / or” is used to describe the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character “ / ” generally indicates that the preceding and following related objects are in an “or” relationship.

[0043] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized. The term "connection" includes direct connections and indirect connections, unless otherwise stated. "First" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0044] In embodiments of the present invention, the terms "exemplarily" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplarily" or "for example" in embodiments of the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the terms "exemplarily" or "for example" is intended to present the relevant concepts in a specific manner.

[0045] Embodiments of the present invention provide a photoacoustic measurement device, such as... Figure 4 As shown, the light emitted by laser 000 is split into an excitation beam 510 and a probe beam 520 by beam splitter 120. The excitation beam path is equipped with a chopper 130, and the probe beam path is equipped with a first emitting mirror 210, an optical delay unit 220, and a second reflecting mirror 230. The excitation beam 510 and probe beam 520 are combined by beam combiner 140 and then focused onto the surface of the test object 800 by a second condenser mirror 270. The probe light reflected from the sample surface is received by the detection component. The detection component includes a position sensor 400 and a lock-in amplifier 410. The structure of the detection component can adopt any of the technical solutions in the embodiments of this invention. For example, it can adopt the structure shown in the attached figure. Figure 1-3 The diagram shows the structural configuration of the detection component; different structural configurations of the detection component are replaceable or switchable. This is achieved by adding a PSD (position sensor) at the pupil of the detection optical path. Figure 4 At 400°, the beam displacement at the pupil caused by the deflection of the probe beam at 520° is directly measured, thereby obtaining the echo arrival time at the upper surface and calculating the film thickness. The beam deflected by the bulge generated on the surface of the object under test (800°) is collimated into parallel light by the collimating lens 260°. The collimating lens... Figure 4 A PSD position-sensitive sensor 400 is placed on the rear focal plane of the 260mm lens.

[0046] For example, such as Figure 5 As shown, the excitation and probe beams are focused onto the surface of the object under test by a condenser lens. After the excitation light induces photoacoustic interaction, the sound waves generated by the photoacoustic interaction propagate between the film layers and reach the interface between the top material and the air. Due to stress and strain, local bulges on the material surface at the picometer level are caused—sample surface bulges 810. At this time, the incident probe light converges to the position where the surface tilt is large due to the bulge, which is the position where the first derivative / gradient of the bulge morphology is the maximum. Generally, there is a micrometer-level positional offset between the focus center of the probe light and the excitation light. The specific offset is related to the spot morphology, energy distribution and spot size of the excitation light. The collimating optical element is located between the measurement area and the position sensor 400. The reflected probe light beam is collimated by the collimating lens 260 and then received by the position sensor 400.

[0047] The sound waves generated by photoacoustic interaction propagate longitudinally and are reflected back to the sample surface at the interface. Before the sound waves reach the surface, the light rays are reflected by the sample surface, generally approximating specular reflection. The light rays propagate along the path indicated by the dashed lines (see...). Figure 5 When the sound wave generated by photoacoustic action reaches the sample surface, the sample surface will produce local surface protrusions again. The PSD400 directly obtains the offset of the probe beam, and then obtains the time when the echo reaches the upper surface of the sample to calculate the film thickness.

[0048] The surface protrusion causes the surface where the probe light focal point is located to tilt. Assuming the tilt angle of the sample surface protrusion is θ, the reflected light is deflected by 2θ. The resulting offset δ can be expressed by the following formula: δ=f×tan2θ——Formula 1;

[0049] Where f is the focal length of collimating lens 260, the offset δ can be measured by placing a position-sensitive sensor 400 on the back focal plane of collimating lens 260. Given the focal length f of collimating lens, the bulge tilt angle θ can be further obtained.

[0050] In some disclosed embodiments, the photoacoustic measuring device, such as Figure 6 As shown, the detection component includes a photodetector 420 and a position sensor 400. The photoacoustic measurement device also includes a beam splitter 300. After the detection beam passes through the beam splitter, 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.

[0051] In some embodiments, the light beam is deflected by a bulge generated on the surface of the sample under test, such as... Figure 6As shown, the light is collimated into parallel light by the collimating lens. A flat beam splitter 300 is placed behind the collimating lens 260. The specific placement position of the flat beam splitter 300 can be near the rear focal plane of the collimating lens 260. The specific splitting ratio can be designed and adjusted according to the saturation power of the two detectors. Here, the default splitting ratio is 50:50, so that the power of the light signal received by the photodetector 420 and the position sensor 400 is close to their respective saturation power.

[0052] The beam splitter 300 divides the light beam into two: one beam is focused onto the photodetector 420 by the focusing lens 250 to measure changes in material reflectivity; the other beam is directly incident on the photosensitive surface of the PSD position sensor 400 to measure the deflection caused by bulging. Both measurement modes can obtain the echo arrival time on the upper surface, which can be used to calculate the film thickness value of the measured object surface. The choice of measurement method depends on the material, surface roughness, and geometry of the sample. The application of two measurement modes improves the versatility of the measurement equipment, enabling film thickness measurement of different materials. It also provides a high signal-to-noise ratio and higher accuracy in film thickness acquisition across various measurement scenarios.

[0053] In other embodiments, the photoacoustic measuring device includes the beam-splitting optical element as specifically as follows: Figure 6 The square beam splitter 300 in the structure is used to split the detection beam into two parts. One part is received by the detection component, and the other part is reflected by the square beam splitter 300 and received by the position sensor. The first lock-in amplifier is used to receive the signal outputs of the detection component and the position sensor, respectively. The system can switch arbitrarily between two measurement modes to select the measurement method with greater responsiveness for different measurement conditions, thereby obtaining a higher signal-to-noise ratio and system repeatability accuracy.

[0054] In other embodiments, the photoacoustic measuring device, such as Figure 7 As shown, two measurement modes can be achieved through the 300 in the spectrometer and the subsequent detection device. The two sets of signals generated can be connected to the signal input terminals of the dual-channel lock-in amplifier, or 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 410 or 411 respectively. The system can switch between the material reflectivity measurement mode and the deflection measurement mode through the control program.

[0055] In reflectivity mode, collimating lens 260 and condenser lens 270 form a Keplerian beam expander system to image the test object 800. The focused spot size is typically between several and tens of micrometers. If a 1:1 magnification system is used, the spot size on the detector / image plane is consistent with the spot size on the sample surface. In this case, the size of the photosensitive surface is generally on the order of millimeters. Even if the beam is partially deflected due to system vibration, environmental disturbances, or sample bulging, according to the imaging principle, the position and size of the spot on the imaging plane will not change. Therefore, the signal magnitude is unaffected by these disturbances, exhibiting good robustness. For most materials, such as W and Mo, photoacoustic signal measurement can be performed using reflectivity measurement mode. For some materials, such as Cu, metal film surfaces with high roughness after CMP, or special structures like Cu lines, the amplitude of reflectivity signal changes is low; therefore, deflection measurement mode is used for photoacoustic signal measurement.

[0056] In deflection mode, a strong signal amplitude can be obtained for most materials, thus adapting to most operating conditions. However, any noise source that affects the beam direction will negatively impact the deflection data, such as the stability of the light source's pointing and the mechanical vibration of individual mirrors. Depending on the system's specific requirements, such as the performance of the femtosecond laser and the type of material being measured, the two measurement modes can be switched.

[0057] In some embodiments, the photoacoustic measuring device, such as Figure 7 As shown, the photoacoustic measuring device further includes a first focusing optical element, specifically as follows: Figure 7 The first condenser lens 250 is located between the beam splitter 300 and the photodetector 420, and the collimating optical element 260 is located between the measurement area of ​​the object under test 800 and the beam splitter 300.

[0058] In some embodiments, the photoacoustic measuring device, such as Figure 7 As shown, the photoacoustic measuring device also includes a light source component, specifically as follows: Figure 7 The laser 000 and the beam splitting optical components are as follows: Figure 7 The beam splitter 120, the light source component, provides a source beam. After passing through the beam-splitting optical component, the source beam is divided into two parts: one part is the excitation beam 510, and the other part is the probe beam 520. The photoacoustic measurement device also includes a beam-combining optical component, specifically as follows: Figure 7 The beam combiner 140, the beam combining optical component, is used to combine the excitation beam and the probe beam into one, and project the combined beam onto the measurement area of ​​the object under test, specifically as follows: Figure 7 The tested object is 800.

[0059] In some embodiments, the photoacoustic measuring device, such as Figure 7 As shown, the photoacoustic measurement device also includes a chopper optical component, specifically as follows: Figure 7 The chopper 130 is located in the excitation light path of the optical chopper component, specifically as follows: Figure 7 Between the beam splitter 120 and the beam combiner 140, the excitation beam, after passing through the chopping optical component, is received by the beam combiner 140. The optical chopping component is used to modulate the excitation beam. The chopper can be an acousto-optic modulator or an electro-optic modulator. The system also includes an optical delayer 220 disposed in the probe light path. The optical delayer 220 is located between the beam splitter 120 and the beam combiner 140. After passing through the optical delayer 220, the probe beam is received by the beam combiner 140. The optical delayer 220 is used to generate a phase delay in the probe beam. A first reflector 210 and a second reflector 230 are also disposed in the probe light path. The first reflector 210 is located between the beam splitter 120 and the optical delayer 220, and the second reflector 230 is located between the optical delayer 220 and the beam combiner 140.

[0060] The photoacoustic measurement device provided in the above embodiments also includes a controller and an image acquisition component. Figure 4 , 6 (Not shown in -7), the detection component includes a one-dimensional position sensor or a two-dimensional position sensor for receiving the detection beam reflected by the object under test, so as to obtain at least the offset of the reflected detection beam, wherein the one-dimensional position sensor and the two-dimensional position sensor can be switched or replaced; the image acquisition component is used to acquire images of the excitation light and the detection light spots on the surface of the object under test; the controller is used to receive the images to determine the relative orientation of the excitation light spot and the detection light spot on the surface of the object under test. It can be understood that the relative orientation is the direction from the centroid of one spot to the centroid of another spot on the surface of the object under test. The controller can obtain the centroids of the two spots respectively based on the images of the excitation light spot and the detection light spot, and thus determine the relative orientation.

[0061] The detection component includes a one-dimensional position sensor 610, such as Figure 1 or Figure 2 As shown; the detection component can also be configured to include a two-dimensional position sensor 620, such as Figure 3 As shown.

[0062] Based on the relative orientation, the controller controls the detection component to select either the one-dimensional position sensor 610 or the two-dimensional position sensor 620; that is, based on the relative orientation, the detection component is configured as follows: Figure 1 Or the two one-dimensional position sensors 610 shown in Figure 2, or configured as follows: Figure 3 A two-dimensional position sensor 620 is shown; as shown Figure 1As shown, two one-dimensional position sensors 610 are provided, wherein the directions of the long sides of the detection surfaces of the two one-dimensional position sensors are orthogonal to each other; the controller is also used to acquire the measured parameters of the object under test based on the output signal of the detection component. The technical effect of selecting the corresponding PSD based on the relative orientation is that it can select a suitable PSD according to the direction of the offset, improving the accuracy of acquiring the offset and increasing the signal-to-noise ratio. At the same time, considering the bandwidth and accuracy of different PSDs, it adapts to different measurement needs, ensuring measurement accuracy and efficiency under different working conditions. In actual measurement, the solution provided by the above embodiment enables the PSD to accurately match the deflection direction of the detection beam, thereby further improving the acquired offset of the detection beam and improving measurement accuracy.

[0063] 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 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 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 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.

[0064] It is understandable that the coordinate system of the detection surface of the detection component corresponds to the coordinate system of the surface of the object being measured, as shown in the attached figure. Figure 4 As shown, a local coordinate system O-XYZ is established on the surface of the object under test 800, where the x and y directions are two mutually orthogonal directions within the surface of the object under test, and z is the direction perpendicular to the surface of the object under test. A coordinate system O'-X'Y'Z' is established on the detection surface of the detection component, 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 of the object under test 800 acquired by the image acquisition component 500 are used to obtain the relative orientation of the two spots in the local coordinate system O-XYZ. Taking the direction from the centroid of the detection light spot to the centroid of the excitation light spot as an example, it can be X+ / X- / Y+ / Y-. The detection beam behind the collimating lens will be deflected in the local coordinate system O'-X'Y'Z' of the PSD, corresponding to X'+ / X'- / Y'+ / Y'-. By selecting a matching PSD device design according to different relative orientations, beam deflection information and film thickness information can be obtained, improving the accuracy of the acquired detection beam offset.

[0065] The relative orientation is along x(X+ / X-) or y(Y+ / Y-), and 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, i.e., it can be... Figure 1 The detection component shown includes two one-dimensional position sensors, or it could include a single position sensor (not shown in the figure). The relative orientation is not along the x or y direction. After the detection light is split, it is received by two one-dimensional PSDs. The two one-dimensional PSDs respectively acquire the components of the offset in two orthogonal directions, thus obtaining the actual offset.

[0066] In some embodiments, the relative orientation is not along the x or y direction, and the offset of the reflected probe light can be obtained by a two-dimensional position sensor, such as... Figure 3 As shown, the reflected probe light 520 has a first beam splitter 310 set in its propagation path. After passing through the first beam splitter 310, a portion of the probe light is reflected by the first beam splitter 310 to the image acquisition unit 500 to obtain an image of the probe light spot. The probe light that has been transmitted through the first beam splitter 310 continues to propagate and is received by a two-dimensional position sensor 620. In addition, the image acquisition unit 500 also receives the excitation light beam to obtain an image of the excitation light spot.

[0067] In one possible embodiment, it can be targeted at such as Figure 1 The detection component structure shown or as Figure 3 The detection component structure shown is improved by incorporating a photodetector into the detection system to receive partially reflected detection beams, enabling the detection component to also detect changes in the reflectivity of the object's surface. For example, regarding... Figure 1 The detector component structure shown has been improved as follows: Figure 2 As shown, during its propagation, the reflected probe light 520 passes through the first beam splitter 310. A portion of the beam is reflected by the first beam splitter 310 to the image acquisition unit 500 to obtain an image of the probe light spot. The probe light transmitted through the first beam splitter 310 propagates to the second beam splitter 320. The probe light reflected by the second beam splitter 320 is received by the photodetector 420. The transmitted probe light is split into two parts after passing through the square beam splitter 300, and is received by two one-dimensional position sensors 610 respectively. In addition, the image acquisition unit also receives the excitation light beam to obtain an image of the excitation light spot. Similarly, the above... Figure 2 Publicly available photodetectors can also be applied to Figure 3 The detection component is shown. Clearly, the detection component structures disclosed in the above embodiments can all be applied to photoacoustic measurement equipment.

[0068] Based on the relative positions of the actual focusing position of the probe beam and the focusing position of the excitation beam in the local coordinate system O-XYZ of the sample, the centroid of the probe beam will deflect in different directions in the local coordinate system O'-X'Y'Z' of the PSD, which can be X'+ / X'- / Y'+ / Y'-. When the probe beam spot is at the positive X position X+ of the excitation beam spot, the deflection direction of the probe beam in the local coordinate system of the PSD is the positive X' position X'+; when the probe beam spot is at the negative X position X- of the excitation beam spot, the deflection direction of the probe beam in the local coordinate system of the PSD is the negative X' position X'-; a similar situation applies to the Y direction.

[0069] In one possible embodiment, in the photoacoustic measurement device, if the relative orientation is not along the x-direction or 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 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.

[0070] In some embodiments, the photosensitive surface of the PSD sensor in the photoacoustic measuring device has several variations, such as... Figure 8 As shown, one embodiment comprises a photodetector element with a square / rectangular photosensitive surface; another embodiment comprises two photodetector elements with square photosensitive surfaces of equal size arranged side-by-side in an axially symmetrical configuration; yet another embodiment comprises four photodetector elements with square photosensitive surfaces of equal size arranged in a centrally symmetrical configuration. Different PSD design schemes can be applied to different measurement scenarios, while simultaneously considering the detection accuracy and response speed of the position sensor. Furthermore, during the measurement process, based on the actual direction / relative orientation of the probe beam deflection, the device automatically selects / matches a suitable layout of the detection components, further improving the detection accuracy of the probe beam deflection, thereby improving the signal-to-noise ratio of photoacoustic measurement and the measurement accuracy of film thickness.

[0071] In some embodiments of this application, the present invention also discloses a photoacoustic measurement device, wherein the one-dimensional position sensor 610 includes two output terminals, and the two-dimensional position sensor 620 includes four output terminals; the detection surface of the one-dimensional position sensor 610 is a rectangular photosensitive surface, such as... Figure 8 Situation B in the above example could be composed of two identical square photosensitive surfaces, such as... Figure 8 In scenario C; the detection surface of the two-dimensional position sensor 620 is a square photosensitive surface, as shown in... Figure 8 Case A in the diagram could be composed of four identical square photosensitive surfaces arranged in a 2×2 array, as shown in the diagram. Figure 8 Situation D in the above.

[0072] In further embodiments of this application, the photoacoustic measuring device obtains the offset δ from the output signal of the one-dimensional position sensor 610, including:

[0073]

[0074] Wherein, I1 and I2 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. Two photosensitive surface structures Figure 8 As shown in Figure C, L is the diameter of the light spot on the detection surface (the diameter of the reflected detection beam), which allows for more accurate calculation. The light spot diameter is the diameter in this direction, which is the length direction of the rectangular photosensitive surface in the one-dimensional position sensor 610, i.e. Figure 8 The X direction, as shown in C, or the length direction of the rectangular photosensitive surface formed by two squares of the same size in the one-dimensional position sensor 610. The PSD of a single rectangular photosensitive surface. Figure 8 As shown in Figure B, L is the effective distance between the photocurrent output terminals, which allows for more accurate calculation.

[0075] In some embodiments of this application, the photoacoustic measuring device obtains the offset δ from the output signal of the two-dimensional position sensor 620, including:

[0076]

[0077] Where, δ x and δ y Let I1, I2, I3, and I4 be the components of the offset δ in the x and y directions, respectively. Let I1, I2, I3, and I4 be the output signals of the four output terminals of the two-dimensional position sensor. Let I1 and I2, I3 and I4 be the output signals of two adjacent output terminals corresponding to the y direction, and let I1 and I4, I2 and I3 be the output signals of two adjacent output terminals corresponding to the x direction. x L represents the effective distance between the two output terminals corresponding to output signals I1 and I4, or the diameter of the reflected detection beam. y The effective distance between the two output terminals corresponding to output signals I1 and I2, respectively, or the diameter of the reflected detection beam.

[0078] In one possible embodiment of this application, the photoacoustic measuring device further includes a photodetector 420 in the detection component to acquire the light intensity change caused by the change in reflectivity of the object under test; the reflected detection beam is received by the photodetector 420 and the one-dimensional position sensor 610 or the two-dimensional position sensor 620 after passing through a beam splitter. In a further embodiment of the photoacoustic measuring device, 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 under test is the same as the spot size on the detection surface of the photodetector.

[0079] The detection light received by the one-dimensional or two-dimensional position sensor is a parallel beam. Specifically, a matching PSD device design is selected based on the different deflection directions of the detection beam. Both positive and negative offsets in the X' direction can be measured. A device must be selected that can transmit the photocurrent differential signal to feedback the offset δ of the detection beam's centroid in the X' direction. X’ The PSD design scheme is used to calculate the sample surface tilt angle θ using the above formula 1. At the same time, the film thickness can be calculated based on the time position of the reflectivity change caused by light deflection in the differential signal. The calculation principle here is the same as the material reflectivity echo calculation method.

[0080] In some embodiments of this application, the PSD detector design selection mainly considers two aspects: position detection sensitivity / accuracy; and detector bandwidth. For the same detector material, generally, the larger the photosensitive surface area, the larger the junction capacitance of the photodetector, and the smaller the bandwidth. Simultaneously, the saturation light power that the detector can receive also increases with the increase of the photosensitive area, and the signal-to-noise ratio of the photoelectric signal also increases accordingly. Furthermore, as the acceptable light spot area increases, the PSD position detection accuracy also increases. A suitable PSD detector design can be selected based on the actual operating conditions' requirements for detection bandwidth and detection position accuracy.

[0081] In other embodiments, the specific design scheme of the PSD is as follows: Figure 8 In section A, a two-dimensional position sensor is composed of a square photodetector element with a photosensitive surface. The length of the PSD in the x-direction is Lx, and its length in the y-direction is Ly, where Ly = Lx. A single detector surface has a pin at each of its four corners to guide the photocurrent. This pin detects the magnitude of the beam translation in the X / Y directions, and then calculates the beam angular deflection and the time of deflection. The specific conversion formulas between the current and the beam translations δx and δy in the x and y directions can be expressed as follows: Where 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 terminals.

[0082] In other embodiments, the specific design scheme of the PSD is as follows: Figure 8 In section B, a one-dimensional position sensor is formed by a photodetector element with a narrow rectangular photosensitive surface. The length of the device in the x-direction, Lx, is greater than Ly, and it can detect the centroid shift of the beam in the x-direction. Rotating this design by 90 degrees yields a photodetector element with a rectangular photosensitive surface in the y-direction, where the length of the device in the x-direction, Ly, is greater than Lx, and it can detect the centroid shift of the beam in the y-direction.

[0083] A single detector surface has two pins in the X direction that derive the photocurrent. The specific formula for converting the current into the beam's translation δ in the X direction can be expressed as follows: 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 specific formula for converting the current to the beam translation δ 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.

[0084] In other embodiments, the specific design scheme of the PSD is as follows: Figure 8 In case C, the sensor is a one-dimensional position sensor: it consists of two photodetector elements with square photosensitive surfaces of equal size, capable of detecting the centroid shift of the beam in the X direction. Rotating this design by 90 degrees yields a dual photodiode design in the Y direction, which can also detect the centroid shift of the beam in the Y direction.

[0085] The difference between the photocurrent values ​​I1 and I2 obtained from photosensitive surfaces 1 and 2 can be used to detect the magnitude of the beam translation in the X direction, thereby calculating the beam angle deflection and the time of deflection. Specifically, the conversion formula between current and beam translation δ in the X direction can be expressed as follows: Where L is the diameter of the light spot in the x-direction. In the y-direction design, the specific formula for converting the current to the beam translation δ in the y-direction can be expressed as: Where L is the diameter of the light spot in the y direction.

[0086] In other embodiments, the specific design scheme of the PSD is as follows: Figure 8 In scenario D, a two-dimensional position sensor is used: four detection surfaces are arranged in a 2×2 array, with a pin at each of the four corners to guide the photocurrent. The sensor detects the magnitude of the beam translation in the X / Y directions, and then calculates the beam angle deflection and the time of deflection. The difference between the photocurrent and photovoltage values ​​obtained from detection photosensitive surfaces 1, 2, 3, and 4 can be used to detect the magnitude of the beam translation in the X / Y directions, and then calculate the beam angle deflection and the time of deflection. The specific conversion formulas between the current and the beam translations δx and δy in the x and y directions can be expressed as follows: Where 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.

[0087] PSD design such as Figure 8 Chinese B, PSD design such as Figure 8 Both C1 and C2 are single-direction position detection designs, capable of measuring the deflection of the bulge in one direction. Alternatively, a combination of two can be used to detect deflection in any direction. This simplified design reduces the requirements for subsequent circuit design, making it easier to implement and lower in cost. For example... Figure 8 The design scheme of China B is relatively similar to Figure 8 The C-type design has a large photosensitive surface area, large junction capacitance, and large photocurrent, resulting in high positioning accuracy, but the device bandwidth is low.

[0088] PSD design such as Figure 8 Chinese A and PSD design, such as Figure 8 The D-type sensor can detect the position in both the X and Y directions and measure the deflection of the bulge in both directions. It can detect deflection in any direction, which reduces the relative orientation requirements of the excitation and detection light spots. It can be used in both the X and Y directions, which enhances the flexibility of the equipment and has a high degree of system integration, but it requires higher requirements for subsequent circuit design.

[0089] The present invention also provides a method for measuring film thickness, such as... Figure 9 As shown, the film thickness measurement method is applied to the photoacoustic measurement device disclosed in the foregoing embodiments, including:

[0090] Step 100: Obtain the output signals of the detection component under different time delays for the excitation light and the detection light;

[0091] Step 200: The controller controls the optical delay device to adjust the optical path difference between the excitation light and the probe light to achieve different time delays. The optical delay device is set in the excitation light optical path and / or the probe light optical path.

[0092] Step 300: Based on the output signal, obtain a detection signal, the detection signal including the detection beam offset, or including the detection beam offset and the light intensity change caused by the change in the reflectivity of the object being measured;

[0093] Step 400: Obtain the time interval in the time domain of the detection signal, and obtain the film thickness of the test object based on the time interval.

[0094] In a further embodiment of the film thickness measurement method, obtaining the film thickness of the object under test based on the time interval includes:

[0095] Step 1000: Based on the probe beam offset, obtain the first time interval and calculate the first film thickness;

[0096] Step 2000: Based on the change in light intensity caused by the change in reflectivity of the measured object, obtain the second time interval and calculate the second film thickness;

[0097] Step 3000: Take the obtained first film thickness or second film thickness as the film thickness of the test object; or, take the average value of the obtained first film thickness and second film thickness as the film thickness of the test object.

[0098] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A photoacoustic measuring device, characterized in that, include: Light emitter, controller, image acquisition unit, and detection unit; The light emitter is used to generate excitation light and probe light; The excitation light is projected onto the measurement area of ​​the object under test along the excitation light optical path, and the probe light is projected onto the measurement area along the probe light optical path; The detection component includes a one-dimensional position sensor or a two-dimensional position sensor for receiving the detection beam reflected by the object under test, so as to obtain at least the offset of the reflected detection beam. The one-dimensional position sensor and the two-dimensional position sensor can be switched or replaced. The image acquisition component is used to acquire images of the light spots of the excitation light and the probe light on the surface of the object under test; The controller is used to receive the image to determine the relative orientation of the excitation light spot and the probe light spot on the surface of the object being measured, and to control the detection component to select the one-dimensional position sensor or the two-dimensional position sensor based on the relative orientation. The controller is also used to obtain the test parameters of the object under test based on the output signal of the detection component.

2. The photoacoustic measuring device as described in claim 1, characterized in that, Based on the relative orientation, controlling the detection component to select either the one-dimensional position sensor or the two-dimensional position sensor includes: If the relative orientation is along the x-direction or 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 or 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 and y directions 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. Wherein, the x-direction and the y-direction are two mutually orthogonal directions within the surface of the object being measured.

3. The photoacoustic measuring device as described in claim 2, characterized in that, 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 is composed of two square photosensitive surfaces of the same size; the detection surface of the two-dimensional position sensor is a square photosensitive surface or is composed of four square photosensitive surfaces of the same size distributed in a 2×2 array.

4. The photoacoustic measuring device as described in claim 3, characterized in that, The offset δ is obtained from the output signal of the one-dimensional position sensor, including: Wherein, I1 and I2 are the output signals of the two output terminals of the one-dimensional position sensor, and L is the effective distance between the two output terminals or the diameter of the reflected detection beam.

5. The photoacoustic measuring device as described in claim 3, characterized in that, The offset δ is obtained from the output signal of the two-dimensional position sensor, including: Where, δ x and δ y Let I1, I2, I3, and I4 be the components of the offset δ in the x and y directions, respectively. Let I1, I2, I3, and I4 be the output signals of the four output terminals of the two-dimensional position sensor. Let I1 and I2, I3 and I4 be the output signals of two adjacent output terminals corresponding to the y direction, and let I1 and I4, I2 and I3 be the output signals of two adjacent output terminals corresponding to the x direction. x L represents the effective distance between the two output terminals corresponding to output signals I1 and I4, or the diameter of the reflected detection beam. y The effective distance between the two output terminals corresponding to output signals I1 and I2, respectively, or the diameter of the reflected detection beam.

6. The photoacoustic measuring device according to any one of claims 1-5, characterized in that, The detection component also includes a photodetector to obtain the change in light intensity caused by the change in the reflectivity of the object being measured. The reflected detection beam is received by the photodetector and the one-dimensional position sensor or the two-dimensional position sensor after passing through the beam splitter.

7. The photoacoustic measuring device as described in claim 6, characterized in that, The reflected detection beam is received by the photodetector after passing through the 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 beam.

8. The photoacoustic measuring device as described in claim 6, characterized in that, The beam splitting ratio of the beam 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 power of the probe light received by the one-dimensional position sensor, the two-dimensional position sensor and the photodetector reaches the saturation power.

9. A method for measuring film thickness, characterized in that, The film thickness measurement method is applied to the photoacoustic measurement device as described in any one of claims 1-8, comprising: The output signals of the detection component are acquired under different time delays for the excitation light and the detection light; The controller controls the optical delay device to adjust the optical path difference between the excitation light and the probe light, so as to achieve the adjustment of different time delays. The optical delay device is set in the excitation light optical path and / or the probe light optical path. Based on the output signal, a detection signal is obtained, the detection signal including the detection beam offset, or including the detection beam offset and the light intensity change caused by the change in the reflectivity of the object being measured; The time interval of the detection signal in the time domain is obtained, and the film thickness of the test object is obtained based on the time interval.

10. The film thickness measurement method as described in claim 9, characterized in that, Obtaining the film thickness of the test object based on the time interval includes: Based on the probe beam offset, the first time interval is obtained, and the first film thickness is calculated. The second time interval is obtained based on the change in light intensity caused by the change in reflectivity of the object under test, and the second film thickness is calculated. The obtained first film thickness or second film thickness is taken as the film thickness of the test object; or... The average of the first film thickness and the second film thickness is taken as the film thickness of the test object.

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