Metrology device and a method for non-destructive metrology of a sample

Abstract

A time-resolved reflectivity meter uses a pulsed pump beam and a pulsed probe beam to image the structure of an underlying layer, with at least a time delay between the pulses. One or both of the beams are modulated. A camera having a multi-pixel array and independent phase-locked positioning for each pixel in the multi-pixel array receives and demodulates the reflectivity probe beam to generate an image. The camera can record changes in reflectivity or surface deformation of the target sample at each pixel based on at least one time delay between the pump pulse and the probe pulse, which can characterize at least one property of the target sample.

Description

Technical Field

[0001] The subject matter described herein relates generally to microscopy, and more particularly to the use of time-resolved reflectivity measurements. Cross-reference to related applications

[0002] This application claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 63 / 495,034, filed on April 7, 2023, and entitled “A SYSTEM AND METHOD FOR FAST MICROSCOPY,” which is assigned to the assignee of this application and is incorporated herein by reference in its entirety. Prior Art

[0003] Semiconductor processing for forming integrated circuits requires a series of processing steps. These steps include the deposition and patterning of material layers, such as insulating layers, polysilicon layers, and metal layers. These material layers are typically patterned using a photoresist layer, which is patterned over the material layer using a mask or reticle. Typically, the mask has alignment targets or keys that align with fiducial marks formed in previous layers on the substrate. Overlay and alignment of lithographically defined patterns on top of underlying patterns are fundamental to device operation in all multi-layer patterning process flows. Misalignment between layers or patterns can lead to device failure.

[0004] Various optical techniques and specially designed targets are conventionally used for alignment and overlay measurement. For example, conventional imaging techniques can use specific wavelengths of light (e.g., ultraviolet (UV), visible light, or infrared (IR)) to image the underlying structure to which the overlying layer is to be aligned. However, in the fabrication of some structures, intervening opaque layers may be present. Optically opaque materials, such as those found in semi-damascene process flows or after processing magnetic tunnel junctions (MTJs) in magnetic random-access memory (MRAM), may exist between target structures, presenting specific challenges for alignment and overlay control. For example, the presence of intervening opaque materials generally requires additional patterning operations for measurement, significantly increasing process costs.

[0005] Other processing steps may create other types of underlying structures, including desired or undesirable structures. For example, some processing steps may create inclusions or voids within or between layers. Detecting the presence of underlying structures during the manufacturing process may be desirable.

[0006] Microscopy techniques that utilize non-optical methods for detecting or measuring structures buried beneath one or more layers, including desired structures (such as aligned or overlay structures) or undesired structures (such as inclusions or voids), are therefore desirable. Summary of the Invention

[0007] A time-resolved reflectivity metrology apparatus can be used to image underlying structures using a pulsed pump beam and a pulsed probe beam with varying time delays between the pulses. One or both of the beams are modulated. A camera having a multi-pixel array and independent phase locking for each pixel in the multi-pixel array receives and demodulates the reflected probe beam to produce an image. The camera records changes in reflectivity or surface deformation of the target sample at each pixel based on at least one time delay between the pump pulse and the probe pulse, thereby characterizing at least one property of the target sample.

[0008] In one embodiment, a metrology device for non-destructive metrology of a sample includes a light source for generating pulsed light; a pump arm; and a detector arm. The pump arm is configured to receive at least a first portion of the pulsed light and irradiate the sample with a pump beam having at least one pump pulse to induce a transient perturbation in the sample material, and the detector arm is configured to receive at least a second portion of the pulsed light and irradiate the sample with a probe beam having at least one probe pulse to generate a reflected probe beam modulated based on the transient perturbation in the sample material. At least one modulator modulates the at least one pump pulse in the pump beam. The metrology device includes a camera configured to receive and demodulate the reflected probe beam to generate an image of the sample, wherein each image varies with at least one time delay between the at least one pump pulse and the at least one probe pulse. The camera is configured to acquire transient signals from the image of the sample in parallel using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array to generate the image. The camera records a change in reflectivity or surface deformation of the sample at each pixel based on the at least one time delay between the at least one pump pulse and the at least one detection pulse. At least one processor is coupled to the camera and configured to measure at least one property of the sample based on a recorded reflectivity or surface deformation of the sample at each pixel based on the time delay between the at least one pump pulse and the at least one detection pulse.

[0009] In one embodiment, a method for non-destructive metrology of a sample includes generating pulsed light; irradiating the sample with a pump beam generated using at least a first portion of the pulsed light, the pump beam having at least one pump pulse to cause a transient perturbation in the sample material; and irradiating the sample with a probe beam generated using at least a second portion of the pulsed light to generate a reflected probe beam having at least one probe pulse, the reflected probe beam being modulated based on the transient perturbation in the sample material. At least the pump pulse in the pump beam is modulated. The method includes receiving and demodulating the reflected probe beam with a camera to generate an image of the sample, wherein each image varies with at least one time delay between the at least one pump pulse and the at least one probe pulse. The camera is configured to acquire transient signals from the image of the sample in parallel using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array to generate the image. The camera records a change in reflectivity or surface deformation of the sample at each pixel based on the at least one time delay between the at least one pump pulse and the at least one probe pulse. The method includes measuring at least one property of the sample based on a recorded reflectivity or surface deformation of the sample at each pixel based on the time delay between the at least one pump pulse and the at least one probe pulse. Simple diagram description

[0010] [ FIG1 ] shows a block diagram of a time-resolved reflectivity measurement apparatus using a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array. [ FIG. 2 ] shows another schematic diagram of a time-resolved reflectivity measurement apparatus using a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array. [FIG. 3] A schematic diagram of a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array. [ FIG. 4A ] illustrates the measurement of an embedded structure in the form of a metal structure in a sample using a multi-pixel array and parallel acquisition of transient signals with independent phase locking for each pixel in the multi-pixel array. [ FIG. 4B ] illustrates measurement of a buried structure in the form of a void in a sample using a multi-pixel array and parallel acquisition of transient signals with independent phase locking for each pixel in the multi-pixel array. [FIG. 5] is a flow chart illustrating a procedure for non-destructive time-resolved reflectivity measurement of a target on a sample using a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array. Implementation Method

[0011] The fabrication of semiconductor and similar devices requires a series of processing steps in which layers such as insulating layers, polysilicon layers, and metal layers are deposited and patterned. For proper operation of such devices, accurate overlay and alignment of successive layers are sometimes critical. During the fabrication process, non-destructive metrology techniques are used to ensure proper alignment and overlay using specially designed targets.

[0012] The target used for alignment and overlay consists of structures assigned to each layer (e.g., a bottom layer and a top layer). The target can be imaged, and the relative position of the top structure relative to the bottom structure can be determined from the image. The relative position of the top and bottom structures provides an indication of the alignment or overlay of their respective layers. To image the target in a conventional manner, light of a wavelength that can penetrate the sample to the bottom layer is used. For example, depending on the material composition of the top layer and any intervening layers between the top and bottom structures, different wavelengths of light (such as UV, visible light, or IR) can be used to resolve the bottom layer in the image.

[0013] The presence of opaque materials presents challenges for alignment and overlay. These materials, such as metal layers, can be found during semi-damascene process flows or after processing the magnetic tunneling junction (MTJ) of magnetic random access memory (MRAM) or other such devices. The presence of an intervening opaque layer between the top and bottom structures of a target prevents light from reaching the underlying structures, causing alignment or overlay measurement failures.

[0014] Furthermore, other types of buried structures may be created during the manufacturing process, including desired structures (such as lines and vias) and undesirable structures (such as inclusions or voids). For example, in advanced packaging processes, wafers may be bonded together, and voids may form between the bonded layers, such as beneath one or more layers. The presence of voids can affect the final performance of the device, and therefore, detecting their presence is desirable. For example, in some cases, it may be advisable to reprocess the bonded wafers before performing additional processing (such as polishing). The presence of one or more overlying layers (some of which may be opaque) can reduce the amount of light or block it from reaching the buried structures, thereby hindering the detection of the presence of undesirable structures. Currently, confocal scanning acoustic microscopy (C-SAM) is sometimes used to detect voids. Unfortunately, in order to properly transmit the acoustic signal using C-SAM technology, the sample must be immersed in water, which is often undesirable. Furthermore, the C-Sam technique is unable to image relatively small voids (e.g., below 10 µm in size) and is therefore limited in its usefulness.

[0015] Laser-induced time-resolved measurements include measurements of sample reflectivity and deflection, for example, resulting from one or more of the photoacoustic effect, the thermal background effect, the plasmonic effect, and any other physical phenomenon that produces transient reflectivity or deflection effects in response to light or other radiation. Time-resolved reflectivity measurements may sometimes be referred to herein as photoacoustic measurements or acoustic signal measurements, but unless otherwise stated, reference to acoustics is not intended to limit measurements of the photoacoustic effect and may additionally or alternatively include measurements of transient signals resulting from one or more other physical effects, such as the thermal background effect or the plasmonic effect. Examples of time-resolved reflectivity measurements include laser-induced transient signal measurements, such as picosecond laser acoustics (PLA), which can be used for measurements of buried structures (e.g., structures beneath one or more layers), for example, for measurements of alignment or overlay targets that include one or more intervening opaque layers between top and bottom structures of the target, or for detection or measurement of undesirable voids or inclusions. If the buried structure is located beneath one or more opaque layers, photoacoustic measurements can be particularly advantageous because they do not rely on light to penetrate the opaque layers, but instead generate and detect acoustic waves that propagate through the opaque layers. For example, time-resolved reflectivity metrology devices such as PLA can use ultrafast lasers (~100 fs pulse width), which allow for resolution of several fs.

[0016] In operation, conventional time-resolved reflectivity metrology devices can use localized raster scanning to map the approximate area of ​​an underlying structure. For time-resolved reflectivity measurements, the approximate time delay plane containing relevant image information to determine the structure's location can be limited to, for example, a time scan definition of less than 50 ps, ​​based on knowledge of device parameters such as layout and film stack information (including approximate layer materials and thicknesses). The time delay spans for multiple measurement locations, raw acoustic data, its Fourier transform, or thermal background, or a combination thereof, can be used alone or in conjunction with a principal component analysis (PCA) algorithm to form an image of the structure from which the location of the underlying structure can be derived. Additionally or alternatively, non-PCA analysis can be used to identify local regions in frequency space that capture signal differences between regions above and outside the underlying structure and to find highly correlated local regions in time space.

[0017] The use of raster scanning (or other similar types of scanning) requires movement of the sample and / or metrology head in the X and Y (or R-θ) directions, with each site measured separately to obtain a two-dimensional (2D) image of the underlying structure. The throughput of the mapping method is governed by the number of sites in the scan, as well as the range, resolution, and number of sweeps collected at each site. In some cases, generating a 2D image of the underlying structure using raster scanning with time-resolved reflectivity measurements can take up to several minutes or hours. To incorporate the use of time-resolved reflectivity measurements for 2D imaging in a high-volume manufacturing (HVM) environment, the total imaging time should be on the order of seconds.

[0018] As discussed herein, time-resolved reflectivity measurements, including picosecond laser acoustic (PLA) measurements, can utilize a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array. A pump arm in the time-resolved reflectivity measurement apparatus is configured to irradiate a target sample with at least one pump pulse to induce a transient perturbation in the target material, and a probe arm is configured to irradiate the target sample with at least one probe pulse to generate a reflected probe pulse modulated based on the transient perturbation in the target material. One or more modulators can be used to modulate (e.g., frequency modulate) the pump pulse, the probe pulse, or both. A camera having a multi-pixel array and independent phase locking for each pixel in the multi-pixel array receives and demodulates the reflected probe pulses to generate images of the sample, each image varying with a different time delay between the pump pulse and the probe pulse. For example, a camera can record changes in the reflectivity or surface deformation of a target sample at each pixel based on the time delay between a pump pulse and a probe pulse. At least one property of the target sample can be characterized, such as overlay, alignment, or the presence of undesirable structures (such as inclusions or voids). The focused pump and probe beams can cover a region of the target sample that includes the structure to be imaged. For example, the focal regions of the pump and probe beams can be adjusted to approximately tens of micrometers to encompass the structure to be imaged. Thus, structures with dimensions equivalent to the focal regions of the pump and probe beams can be imaged without scanning, significantly reducing the total imaging time to, for example, seconds, compared to minutes or hours required using scanning. Furthermore, underlying structures can be imaged in three dimensions based on multiple images generated with varying time delays between the pump and probe pulses.

[0019] FIG1 illustrates a block diagram of an example time-resolved reflectivity metrology device 100, which can utilize a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array, as discussed herein. Typically, device 100 includes a pump laser 120 (also referred to herein as an excitation laser), a probe laser 122 (also referred to herein as a detection laser), and optical components such as a steering mirror 123 and a beamsplitter 121, as well as lenses 136 and 138, filters, polarizers, and the like (not shown) that direct radiation from the pump laser 120 and the probe laser 122 over a region of substrate 112 that includes the structure 110 to be imaged. The device can further include a modulator 124 (e.g., such as an electro-optical module (EOM)) that modulates the pump pulses in the pump arm at a modulation frequency, and in some embodiments, a second modulator 124′ that modulates the probe pulses in the detection arm at a different modulation frequency. The apparatus 100 may include optical components, such as a beamsplitter 125 and a turning mirror 127, and may include a beam stack 126 for capturing radiation from the pump laser returning from the structure 110. The apparatus 100 includes a camera 128, which includes a multi-pixel array 132 and independent phase locking for each of the multi-pixel arrays, and is configured to record changes in the reflectivity or surface deformation of the substrate 112 at each pixel based on the time delay between the pump pulse and the probe pulse. The apparatus 100 further includes an electromechanical support 129 for the substrate 112 of which the structure 110 is a part, the electromechanical support 129 being adapted to move the substrate 112 relative to the pump laser 120 and the probe laser 122 to obtain measurements from a desired location. The apparatus further includes a processing system 130 coupled to the probe and pump lasers 122, 120, the electromechanical support 129, and the camera 128.

[0020] It should be understood that the processing system 130 may be a self-contained or distributed computing device capable of performing calculations, receiving and sending instructions or commands, and receiving, storing, and sending information related to the metering functions of the device.

[0021] In the depicted embodiment, the pump laser 120 and the probe laser 122 of the embodiment of the time-resolved reflectivity metrology apparatus 100 shown in FIG1 can share at least a portion of the optical path to and from the structure 110. For example, the lasers can have a number of different relative configurations, including configurations in which the paths are identical, partially overlapping, adjacent, or coaxial. In some embodiments, the pump beam and the probe beam can be derived from the same pulsed laser. In some embodiments, separate lasers can be used for the pump beam and the probe beam, for example, separate lasers with slightly different repetition rates can be used in an asynchronous optical sampling (ASOPS) configuration. In other embodiments, the pump laser 120 and the probe laser 122, as well as the beam stack 126 and the camera 128, do not share an optical path. For example, the pump beam from the pump laser 120 can be incident normally on the substrate 112, while the probe beam from the probe laser 122 can be incident obliquely on the substrate 112. The pump laser 120 and the probe laser 122 can be directly controlled to obtain the temporal spacing between the light pulses directed to the structure 110 .

[0022] It should be understood that many optical configurations are possible. In some configurations, the pump may be a pulsed laser with a pulse width ranging from hundreds of femtoseconds to hundreds of nanoseconds, and the probe beam is coupled to a beam deflection system. For example, in a system where the probe is also pulsed, the device may employ a delay stage (not shown) to increase or decrease the optical path length between the laser and the structure 110 associated therewith. If a delay stage is provided, it will be controlled by the processing system 130 to obtain and control the time delay between the pump light pulse and the probe light pulse incident on the object. Many other alternative configurations are also possible. In other embodiments (such as those with an ASOPS configuration), the device may not include a delay stage. It should be understood that the schematic diagram of FIG. 1 is not intended to be limiting, but rather depicts one of several example configurations for the purpose of explaining the novel features of the present disclosure.

[0023] In operation, the time-resolved reflectivity metrology apparatus 100 directs a series of light pulses from a pump laser 120 toward the structure 110. These light pulses are incident (i.e., at any angle between zero and 90 degrees, including, for example, 45 and 90 degrees) on the transducer layer in the structure 110 and are at least partially absorbed by the transducer layer. The absorption of light by the transducer layer causes a transient expansion in the material of the structure 110. The expansion is short enough that it induces ultrasonic waves that propagate substantially vertically through the structure 110 and are reflected at underlying interfaces in the film stack and returned to the top surface. Light from the pump laser 120 that reflects from the structure 110 is transferred to the beam stack 126, which dissipates or absorbs the pump radiation.

[0024] In addition to directing the operation of pump laser 120, processing system 130 directs the operation of probe laser 122. Probe laser 122 directs radiation in a series of light pulses incident on structure 110 that is reflected from the top layer of structure 110 and is affected by the reflected ultrasonic waves that return to the top surface of structure 110.

[0025] 1 shows a modulator 124 for modulating the pump pulse from the pump laser 120 and a modulator 124′ for additionally modulating the probe pulse from the probe laser 122. For example, modulators 124 and 124′ may be EOMs and may modulate the frequency of the pump pulse or both the pump pulse and the probe pulse (e.g., using two frequency combs).

[0026] Apparatus 100 includes optical devices, such as lens 136, that can be configured to adjust the spot size of the pump and probe beams based on the specific target being measured. The spot sizes of the respective beams can be similar or dissimilar. For example, optical devices, such as lens 136, can be configured to adjust the focal region of the pump and probe pulses on substrate 112 to at least the size of the structure 110 being measured, allowing structure 110 to be measured without scanning. For example, the diameter of the focal region on substrate 112 can be greater than 20 µm. The spot size of the pump and probe beams can be based in part on the size of the structure being measured or on a balance between signal strength and thermal budget for the structure being measured.

[0027] Light reflected from the surface of structure 110 is directed from structure 110 via, for example, beam splitter 125, and the probe beam is imaged by camera 128. For example, the reflectivity of the reflected light at the top surface may change due to changes in reflectivity or surface deformation caused by reflected ultrasound waves returning from the top surface. In the presence of a transparent layer, the reflected light may constructively and destructively interfere with the propagating ultrasound waves, generating interference oscillations. Camera 128 may be configured to receive and demodulate the reflected probe pulses to produce an image of substrate 112, thereby sensing intensity changes in the optical probe beam caused by changes in reflectivity and / or interference oscillations.

[0028] Camera 128 includes a multi-pixel array 132 that receives a probe beam. Optics, such as a lens 138, can adjust the magnification of the probe beam on multi-pixel array 132 for efficiency. Camera 128 can include parallel phase locking circuitry 134 configured to independently phase lock each pixel in the multi-pixel array for parallel acquisition of transient signals (such as acoustic signals or thermal background signals) to generate an image of substrate 112. In certain embodiments, parallel phase locking circuitry 134 can be independent of camera 128 (e.g., in a separate processor or field programmable gate array (FPGA)). Independent phase locking of each pixel in multi-pixel array 132 can be used to demodulate the frequency of pump pulses in a received probe beam. If both pump pulses and probe pulses are modulated by modulators 124 and 124', respectively, the combination (e.g., sum or difference) of the frequencies in the received probe beam can be demodulated. Camera 128 can record changes in the reflectivity or surface deformation of substrate 112 at each illuminated pixel of multi-pixel array 132 based on the time delay between the pump pulse and the probe pulse. For example, camera 128 can generate multiple images of substrate 112, each image generated with a different time delay between the pump pulse and the probe pulse. For example, camera 128 can be configured to generate in-phase measurements and 90-degree out-of-phase measurements.

[0029] The pump pulse and the probe pulse can be generated at different delays, and the camera 128 can generate images of the sample, where each image is generated with a different time delay between the pump pulse and the probe pulse. For example, each image generated by the camera 128 can correspond to the arrival of a transient signal (such as an acoustic echo or thermal background) from the underlying layer at a different depth within the patterned structure, thereby enabling the detection of desired and undesired structures in the underlying layer.

[0030] Furthermore, the time-resolved reflectivity metrology device 100 can be coupled to an imaging device 140 configured to image the top structure of the film stack (e.g., for alignment or overlay purposes). For example, the imaging device 140 can be a channel camera. The imaging device 140 can perform optical imaging of the structure 110. However, due to one or more opaque layers in the structure 110, the optical image of the structure 110 produced by the imaging device 140 may only include the top structure.

[0031] When the focused probe beam covers an area of ​​substrate 112 including underlying structure 110 with a surrounding background, camera 128 generates an image with a specific time delay corresponding to the arrival of transient signals from the structure, which is a representative image of the underlying structure 110. The focal regions of the pump and probe beams generated by optical devices (such as lens 136) can be adjusted to approximately tens of micrometers. Thus, structures with dimensions equivalent to the beam focal region can be imaged without the need for raster scanning, significantly reducing the total imaging time from minutes or hours for raster scanning to, for example, seconds. Furthermore, structures significantly smaller than the beam focal region (e.g., structures smaller than a pixel or smaller than 10 µm) can be detected.

[0032] Figure 2 shows a schematic diagram of an example time-resolved reflectivity metrology device 200, which can utilize a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array, as discussed herein. As shown, light can be generated by a light source 202, such as a 520 nm, 200 fs, 60 MHz laser. However, other light source characteristics can be used, including light sources operating in the infrared wavelength range, for example, for imaging embedded structures. The light is directed through an intensity control 203, which can include a half-wave plate HWP1 and a polarizer P1, and can be directed through a beam expander 204. The beam can be directed by a mirror M1 to a pump-probe separator 206, which can include a polarization beam splitter.

[0033] In pump arm 220, the pump beam is directed by mirror M2 to variable delay 222, which includes mirrors M3, M4, and M5. Mirror M4 moves to adjust the delay in the pump beam. For example, mirror M4 can be a retroreflector or mirror coupled to an actuator or voice coil with a physical displacement of, for example, approximately 25 mm or 83.3 ps, for achieving short and repeatable pump pulse time delays. The pump beam passes through modulator 226 (e.g., an electro-optical modulator (EOM)), followed by polarizer P2 and half-wave plate HWP2, which can be motorized for rotation. The pump beam is directed by beam deflecting mirrors (e.g., mirrors M6, M7, and M8) to focusing unit 240. At least one of mirrors M6, M7, and M8 can be attached to a piezoelectric motor to adjust the direction of the pump beam. 2 , focusing unit 240 may include a beam splitter 242 that directs the pump beam through lens L1 to be incident normally on sample 201. Lens L1 focuses the pump beam over a region of sample 201 that includes the structure to be imaged. In certain embodiments, the pump beam may be directed to be incident obliquely on sample 201 (e.g., along the same beam path as the probe beam).

[0034] In the probe arm 230, after the pump-probe separator 206, the probe beam can pass through a half-wave plate HWP2, which can be motorized for rotation. The probe beam can be directed to a probe delay 232, which includes mirrors M9, M10, M11, and M12. For example, mirror M11 can be a retroreflector and coupled to an actuator or voice coil to adjust the delay of the probe beam. The probe beam is directed to a focusing unit 240 by beam deflection mirrors (e.g., mirrors M13, M7, and M14). At least one of the mirrors M13, M7, and M14 can be attached to a piezoelectric motor to adjust the direction of the probe beam. As shown in FIG2 , the focusing unit 240 can direct the probe beam through a lens L2 for oblique incidence on the sample 201. Lens L2 focuses the probe beam over a region of the sample 201 that includes the structure to be imaged and coincides with the incident region of the pump beam. In certain implementations, similar to the pump beam, the probe beam can pass through a modulator (e.g., an EOM) and then through a polarizer and a half-wave plate that can be powered to rotate to modulate the frequency of the probe beam (e.g., using a different frequency comb than the pump beam).

[0035] For example, lenses L1 and L2 can be configured to produce coincident points on sample 201 that are at least the size of the structure being measured on sample 201, so that scanning is not required to image the desired structure (such as an alignment or overlay pattern). For example, in some embodiments, lenses L1 and L2 can have a focal area greater than 20 μm.

[0036] Variable delay 222 and probe delay 232 can operate in absolute or relative (with fixed amplitude and sinusoidal waveform) displacement modes. For example, due to local topography and film thickness variations, localization in the time delay can be detrimental, hindering faster scanning. Data can be collected at a fixed position on the voice coil using a fixed-amplitude (1.5 mm) sinusoidal oscillation at the frequency of the retro-reflector M14 (10 kHz), yielding a delay of + / - 5 ps. Using a time constant optimized for the sinusoidal oscillation on the lock-in amplifier, the voltage output can then be the average of reflectivity variations over the selected time delay range, alleviating operational concerns associated with fixed positions.

[0037] The reflected probe beam (and optionally the reflected pump beam, if incident at an oblique angle) is received by collection optics 250, which includes, for example, lens L3 and mirrors M15 and M16. The reflected beam is directed to a detection unit 260, which includes a camera 262 having a multi-pixel array 263. In certain embodiments, detection unit 260 may additionally include a flip mirror 266 or a beam splitter, which can be used to selectively direct the reflected beam to a detector 268. For example, the reflected beam can be received by camera 262 via a relay lens 264 and imaged onto multi-pixel array 263. Optics (e.g., relay lens 264) can adjust the magnification of the probe beam on multi-pixel array 263 to improve efficiency. Camera 262 is configured for independent phase locking of each pixel in multi-pixel array 263 for parallel acquisition of transient signals (such as acoustic signals or thermal background signals) from the image of sample 201. Independent phase locking for each pixel in multi-pixel array 263 can be used to demodulate the received probe beam based on the frequency of the pump pulses generated by modulator 226 (and the modulator in detection arm 230, if present), or a combination of the frequencies of the pump pulses and the detection pulses. In embodiments where both the pump pulses in the pump beam and the detection pulses in the detection beam are modulated with two different frequency combs (e.g., by modulators in both pump arm 220 and detection arm 230), independent phase locking for each pixel in multi-pixel array 263 can be used to demodulate the frequency combination (e.g., sum or difference). Furthermore, independent phase locking for each pixel in multi-pixel array 263 can generate both in-phase and ninety-degree phase difference measurements from the image. Camera 262 can record changes in the reflectivity or surface deformation of sample 201 at each illuminated pixel in multi-pixel array 263 based on the time delay between the pump pulses and the detection pulses.

[0038] The pump pulse and the probe pulse can be generated with different time delays, and camera 262 can generate multiple images with different time delays. Each image generated by camera 262 corresponds to the arrival of a transient signal (e.g., acoustic echo or thermal background) from an underlying layer within the patterned structure, and the different time delays between the pump pulse and the probe pulse correspond to different depths in the underlying layer. Therefore, by generating multiple images with different time delays between the pump pulse and the probe pulse, buried structures at different depths in the underlying layer can be detected.

[0039] Furthermore, the time-resolved reflectivity measurement device 200 may be coupled to an imaging device 244, which may be configured to image the top structure of the sample 201 via a beam splitter 242 and a lens L1. For example, the imaging device 244 may be a channel camera.

[0040] Sample 201 is held on a stage 205, which includes or is coupled to one or more actuators configured to move sample 201 relative to the optical system of time-resolved reflectivity metrology apparatus 200 so that various locations on sample 201 can be measured. In the depicted embodiment, the apparatus may include additional components and subsystems, such as beam management and conditioning components (e.g., beam expanders, collimators, polarizers, half-wave plates, etc.), as well as beam power detectors and height detectors. Those skilled in the art will appreciate that variations of the apparatus depicted in Figures 1 and 2 will still be suitable for practicing the time-resolved reflectivity metrology techniques described herein.

[0041] The camera 262 and other components of the time-resolved reflectivity metrology device 200 (such as the detector 268, the light source 202, the variable delay 222, and the stage 205 on which the sample 201 is held) can be coupled to a processing system 270 (such as a workstation, a personal computer, a central processing unit, or other suitable computer system or systems). It should be understood that a single processor, multiple separate processors, or multiple coupled processors can be used, all of which are interchangeably referred to herein as the processing system 270. The processing system 270 is preferably included in, connected to, or otherwise associated with the time-resolved reflectivity metrology device 200. For example, the processing system 270 can control the positioning of the sample 201 by controlling the movement of the stage 205 on which the sample 201 is held. For example, the stage 205 can be capable of horizontal movement in either Cartesian (i.e., X and Y) coordinates or polar (i.e., R and θ) coordinates, or some combination of both. Stage 205 may also be capable of vertical movement along the Z coordinate. Processing system 270 may further control the operation of a chuck on stage 205 used to hold or release sample 201. Processing system 270 may also collect and analyze data from camera 262, detector 268, and imaging device 244. Processing system 270 may analyze time-resolved reflectivity metrology data to determine the location of structures in sample 201 that may be beneath one or more opaque layers. Processing system 270 may further analyze imaging data to determine the location of structures above the target, thereby determining the relative position of the structures above with respect to the underlying structures, and thus determining alignment or overlay. For example, in certain embodiments, the underlying structure may be imaged in three dimensions based on multiple images generated with different time delays between the pump pulse and the probe pulse. Processing system 270 may use the measured data for localized mapping of buried structures (e.g., using one or more images acquired by camera 262). For example, if the spot sizes of the pump and probe beams overlap the buried structure being measured (such as an overlay target), only a single image may be used. However, if the structure is larger than the dot size, or if the dot is not properly aligned with the structure, multiple images can be acquired by camera 262 and stitched together. If the buried structure is relatively small (e.g., the size of a pixel or sub-pixel of camera 262), such as a void or inclusion, multiple structures can be measured or detected simultaneously over a large area of ​​the sample using camera 262. The location of the underlying structure can be derived using raw time-resolved reflectivity data from one or more images of the structure, or processed data (such as its Fourier transform), or thermal background, or a combination thereof. In certain embodiments, a principal component analysis (PCA) procedure can be used with the data from one or more images of the structure. Additionally or alternatively, non-PCA analyses can be used to identify local regions in frequency space that capture signal differences between areas above and outside the underlying structure, and to find highly correlated local regions in time space.The processing system 270 may alternatively or additionally process time-resolved reflectivity measurement data for edge detection or triangulation (e.g., using a classification library or neural network generated by the time-resolved reflectivity measurement device 200 (or another device) on a reference sample). For example, a classification library may be established based on time-resolved reflectivity measurement data collected from locations above and outside a substructure of a reference target. The classification library (or neural network) may be used in conjunction with one or more time-resolved reflectivity measurements at locations in the vicinity of the substructure to determine whether each location is above or outside the substructure. Additional time-resolved reflectivity measurements may be acquired at new locations and compared to the classification library as dictated by a predefined search pattern or algorithm until one or more edges of the substructure are located, thereby determining the location of the substructure.

[0042] Processing system 270 includes at least one processor 272 with memory 274 and a user interface including, for example, a display 276 and an input device 278. A non-transitory computer-usable storage medium 279 having embodied computer-readable program code can be used by processing system 270 to control time-resolved reflectivity measurement device 200 and perform functions, including the analysis described herein. Data structures, libraries, and software code for automatically implementing one or more of the actions described in this embodiment can be implemented by one of ordinary skill in the art according to the present disclosure and stored, for example, on computer-usable storage medium 279. The computer-usable storage medium can be any device or medium capable of storing code and / or data for use by a computer system (such as at least one processor 272). Computer-usable storage medium 279 can include, but is not limited to, flash drives, magnetic and optical storage devices such as disk drives, tapes, optical discs, and DVDs (digital versatile discs or digital video discs). Communication port 277 can also be used to receive instructions for programming processing system 270 to perform any one or more of the functions described herein and can represent any type of communication connection, such as to the Internet or any other computer network. Communication port 277 can further export signals (e.g., having alignment or overlay measurement results and / or instructions) to another system (such as an external processing tool) in a feedforward or feedback process to adjust process parameters associated with a sample manufacturing process step based on the measurement results. Additionally, the functions described herein can be embodied in whole or in part within the circuitry of an application specific integrated circuit (ASIC) or programmable logic device (PLD), and the functions can be embodied in a computer-understandable descriptor language that can be used to create an ASIC or PLD that operates as described herein. Results from the data analysis can be stored, for example, in memory 274 in association with the sample and / or provided to a user (e.g., via display 276, an alarm, or other output device). Furthermore, the results from the analysis can be fed back to the process equipment to adjust the appropriate patterning steps to compensate for any detected misalignment or overlay errors in the multi-patterning process.

[0043] FIG3 is a schematic diagram of a camera 300 configured for parallel acquisition of transient signals (such as acoustic signals or thermal background signals) using a multi-pixel array 310 and independent phase locking for each pixel in the multi-pixel array 310. For example, the camera 300 can be used as the camera 128 in FIG1 or the camera 262 in FIG2 and is configured for parallel acquisition of transient signals to generate an image of a sample.

[0044] For example, FIG3 shows a close-up of a single pixel 312 in a multi-pixel array 310, which is shown to include a photodiode 314 and associated phase-locking circuitry 320. Each pixel in the multi-pixel array 310 can be associated with a separate phase-locking circuit. The phase-locking circuitry can be part of the camera 300 or can be separate from the camera (e.g., in a separate processor or FPGA).

[0045] As shown, phase-locking circuit 320 associated with photodiode 314 (for pixel 312 in multi-pixel array 310) can be configured to generate both an in-phase measurement and a 90-degree phase difference measurement. For example, the signal from photodiode 314 is multiplied by a modulation frequency at multiplier 322 and then filtered by low-pass filter 324 to generate the in-phase measurement. For example, the modulation frequency can be provided by a local oscillator and applied to the pump beam, the probe beam, or both. Additionally, the signal from photodiode 314 can be multiplied by a modulation frequency (e.g., from a local oscillator) shifted 90° by shifter 327 at multiplier 326 and then filtered by low-pass filter 328 to generate the 90-degree phase difference measurement.

[0046] In operation, the pump pulse is modulated, or the pump pulse and probe pulse are modulated at different frequencies (e.g., using one or more modulators (e.g., modulators 124, 124', 226 in Figures 1 and 2)). Camera 300 receives the reflected probe pulse using a multi-pixel array 310, which is modulated based on the modulation of the pump pulse or based on a combination of the pump pulse and the probe pulse, and independently demodulates each pixel to produce an image of the sample, where each image varies with a different time delay between the pump pulse and the probe pulse. For example, if both the pump pulse and the probe pulse are modulated, the received probe beam is demodulated based on a combination (e.g., the sum or difference) of the modulation frequencies of the pump and probe beams. Camera 300 can record, at each pixel of the image, a change in the reflectivity or surface deformation of the sample, which can be characterized by the time delay between the pump and probe pulses.

[0047] By way of example, FIG4A illustrates a sample measurement using parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array, as discussed herein. For example, FIG4A illustrates a sample 400 including a buried tungsten (W) structure 410. For example, sample 400 includes a substrate 402 having a silicon oxide (SiO2) layer 404, a silicon carbon nitride (SiCN) layer 406, a SiO2 layer 408 having the W structure 410 buried by a tantalum nitride (TaN) layer 412, a magnetic tunneling junction (MTJ) layer 414, a titanium nitride (TiN) layer 416, and a SiO2 layer 418. It should be understood that sample 400 is merely an example, and other types of samples may be measured, including samples having additional or fewer layers and samples having different types of layers or structures. As shown, pump beam 420 may be incident normally on surface 401 of sample 400, and probe beam 430 may be incident obliquely and reflected off surface 401 of sample 400. Furthermore, as shown, at a single point 440 (e.g., corresponding to a single pixel of a camera (such as camera 300 shown in FIG3 )), transient signals in the form of acoustic reflections occur at several different interfaces, which can be detected by camera 300 at different times. For example, at time t1, a transient signal from surface 401 may be detected, while at times t2, t3, and t4, transient signals from the interfaces between layers 416 and 414, layers 414 and 412, and layer 412 and W structure 410, respectively, may be detected. It should be understood that although FIG. 4A illustrates the transient signal received at a single point 440, the pump beam 420 and the probe beam 430 are incident upon an area of ​​comparable size to the W structure 410, and therefore, the transient signal is similarly received over the entire area of ​​the incident beam, which can be acquired in parallel by the multi-pixel array of the camera.

[0048] By way of example, FIG4B illustrates another example of sample measurement using parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array, as discussed herein. For example, FIG4B illustrates sample 450 comprising two bonded wafers 460 and 470, with buried voids 482 and 484 disposed between the bonded wafers. For example, wafer 460 comprises a silicon substrate 462, a silicon nitride (SiN) layer 464, a silicon oxide (SiO2) layer 466, a SiN layer 468, and a copper (Cu) bonding pad 469. Wafer 470 is similar to wafer 460, but inverted, and comprises a silicon substrate 472, a SiN layer 474, a SiO2 layer 476, a SiN layer 478, and a Cu bonding pad 479. As illustrated, voids 482 and 484 are disposed between SiN layers 468 and 478. It should be understood that sample 450 is merely an example, and other types of samples can be measured, including samples with additional or fewer layers and samples with different types of layers or structures. As discussed in FIG4A , pump beam 420 can be incident normally on surface 451 of sample 450, and probe beam 430 can be incident obliquely and reflected off surface 451 of sample 450. Furthermore, as illustrated, at a single point 490 (e.g., corresponding to a single pixel of a camera (such as camera 300 shown in FIG3 )), transient signals in the form of acoustic reflections or thermal background signals occur at several different interfaces, which can be detected by camera 300 at different times. For example, at time t1, a transient signal can be detected from surface 401, while at times t2, t3, and t4, transient signals can be detected from the interfaces between layers 474 and 476, layers 476 and 478, and layer 478 and void 482, respectively. It should be understood that although FIG4B illustrates the transient signal received at a single point 490, the pump beam 420 and the probe beam 430 are incident upon an area including multiple voids, as illustrated by voids 482 and 484, and transient signals are similarly received over the entire area of ​​the incident beams, which can be acquired in parallel by the multi-pixel array of the camera, thereby enabling the simultaneous detection of the presence of both voids 482 and 484.

[0049] FIG5 is a flow chart 500 illustrating a process for non-destructive time-resolved reflectivity measurement of a target on a sample using a camera configured for parallel acquisition of transient signals using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array, as discussed herein. For example, the process can be performed using the time-resolved reflectivity measurement devices 100 or 200 shown in FIG1 and 2, respectively, or the camera 300 shown in FIG3.

[0050] As shown, at block 502 , the process includes generating pulsed light, such as discussed with reference to the pump laser 120 and the probe laser 122 shown in FIG. 1 and the light source 202 shown in FIG. 2 .

[0051] At block 504, the process includes irradiating the sample with a pump beam generated using at least a first portion of pulsed light, the pump beam having at least one pump pulse to cause transient perturbations in the sample material, such as discussed with reference to the pump laser 120 shown in FIG. 1 and the pump arm 220 shown in FIG. 2 .

[0052] At block 506, the process includes irradiating the sample with a probe beam generated using at least a second portion of the pulsed light to generate a reflected probe beam, the probe beam having at least one probe pulse, the reflected probe beam modulated based on a transient perturbation in the sample material, e.g., as discussed with reference to the probe laser 122 shown in FIG. 1 and the probe arm 230 shown in FIG. 2 .

[0053] At block 508, the process includes modulating at least one pump pulse in at least the pump beam, e.g., as discussed with reference to the modulators 124, 124' shown in FIG1 and the modulator 226 shown in FIG2. In some embodiments, the process includes modulating at least one pump pulse in the pump beam and at least one probe pulse in the probe arm, e.g., as discussed with reference to the modulators 124, 124' shown in FIG1 and the modulator 226 shown in FIG2.

[0054] At block 510, the process includes receiving and demodulating the reflected probe beam with a camera to generate images of the sample, wherein each image varies with at least one time delay between at least one pump pulse and at least one probe pulse, the camera being configured to acquire transient signals from the images of the sample in parallel using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array to generate the images, wherein the camera records a change in reflectivity or surface deformation of the sample at each pixel as a function of the at least one time delay between the at least one pump pulse and the at least one probe pulse, for example, as discussed with reference to cameras 128, 262, and 300 shown in FIG. 1 , FIG. 2 , and FIG. 3 , respectively.

[0055] At block 512, the process includes measuring at least one property of the sample based on the recorded reflectivity or surface deformation of the sample at each pixel according to at least one time delay between at least one pump pulse and at least one probe pulse, for example, as discussed with reference to processing systems 130 and 270 shown in FIG. 1 and FIG. 2 , respectively. For example, in some embodiments, the at least one property of the sample may be at least one of alignment, overlay, and presence of voids. In some embodiments, the at least one property of the sample may include a property of an underlying structure that is imaged in three dimensions based on an image generated by the at least one time delay between the at least one pump pulse and the at least one probe pulse.

[0056] In some embodiments, the process may include focusing the pump and probe beams on the sample in a focal region greater than 20 μm, e.g., as discussed with reference to lenses 136, L1, and L2 shown in Figures 1 and 2. For example, the focal region of the pump and probe beams on the sample may have a size at least as large as the size of the structure under test on the sample, e.g., as discussed with reference to lenses 136, L1, and L2 shown in Figures 1 and 2.

[0057] In some embodiments, the process may further include generating a plurality of images of the sample with a camera, wherein each image is generated with a different time delay between at least one pump pulse and at least one probe pulse, for example, as discussed with reference to cameras 128, 262, and 300 shown in Figures 1, 2, and 3, respectively.

[0058] In some embodiments, the probe beam may be incident on an area of ​​the sample covering a patterned structure, wherein each image of the sample produced by the camera corresponds to the arrival of an acoustic echo from an underlying layer within the patterned structure to detect buried structures in the underlying layer of the patterned structure, for example, as discussed with reference to Figures 1 and 2.

[0059] In some embodiments, modulating at least one pump pulse in at least the pump beam modulates the frequency of at least one pump pulse in the pump beam, and demodulating the frequency for independent phase locking of each pixel in a multi-pixel array, for example, as discussed with reference to modulator 124 shown in FIG. 1 and modulator 226 shown in FIG. 2 , and cameras 128 , 262 , and 300 shown in FIG. 1 , FIG. 2 , and FIG. 3 , respectively.

[0060] In some embodiments, modulating at least one pump pulse in at least the pump beam may include modulating a first frequency of at least one pump pulse in the pump beam with a first modulator and modulating a second frequency of at least one detection pulse with a second modulator, and demodulating the frequency based on a combination of the first frequency and the second frequency for independent phase locking of each pixel in the multi-pixel array, for example, as discussed with reference to the modulator 124 shown in Figure 1 and the modulator 226 shown in Figure 2, and the cameras 128, 262, and 300 shown in Figures 1, 2, and 3, respectively.

[0061] In some embodiments, the process further includes generating an in-phase measurement and a ninety degree phase difference measurement from an image of the sample received by a camera, such as discussed with reference to cameras 128, 262, and 300 shown in Figures 1, 2, and 3, respectively.

[0062] The above description is intended to be illustrative and non-limiting. For example, the above examples (or one or more aspects thereof) may be used in combination with one another. Other implementations may be used, such as by a person of ordinary skill in the art reviewing the above description. Furthermore, in the above implementations, various features may be combined to simplify the disclosure. The subject matter of the present invention may encompass less than all features of the specifically disclosed implementations. Therefore, the following aspects are hereby incorporated into the implementations as examples or implementations, each of which stands alone as a separate implementation, and it is contemplated that such implementations may be combined with one another in various combinations or permutations. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.

[0063] 100: Time-resolved reflectivity measurement device; device 110: Structure to be imaged; Structure; Underlying structure 112: Base material 120: Pump Laser 121: Optical Splitter 122: Detection Laser 123: Steering Mirror 124: Modulator 124': Second modulator 125:Spectrum Splitter 126: Bundle Stack 127: Steering Mirror 128: Camera 129: Electromechanical support parts 130:Processing System 132:Multi-pixel array 134: Parallel phase-locked circuit 136: Lens 138: Lens 140: Imaging device 200: Time-resolved reflectivity measurement device 201: Sample 202: Light Source 203: Intensity Control 204: Beam Expander 205:pedestal 206: Pump detection separator 220: Pump arm 222:Variable Delay 226: Modulator 230: Detection Arm 232: Detection delay 240: Focusing unit 242:Spectrum Splitter 244: Imaging device 250: Collection optics 260:Detection Unit 262: Camera 263:Multi-pixel array 264: Relay lens 266: Flip Mirror 268: Detector 270:Processing System 272: Processor 274:Memory 276: Display 277: Communication port 278: Input device 279: Non-transitory computer-usable storage media; computer-usable storage media 300: Camera 310: Multi-pixel array 312: single pixel; pixel 314: Photodiode 320: Phase-locked circuit 322: Multiplier 324: Low-pass filter 326: Multiplier 327:Shifter 328: Low-pass filter 400: Sample 401: Surface 402: base material 404: Silicon oxide (SiO 2) layer 406: Silicon Carbon Nitride (SiCN) layer 408:SiO 2 layer 410: buried tungsten (W) structure; W structure 412: Tantalum nitride (TaN) layer; layer 414: Magnetic tunneling junction (MTJ) layer; layer 416: Titanium nitride (TiN) layer; layer 418:SiO 2 layer 420: Pump beam 430: Probe beam 440: Single point 450: Sample 451: Surface 460: Wafer 462:Silicon substrate 464: Silicon nitride (SiN) layer 466: Silicon oxide (SiO 2) layer 468:SiN layer 469: Copper (Cu) bonding pad 470: Wafer 472:Silicon substrate 474: SiN layer; layer 476: SiO 2 layer; layer 478: SiN layer; layer 479:Cu bonding pad 482: buried gap; gap 484: buried gap; gap 490: Single point 500:Flowchart 502,504,506,508,510,512: Blocks HWP1: half wave plate HWP2: half wave plate L1, L2, L3: Lens M1:Mirror M2:Mirror M3:Mirror M4:Mirror M5:Mirror M6:Mirror M7:Mirror M8:Mirror M9:Mirror M10:Mirror M11:Mirror M12:Mirror M13:Mirror M14: Mirror; Retroreflector M15:Mirror M16:Mirror P1: Polarizer P2: Polarizer t1,t2,t3,t4: time

Claims

1. A metrological apparatus for nondestructive metrology of a sample, comprising: a light source for generating pulsed light; a pump arm configured to receive at least a first portion of the pulsed light and irradiate the sample with a pump beam having at least one pump pulse to cause a transient disturbance in the sample material; a probe arm configured to receive at least a second portion of the pulsed light and irradiate the sample with a probe beam having at least one probe pulse to generate a reflected probe beam, the reflected probe beam being modulated based on the transient disturbance in the sample material; and at least one modulator for modulating at least one pump pulse in the pump beam. A camera configured to receive and demodulate the reflected probe beam to generate an image of the sample, wherein each image varies with at least one time delay between the at least one pump pulse and the at least one probe pulse, the camera configured to acquire transient signals from the sample in parallel using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array to generate the image, the camera recording changes in reflectivity or surface deformation of the sample at each pixel based on the at least one time delay between the at least one pump pulse and the at least one probe pulse, wherein the at least one modulator includes a first modulator and A second modulator, the first modulator configured to modulate a first frequency of the at least one pump pulse in the pump bundle, the second modulator configured to modulate a second frequency of the at least one probe pulse in the probe arm, and wherein the frequency is demodulated based on a combination of the first and second frequencies for the independent phase locking of each pixel in the multi-pixel array; and at least one processor coupled to the camera and configured to measure at least one property of the sample based on the recorded reflectivity or surface deformation of the sample at each pixel according to at least one time delay between the at least one pump pulse and the at least one probe pulse.

2. The metering device of claim 1, wherein the at least one property of the sample includes the property of an underlying structure, the underlying structure being three-dimensionally imaged based on the image generated by the different time delay between the at least one pump pulse and the at least one probe pulse.

3. The measuring device of claim 1, wherein the at least one property of the sample includes at least one of alignment, overlap, and the presence of gaps.

4. The metering device of claim 1, further comprising an optical element configured to adjust the focal region of the pump beam and the probe beam on the sample to greater than 20 µm.

5. The measuring device of claim 4, wherein the focal region of the pump bundle and the probe bundle on the sample is at least the size of the structure under test on the sample.

6. The measuring device of claim 1, wherein the probe beam is incident on the area of ​​the patterned structure covered by the sample, wherein each image of the sample generated by the camera corresponds to the arrival of an acoustic echo from the underlying layer within the patterned structure, for detecting an embedded structure in the underlying layer of the patterned structure.

7. The metering device of claim 1, wherein the at least one modulator modulates the frequency of the at least one pump pulse in the pump bundle and demodulates the frequency for the independent phase lock of each pixel in the multi-pixel array.

8. The measuring device of claim 1, wherein the camera generates a plurality of images of the sample, wherein each image is generated with a different time delay between the at least one pump pulse and the at least one probe pulse.

9. The measuring device as claimed in claim 1, wherein the camera is configured to produce in-phase measurements and to produce 90-degree phase difference measurements.

10. A method for nondestructive metrology of a sample, comprising: generating a pulsed light; irradiating the sample with a pump beam generated using at least a first portion of the pulsed light, the pump beam having at least one pump pulse to cause a transient disturbance in the sample material; irradiating the sample with a probe beam generated using at least a second portion of the pulsed light to generate a reflected probe beam having at least one probe pulse, the reflected probe beam being modulated based on the transient disturbance in the sample material; modulating at least the at least one pump pulse in the pump beam; receiving and demodulating the reflected probe beam with a camera to generate an image of the sample, wherein each image varies with at least one time delay between the at least one pump pulse and the at least one probe pulse, the camera being configured to acquire transient signals from the sample in parallel using a multi-pixel array and independent phase locking for each pixel in the multi-pixel array to generate the image, wherein the camera records the reflection of the sample at each pixel of the image based on the at least one time delay between the at least one pump pulse and the at least one probe pulse. The variation of reflectivity or surface deformation, wherein modulating at least one pump pulse in the pump bundle includes modulating a first frequency of the at least one pump pulse in the pump bundle with a first modulator and modulating a second frequency of the at least one probe pulse with a second modulator, and wherein the independent phase locking for each pixel in the multi-pixel array demodulates the frequency based on a combination of the first frequency and the second frequency; and at least one property of the sample is measured based on the recorded reflectivity or surface deformation of the sample at each pixel according to the at least one time delay between the at least one pump pulse and the at least one probe pulse.

11. The method of claim 10, wherein the at least one property of the sample includes the property of an underlying structure, the underlying structure being three-dimensionally imaged based on the image generated by the different time delays between the at least one pump pulse and the at least one probe pulse.

12. The method of claim 10, wherein the at least one property of the sample includes at least one of alignment, overlap, and the presence of gaps.

13. The method of claim 10, further comprising focusing the pump beam and the probe beam onto the sample in a focal region greater than 20 µm.

14. The method of claim 13, wherein the focal region of the pump bundle and the probe bundle on the sample is at least the size of the structure under test on the sample.

15. The method of claim 10, wherein the probe beam is incident on the area of ​​the patterned structure covered by the sample, wherein each image of the sample generated by the camera corresponds to the arrival of an acoustic echo from the underlying layer within the patterned structure, to detect an embedded structure in the underlying layer of the patterned structure.

16. The method of claim 10, wherein the frequency of the at least one pump pulse in the pump bundle is modulated at least once, and the frequency is demodulated for the independent phase lock of each pixel in the multi-pixel array.

17. The method of claim 10, wherein the camera generates a plurality of images of the sample, wherein each image is generated with a different time delay between the at least one pump pulse and the at least one probe pulse.

18. The method of claim 10, generating in-phase measurement and 90-degree phase difference measurement from the image of the sample received from the camera.

Images