Method and system for detecting a grating structure based on photoacoustic effect

Abstract

The application discloses a method and system for detecting a grating structure based on a photoacoustic effect. The method for detecting the grating structure based on the photoacoustic effect according to the application can comprise the following steps: emitting pump light to a light-transmitting layer, the pump light being absorbed by a light-absorbing layer surface, and a sound wave being excited after being converted into heat, wherein the light-absorbing layer is arranged between the light-transmitting layer and the grating structure, the sound wave being reflected after propagating to the grating structure to form a sound wave reflection signal, and the sound wave reflection signal constituting an acoustic replica carrying feature information of the grating structure in space; and detecting the acoustic replica through the light-transmitting layer by using probe light to obtain the feature information of the grating structure. The method according to the application excites a sound wave based on the photoacoustic effect, the sound wave can penetrate the light-absorbing layer to reach the covered grating structure and return carrying the feature information of the grating structure, and non-contact and non-destructive detection of the grating structure buried by an opaque material is realized.

Description

Technical Field

[0001] This application relates to the field of photoacoustic detection technology, and more specifically to a method and system for detecting grating structures based on photoacoustic effects. Background Technology

[0002] As semiconductor manufacturing processes advance towards smaller linewidths, higher densities, and more stacked layers, alignment marks (e.g., grating structures) are increasingly used in advanced processes. Alignment marks are critical functional components in semiconductor processing, frequently used to precisely position patterns across layers, and are widely applied in core processes such as optical alignment, precision measurement, optical filtering, and optoelectronic devices. The accuracy of alignment mark structural parameters has a decisive impact on device yield and reliability. For example, even minute deviations in grating parameters (such as linewidth variations of tens of nanometers or duty cycle shifts of a few percent) can lead to decreased alignment accuracy or device performance degradation. Therefore, the importance of grating structure inspection is increasingly prominent, and it has become a core element in ensuring process quality control. However, existing mainstream inspection methods are gradually revealing inherent limitations when facing increasingly stringent process requirements.

[0003] Therefore, there is an urgent need for an improved method for the accurate inspection of grating structures to meet the pressing requirements of modern high-end manufacturing for the quality control of grating structures. Summary of the Invention

[0004] To overcome one or more of the shortcomings of existing technologies, this application provides a method and system for detecting grating structures based on photoacoustic effects. According to the method of this application, sound waves are excited based on photoacoustic effects. These sound waves can penetrate the light absorption layer to reach the covered grating structure and carry back characteristic information of the grating structure, thus realizing non-contact, non-destructive testing of gratings buried in opaque materials.

[0005] In a first aspect, this application discloses a method for detecting a grating structure based on photoacoustic effects. The method may include: emitting pump light to a light-transmitting layer, which is absorbed by the surface of a light-absorbing layer and converted into thermally excited acoustic waves, wherein the light-absorbing layer is disposed between the light-transmitting layer and the grating structure; the acoustic waves propagate to the grating structure and are reflected to form an acoustic reflection signal, which spatially constitutes an acoustic replica carrying characteristic information of the grating structure; and using probe light to detect the acoustic replica through the light-transmitting layer to obtain characteristic information of the grating structure.

[0006] According to the method of this application, pump light is used to excite ultra-high frequency sound waves. The ultra-high frequency sound waves penetrate the light absorption layer and propagate to the grating structure buried by the light absorption layer. The grating structure is then reflected to form a sound wave reflection signal. The sound wave reflection signal forms an acoustic replica carrying the characteristic information of the grating structure in space. The characteristic information of the grating structure is obtained by detecting the acoustic replica.

[0007] In one alternative embodiment, the light-transmitting layer may be a light-transmitting substrate.

[0008] In one alternative embodiment, the light-absorbing layer may be an opaque film layer.

[0009] In one alternative embodiment, the sound wave can be an ultra-high frequency sound wave.

[0010] In one alternative embodiment, the frequency range of the sound waves can be 10-100 GHz.

[0011] In one alternative embodiment, the grating structure is a nanoscale grating structure.

[0012] In one alternative embodiment, the linewidth of the grating structure is smaller than the wavelength of the probe light.

[0013] In one alternative embodiment, the linewidth of the grating structure ranges from 75 nanometers to several hundred nanometers.

[0014] In one optional embodiment, the acoustic replica is probed through the light-penetrating layer using a probe light to obtain characteristic information of the grating structure. This further includes: responding to a thickness of the light-absorbing layer being greater than a first threshold, using the probe light to detect the diffraction signal generated by the interface displacement grating formed by the acoustic replica at the interface, and analyzing the detected diffraction signal generated by the interface displacement grating to obtain characteristic information of the grating structure; or responding to a thickness of the light-absorbing layer being less than a second threshold, using the probe light to detect the diffraction signal formed by the refractive index grating generated by stress changes within the light-penetrating layer of the acoustic replica, and analyzing the detected diffraction signal formed by the refractive index grating to obtain characteristic information of the grating structure; or responding to a thickness of the light-absorbing layer being greater than the second threshold and less than the first threshold, determining the signal intensities of the diffraction signal generated by the interface displacement grating and the diffraction signal formed by the refractive index grating generated by strain within the light-penetrating layer, and analyzing the diffraction signal with the stronger signal intensity between the interface displacement grating and the refractive index grating to obtain characteristic information of the grating structure, wherein the first threshold is greater than the second threshold.

[0015] The method of this application enables non-contact, non-destructive testing of nanoscale grating structures covered by opaque materials. Simultaneously, the dual detection mechanism, utilizing diffraction signals generated by interface displacement gratings or diffraction signals generated by refractive index gratings, significantly improves detection sensitivity and reliability.

[0016] In one alternative embodiment, the first threshold may be in the range of 115-140 nanometers.

[0017] In one alternative embodiment, the second threshold may be in the range of 90-115 nanometers.

[0018] In an optional embodiment, using probe light to probe an acoustic replica through a light-penetrating layer to obtain characteristic information of the grating structure may include: coherently amplifying the diffraction signal based on the destructive interference between the background light field and the acoustic diffraction field, wherein the background light field is generated by rough scattering of the probe light on the surface of the light-absorbing layer, the acoustic diffraction field is generated by the acoustic replica diffraction modulation of the probe light, and wherein the diffraction signal is included in the acoustic diffraction field.

[0019] According to the method and system of this application, coherent amplification of the acoustic wave reflection signal is achieved based on the destructive interference between the background light field and the acoustic diffraction field, so that the intensity of the first-order diffraction signal included in the acoustic diffraction field is linearly related to the duty cycle of the grating structure, thereby breaking through the optical diffraction limit and realizing high-sensitivity detection of nanometer-linewidth buried gratings.

[0020] In an optional embodiment, coherent amplification of the diffraction signal in the acoustic diffraction field further includes: coherent amplification of the first-order diffraction signal in the diffraction signal, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and wherein the linewidth of the grating structure is inverted based on the linear relationship.

[0021] In a second aspect, this application discloses a system for detecting a grating structure based on photoacoustic effects. The system may include: an acoustic excitation module configured to emit pump light to a light-transmitting layer, which is absorbed by the surface of a light-absorbing layer and converted into thermally excited acoustic waves. The light-absorbing layer is disposed between the light-transmitting layer and the grating structure. The acoustic waves propagate to the grating structure and are reflected to form an acoustic reflection signal, which spatially constitutes an acoustic replica carrying characteristic information of the grating structure; and a signal detection module configured to use probe light to detect the acoustic replica through the light-transmitting layer to obtain characteristic information of the grating structure.

[0022] In one optional embodiment, the acoustic excitation module may include a laser generator and a beam splitter. The laser excited by the laser generator is split into high-energy light and low-energy light by the beam splitter. The high-energy light is frequency-doubled to form pump light, and the low-energy light forms probe light.

[0023] In one alternative embodiment, the wavelength of the pump light can be half the wavelength of the probe light.

[0024] In an alternative embodiment, the wavelength of the probe light can be equal to the wavelength of the laser.

[0025] In an optional embodiment, the signal detection module may be further configured to: in response to the thickness of the light absorption layer being greater than a first threshold, use a probe light to detect the diffraction signal generated by the interface displacement grating formed at the interface of the acoustic replica and analyze the detected diffraction signal generated by the interface displacement grating to obtain characteristic information of the grating structure; or in response to the thickness of the light absorption layer being less than a second threshold, use a probe light to detect the diffraction signal formed by the refractive index grating generated by the stress change inside the light penetration layer of the acoustic replica and analyze the detected diffraction signal formed by the refractive index grating to obtain structural information of the grating structure; or in response to the thickness of the light absorption layer being greater than the second threshold and less than the first threshold, determine the signal intensities of the diffraction signal generated by the interface displacement grating and the diffraction signal formed by the refractive index grating generated by the strain inside the light penetration layer, and analyze the diffraction signal with stronger signal intensity between the diffraction signal of the interface displacement grating and the diffraction signal of the refractive index grating to obtain characteristic information of the grating structure, wherein the first threshold is greater than the second threshold.

[0026] In an optional embodiment, the signal detection module may be further configured to: coherently amplify the diffraction signal in the acoustic diffraction field based on the destructive interference between the background light field and the acoustic diffraction field, wherein the background light field is generated by the rough scattering of the probe light on the surface of the light absorption layer, and the acoustic diffraction field is generated by the diffraction modulation of the probe light by the acoustic replica.

[0027] In an alternative embodiment, the signal detection module may be further configured to: coherently amplify the first-order diffraction signal in the diffraction signal, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and wherein the linewidth of the grating structure is inverted based on the linear relationship.

[0028] In an alternative embodiment, the signal detection module may include a photodiode configured to acquire a first-order diffraction signal.

[0029] In a third aspect, this application discloses an electronic device. The electronic device may include a processor, a memory, and programs or instructions stored in the memory. These programs or instructions can be executed by the processor to implement the steps of the method described above.

[0030] In a fourth aspect, this application discloses a lithography apparatus including the system described above.

[0031] These and other features and advantages will become apparent from the following detailed description and with reference to the accompanying drawings. It should be understood that the foregoing general description and the following detailed description are illustrative only and do not limit the scope of the claims. Attached Figure Description

[0032] To gain a more detailed understanding of the manner in which the features of this disclosure are described above, reference can be made to the various embodiments for a more specific description of the above-briefly summarized aspects, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only certain typical aspects of this disclosure and should not be considered as limiting its scope, as this description may allow for other equivalent and effective aspects.

[0033] Figure 1 A flowchart of a method for detecting grating structures based on photoacoustic effects according to some embodiments of this application is shown.

[0034] Figure 2 A schematic diagram of the optical path for detecting a grating structure using probe light and pump light according to some embodiments of this application is shown.

[0035] Figure 3 A schematic diagram of a device under test with a grating structure according to some embodiments of this application is shown.

[0036] Figure 4 A block diagram of a system for detecting grating structures based on photoacoustic effects according to some embodiments of this application is shown.

[0037] Figure 5 A schematic diagram of the structure of a lithography apparatus including a system according to some embodiments of this application is shown. Detailed Implementation

[0038] In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the described embodiments. However, it will be apparent to those skilled in the art that the described embodiments can be practiced without some or all of these specific details. In other embodiments, well-known structures or processing steps have not been described in detail to avoid unnecessarily obscuring the concepts of this disclosure.

[0039] In the description of the embodiments disclosed herein, it should be noted that, unless otherwise stated, the term "multiple" means two or more; the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist, for example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone; the character " / " in this document generally indicates that the related objects before and after are in an "or" relationship. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure; the terms “comprising” and “having”, and any variations thereof, in the specification, claims and foregoing description of the drawings of this disclosure are intended to cover non-exclusively encompass.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0042] To make the objectives, technical solutions, and advantages of this application clearer, the application is further described in detail below with reference to specific embodiments and the accompanying drawings. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the described exemplary embodiments. However, it will be apparent to those skilled in the art that the described embodiments can be practiced without some or all of these specific details. In other exemplary embodiments, well-known structures have not been described in detail to avoid unnecessarily obscuring the concepts of this disclosure. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application. Furthermore, the various aspects described in the embodiments can be combined arbitrarily without conflict.

[0043] As semiconductor manufacturing and micro / nano fabrication technologies advance towards higher integration and smaller feature sizes, gratings, as core components for achieving interlayer alignment and controlling optical response, directly determine the device's yield and performance through the accuracy of their structural morphology. Therefore, structural parameter inspection of gratings has become an indispensable key step in process quality control. However, existing mainstream inspection methods are gradually revealing the following inherent limitations when facing increasingly stringent process requirements: First, the resolution is insufficient due to the limitations of optical diffraction.

[0044] Traditional optical microscopy is limited by physical principles, with a resolution lower limit of approximately half the wavelength of the incident light. When the feature dimensions (such as linewidth) of the device under test are much smaller than the wavelength of the probe light, optical diffraction effects will cause severe blurring or even indistinguishability of the image. Although electron microscopy techniques (such as SEM and TEM) can provide extremely high spatial resolution, they typically require specific vacuum environments or destructive sample preparation processes, which cannot meet the needs of modern manufacturing for non-contact, non-destructive, and in-situ online monitoring.

[0045] Second, the opaque covering layer blocks the optical detection path.

[0046] In advanced packaging, multilayer interconnects, and microelectromechanical systems (MEMS), to achieve high-density integration, grating structures are often covered with non-transparent materials such as silicon oxide, silicon nitride, or metal films after patterning. Because these covering layers strongly absorb and shield the probe light, the incident light cannot penetrate to the underlying structure, rendering traditional far-field optical detection methods completely ineffective and making it difficult to extract the size and morphology information of the buried structure.

[0047] In conclusion, there is an urgent need for a detection method that can overcome the dual limitations of optical diffraction limit and medium opacity. This method should be non-destructive, highly sensitive, and have good process compatibility to meet the urgent needs of modern high-end manufacturing for quality control of micro and nano structures.

[0048] To address one or more of the above-mentioned problems, this disclosure provides a method and system for detecting grating structures based on the photoacoustic effect. The method of this application uses the photoacoustic effect to excite ultra-high frequency acoustic waves. These ultra-high frequency acoustic waves can penetrate the light absorption layer to reach the covered grating structure and carry back characteristic information of the grating structure. This overcomes the optical diffraction limit and also achieves non-contact, non-destructive testing of gratings buried in opaque materials. The following will describe this in detail with reference to the accompanying drawings.

[0049] Figure 1 A flowchart of a method 100 for detecting a grating structure based on photoacoustic effects according to some embodiments of this application is shown. In some examples, the method 100 for detecting a grating structure based on photoacoustic effects may be performed by a system for detecting grating structures based on photoacoustic effects. The system for detecting grating structures based on photoacoustic effects will be described below. Figure 4 Let me elaborate.

[0050] like Figure 1 As shown, method 100 may include the following steps.

[0051] In step 105, pump light can be emitted to the light-transmitting layer and absorbed by the surface of the light-absorbing layer. The light is then converted into a thermally excited acoustic wave. The light-absorbing layer is disposed between the light-transmitting layer and the grating structure. The acoustic wave is reflected after propagating to the grating structure to form an acoustic wave reflection signal. The acoustic wave reflection signal constitutes an acoustic replica carrying the characteristic information of the grating structure in space.

[0052] In one alternative embodiment, the pump light and the probe light may be excited from the same light source. See below for further details. Figure 3 This paper illustrates the optical path diagrams of the probe light and pump light to clarify the architecture for photoacoustic effect detection based on the probe light and pump light. Figure 2A schematic diagram of the optical path for detecting a grating structure using probe light and pump light according to some embodiments of this application is shown.

[0053] In one implementation, such as Figure 2 As shown, the pump light and probe light can be excited from the same source (e.g., a pulsed laser). For example, a laser system (e.g., a Ti:sapphire femtosecond laser system) can be used as the source 202, wherein the laser emitted by the source has a center wavelength of 800 nm, a repetition frequency of 1 kHz, a pulse width ≤ 50 femtoseconds, and a single pulse energy ≥ 1 millijoule. Subsequently, a beam splitter 204 can be used to split the laser into two beams, for example, a high-energy beam (e.g., having 80-98% of the laser energy) and a low-energy beam (e.g., correspondingly having 2-20% of the laser energy). As an example, the laser can be split into two independent optical paths with an energy ratio of 95:5 using the beam splitter 204, which respectively undertake the functions of acoustic excitation and signal detection.

[0054] As an example, the high-energy light, accounting for 95% of the beam, serves as the pump light branch. It first passes through an optical delay line composed of mirrors 206, 208, 210, and 212. This optical delay line is used to precisely adjust the time difference between the arrival of the pump light and the probe light at the surface of the device under test, thereby achieving synchronized pump-probe measurements. After passing through the optical delay line, the beam is modulated at a frequency of 500 Hz by a mechanical chopper 214 (e.g., a chopper chopper) for phase-locked amplification or signal synchronization detection to suppress background noise. In some cases, the beam can be modulated externally, for example, by an electro-optic modulator (EOM), an acousto-optic modulator (AOM), or a mechanical chopper. In other cases, the beam can be modulated internally, for example, by Q-switching technology, mode-locking technology, or a gain-on laser diode. Subsequently, the beam is incident on a BBO nonlinear frequency doubling crystal 216, where the center wavelength is converted to 400 nanometers through the second harmonic effect. A beam of light with a center wavelength of 400 nanometers is absorbed by the light-absorbing layer and converted into heat energy to generate ultra-high frequency sound waves (e.g., sound waves in the frequency band of 10-100 GHz). The pump light can then be incident on a specific detection area of ​​the device under test 224 through a reflector 218, a beam combiner 220, and a convex lens 222.

[0055] As an example, 5% of the light is used as the probe light branch, with a center wavelength of 800 nanometers, the same as the laser source. After being reflected by mirror 226, the probe light is combined with the pump light at beam combiner 220. The two beams are then focused by the same convex lens 222 onto the same detection area of ​​the device under test 224.

[0056] like Figure 2As shown, the pump light and probe light are focused onto the same location on the device under test. The pump light is absorbed by the light-absorbing layer, converted into heat energy, and then excites an acoustic wave. In some cases, the excited acoustic wave can be an ultra-high frequency acoustic wave. In some cases, the frequency range of the excited acoustic wave is 10-100 GHz. In this example, the excited acoustic wave propagates to the grating structure buried by the light-absorbing layer and is reflected to form an acoustic wave reflection signal. The acoustic wave reflection signal constitutes an acoustic replica carrying the characteristic information of the grating structure in space. The acoustic replica is an acoustic wave field carrying the characteristic information of the grating structure, formed by the reflection of ultra-high frequency acoustic waves by the buried grating structure; it can also be called an "acoustic hologram".

[0057] like Figure 2 As shown, the pump light and probe light pass through the light-transmitting layer via different optical paths and are focused on the surface of the light-absorbing layer. The pump light excites acoustic waves, such as ultra-high frequency (UHF) waves, on the surface of the absorption layer. These UHF waves propagate deep into the light-absorbing layer. When they encounter a grating structure hidden beneath the light-absorbing layer, the acoustic waves are reflected back, forming an "acoustic replica"—essentially, the acoustic waves create a "shadow" of the underlying grating structure. In some cases, the acoustic waves may cause the interface atoms to vibrate up and down, changing the geometric position of the interface and thus forming a phase-type grating on the surface. In other cases, the acoustic waves may cause changes in the dielectric density inside the light-absorbing layer, changing the refractive index within the light-absorbing layer and thus forming an amplitude / intensity-type grating inside the light-absorbing layer. When the probe light and pump light are illuminating the same location, the probe light cannot hear the sound, but it can sense the two tiny changes caused by the sound waves: 1) Interface displacement signal: The sound waves cause the surface of the light-absorbing layer to vibrate up and down, for example, oscillate with an amplitude of 50-250 picometers (1 picometer = one trillionth of a meter), and the probe light captures this vibration; 2) Strain signal inside the light-penetrating layer: The sound waves form a "refractive index grating" inside the light-penetrating layer, and the probe light diffracts when it passes through, just like seeing something through ripples on the water surface is distorted.

[0058] It is important to note that Figure 2The light source and optical path shown are merely exemplary implementations and should not be construed as limiting the scope of protection of this application. In practical applications, those skilled in the art can flexibly adjust or replace the optical path design according to specific detection requirements, device structure, and other factors, as long as the grating structure that allows the probe light and pump light to be incident on the device under test is achieved. For example, a fiber laser can be used instead of a Ti:sapphire femtosecond laser to reduce system cost and improve integration; different beam splitting ratios (such as 90:10) can be used to balance the excitation efficiency of the pump light and the signal-to-noise ratio of the probe light; an acousto-optic modulator or electro-optic modulator can be used instead of a mechanical chopper to achieve higher frequency modulation and more stable phase synchronization; a differential detection architecture can be introduced to suppress common-mode noise, or a heterodyne interferometric detection scheme can be used to improve weak signal extraction capability. In addition, the beam combining method of the probe light and pump light is not limited to free space beam combining, but can also use fiber optic combiners, waveguide coupling structures, or integrated optical chips. All of the above-mentioned modifications that can use pump light to excite sound waves and use probe light to read acoustic replicas should fall within the protection scope of this application.

[0059] In some optional examples, the optical path coincidence of the probe and pump beams can be calibrated before photoacoustic detection to ensure that the optical path coincidence error is less than 1 μm. For example, the spot center, incident angle, and focusing position of the two beams can be calibrated using a high-precision displacement stage, wavefront sensor, and spot positioning system to ensure that the optical path coincidence error is less than 1 μm, thus guaranteeing the spatial consistency of photoacoustic excitation and detection. As an example, and not a limitation, the following exemplary calibration procedure can be adopted: First, place a beam analyzer at the sample location and observe the spot profiles of the pump and probe beams respectively. Use an electric displacement stage for coarse adjustment to initially make the spot centers coincide. Next, introduce a wavefront sensor to monitor the incident angle deviation of the two beams and adjust the tilt angle of the reflector to make the two wavefronts parallel. Finally, use calibration marks on the same focal plane as the grating structure for fine-tuning of the optical path, and combine confocal microscopy to confirm the spatial coincidence status in real time. After calibration, the spatial overlap error of the two beams can be stably controlled below 1 μm, thereby ensuring that when the acoustic wave excited by the pump light propagates to the grating region, the probe light can read the deformation information of the region with high fidelity, avoiding signal attenuation and mode misjudgment caused by spatial mismatch.

[0060] like Figure 2As shown, the pump light and probe light pass through the light-transmitting layer via different optical paths and are focused on the surface of the light-absorbing layer. In one optional embodiment, the light-transmitting layer can be a transparent substrate, such as glass. In another optional embodiment, the light-absorbing layer can be an opaque film layer, such as a metal layer. For example, when the pump light is incident on the glass-metal interface of the device under test, the photon energy is rapidly absorbed by electrons on the metal surface, triggering instantaneous non-equilibrium thermal energy in the electron gas, resulting in thermal expansion. The thermoelastic effect excited by this process is converted into mechanical stress in a very short time, thereby exciting ultra-high frequency ultrasound with frequencies covering 10-100 GHz.

[0061] The following combination Figure 3 This section will elaborate on the structure of the grating in the device under test.

[0062] Figure 3 A schematic diagram of a device under test (DUT) including a grating structure according to some embodiments of this application is shown. For example... Figure 3 As shown, the device under test includes a light-absorbing layer 325 and a grating structure 330. The grating structure 330 can be an alignment mark. The grating structure 330 may include a plurality of spaced-apart protrusions and grooves, which are alternately arranged to form a pattern with periodic characteristics. In some cases, the grating structure 330 can be a nanometer-scale grating structure. For example, the width of the protrusions of the grating structure 330 (i.e., the linewidth of the grating structure) can be from a few nanometers to a few micrometers, for example, 75 nanometers to 1 micrometer. In one example, the linewidth of the grating structure 330 can be smaller than the wavelength of the probe light. The duty cycle of the protrusions of the grating structure 330 can be from 1 to 90%, for example, 1.3%. The duty cycle F = W / P, where W is the width of the grating protrusion and P is the grating period.

[0063] In one embodiment, such as Figure 3 As shown, a light-absorbing layer 325, such as a metal layer, is deposited above the grating structure 330. The light-absorbing layer has low transmittance or is opaque characteristics at the probe wavelength, thus completely burying the grating structure. In some cases, the thickness of the light-absorbing layer can be 90-150 nanometers. A light-transmitting layer, such as a glass layer, is deposited above the light-absorbing layer 325.

[0064] Those skilled in the art will understand that Figure 3 The grating structure shown is provided merely as an example and is not intended to be limiting. Any other grating structure can be detected using the detection method of this application. The detection method of this application is particularly suitable for buried grating structures.

[0065] In one example, the acoustic replica is an "acoustic hologram" that carries the characteristic information of the grating structure, formed by the reflection of sound waves excited by the laser on the surface of the absorption layer after being reflected by the buried grating structure.

[0066] Subsequently, in step 110, the acoustic replica can be probed through the light-penetrating layer using probe light to obtain characteristic information of the grating structure. In one example, the acoustic replica is an "acoustic hologram" carrying structural information of the grating structure, formed by the reflection of sound waves excited by a laser on the surface of the absorption layer after being buried by the grating structure.

[0067] In one alternative embodiment, the detection method of the acoustic replica can vary based on the thickness of the light-absorbing layer. For example, in response to the thickness of the grating structure being greater than a first threshold, the diffraction signal generated by the acoustic replica forming an interface displacement grating at the interface can be detected using probe light, and the detected diffraction signal generated by the interface displacement grating can be analyzed to obtain characteristic information of the grating structure; or in response to the thickness of the light-absorbing layer being less than a second threshold, the diffraction signal formed by the refractive index grating generated by the stress change inside the light-penetrating layer of the acoustic replica can be detected using probe light, and the detected diffraction signal formed by the refractive index grating can be analyzed to obtain characteristic information of the grating structure.

[0068] When probe light illuminates the interface, it diffracts due to interface displacement modulation. By detecting the diffraction signal generated by the interface displacement and analyzing its intensity or phase changes, the characteristic information of the buried grating structure can be retrieved. When probe light passes through the light-transmitting layer, it is diffracted by an acoustic wave forming a refractive index grating. By detecting the diffraction signal of the refractive index grating and analyzing its intensity or phase changes, the characteristic information of the buried grating structure can be retrieved.

[0069] In some examples, the first threshold can be equal to the second threshold. For example, the first and second thresholds can be 90-140 nanometers, preferably 120 nanometers. By presetting the thickness threshold, the detection mechanism can be adaptively switched for light-absorbing layers of different thicknesses: when the thickness is greater than the threshold, the diffraction signal generated by the interface displacement grating is selected for analysis, i.e., the interface displacement detection mode is activated; when the thickness is less than the threshold, the diffraction signal generated by the refractive index grating is selected for analysis, i.e., the refractive index grating detection mode is activated. This dual-track parallel signal selection strategy avoids measurement errors caused by insufficient acoustic wave penetration due to an excessively thick light-absorbing layer or weak interface signals due to an excessively thin layer, thereby ensuring stable acquisition of high-precision grating structure information throughout the entire thickness range, ensuring the robustness and global adaptability of the detection results.

[0070] In other examples, the first threshold may be greater than the second threshold. When the first threshold is greater than the second threshold, in response to the thickness of the light-absorbing layer being greater than the second threshold but less than the first threshold, the signal intensities of the diffraction signal generated by the interface-displaced grating and the diffraction signal formed by the refractive index grating can be determined separately. The diffraction signal with the stronger signal intensity between the interface-displaced grating and the refractive index grating is then analyzed to obtain structural information about the grating structure.

[0071] This application sets the first threshold to be greater than the second threshold to create a transition range between the thick and thin light-absorbing layers. This avoids frequent switching of the detection mechanism due to thickness fluctuations and ensures that when the light-absorbing layer thickness is in the intermediate transition region, the detection channel with stronger signal strength is always locked, thereby achieving continuous and stable extraction of grating structure information. For example, the range of the first threshold is 115-140 nanometers, preferably 125 or 130 nanometers, and the range of the second threshold is 90-115 nanometers, preferably 100 or 105 nanometers, etc.

[0072] In an alternative embodiment, the diffracted signal can be coherently amplified based on the destructive interference between the background light field and the acoustic diffraction field. The background light field can be generated by rough scattering of the probe light on the surface of the light-absorbing layer. The acoustic diffraction field can be generated by diffraction modulation of the probe light by an acoustic replica. The background light field generated by scattering from the rough surface interferes with the acoustic diffraction field, wherein the intensity of the background light field is much higher than that of the acoustic diffraction field (e.g., two orders of magnitude higher). The destructive interference results in a "negative attenuation" phenomenon, achieving effective amplification of the diffracted signal.

[0073] The diffraction signals in the acoustic diffraction field can include zero-order diffraction signals, first-order diffraction signals, second-order diffraction signals, and so on. In an optional example, the first-order diffraction signal can be coherently amplified based on the destructive interference between the background light field and the acoustic diffraction field, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and the linewidth of the grating structure is inverted based on the linear relationship.

[0074] In one alternative embodiment, a photodiode can be used to acquire the first-order diffraction signal. In some cases, a silicon photodiode can be used.

[0075] The photoacoustic method for detecting grating structures according to this application can successfully bypass the optical shielding effect of the upper opaque material, thereby achieving highly sensitive and non-destructive detection of deeply buried structures, providing a new non-destructive characterization method for micro-nano optoelectronic devices, biosensors, integrated optical chips and other fields.

[0076] The photoacoustic method for detecting grating structures according to this application can achieve accurate detection of grating structures when the linewidth of the grating structure is smaller than the wavelength of the probe light, thus overcoming the limitation of the wavelength of the probe light.

[0077] The method for detecting grating structures based on photoacoustic effect according to this application can achieve breakthrough detection of buried gratings with a linewidth of 75 nanometers (e.g., duty cycle of 1.3%), which improves the resolution by 40 times compared with the prior art.

[0078] The photoacoustic effect-based detection method for grating structures according to this application can perform non-contact, non-destructive testing on nanoscale grating structures covered by light-absorbing layers (e.g., opaque films). At the same time, the dual detection mechanism of diffraction signals induced by interface displacement gratings or diffraction signals generated by refractive index gratings significantly improves detection sensitivity and reliability.

[0079] The method for detecting grating structures based on photoacoustic effect according to this application can obtain the linear relationship between diffraction signal and duty cycle. By destructive interference with the background light field, the signal is amplified, so that the intensity of the first-order diffraction signal included in the acoustic diffraction field is linearly related to the duty cycle of the grating structure, thereby achieving high-sensitivity detection of nanometer-linewidth buried gratings.

[0080] The core detection steps and physical mechanisms of this application have been elaborated in detail from a methodological perspective. Accordingly, this application also constructs a complete detection system to implement the above methods. Figure 4 A block diagram of a system 400 for detecting grating structures based on photoacoustic effects according to some embodiments of this application is shown.

[0081] Reference Figure 4 System 400 may include an acoustic excitation module 405 and a signal detection module 410. Each of these modules may be directly or indirectly connected to or communicate with each other on one or more buses 412. In practice, those skilled in the art may decide whether to configure optional modules in system 400 according to actual needs.

[0082] In one embodiment, the acoustic excitation module 405 can be configured to emit pump light to a light-transmitting layer, where it is absorbed and converted into thermal energy on the surface of a light-absorbing layer to excite acoustic waves. The light-absorbing layer is disposed between the light-transmitting layer and the grating structure. After propagating to the grating structure, the acoustic waves are reflected to form an acoustic reflection signal, which spatially constitutes an acoustic replica carrying characteristic information of the grating structure. In an optional embodiment, the acoustic excitation module may include a laser generator and a beam splitter. The laser excited by the laser generator is split into high-energy light and low-energy light by the beam splitter. The high-energy light is frequency-doubled to form the pump light, and the low-energy light forms the probe light. In an optional embodiment, the wavelength of the pump light can be half the wavelength of the probe light. In an optional embodiment, the wavelength of the probe light can be equal to the wavelength of the laser.

[0083] In one embodiment, the signal detection module 410 may be configured to use probe light to detect the acoustic replica through the light-penetrating layer to obtain feature information of the grating structure. In an optional embodiment, the signal detection module may be further configured to: in response to the thickness of the light-absorbing layer being greater than a first threshold, use probe light to detect the diffraction signal generated by the interface-displacement grating generated by the acoustic replica at the interface and analyze the detected diffraction signal generated by the interface-displacement grating to obtain feature information of the grating structure; or in response to the thickness of the light-absorbing layer being less than a second threshold, use probe light to detect the diffraction signal caused by the refractive index grating generated by the stress change inside the light-penetrating layer of the acoustic replica and analyze the detected diffraction signal of the refractive index grating to obtain feature information of the grating structure; or in response to the thickness of the light-absorbing layer being greater than the second threshold and less than the first threshold, determine the signal intensities of the diffraction signal caused by the interface-displacement grating and the diffraction signal caused by the refractive index grating, respectively, and analyze the diffraction signal with stronger signal intensity among the diffraction signal generated by the interface-displacement grating and the diffraction signal generated by the refractive index grating to obtain feature information of the grating structure, wherein the first threshold is greater than the second threshold. In one optional embodiment, the signal detection module may be further configured to: coherently amplify the diffraction signal in the acoustic diffraction field based on the destructive interference between the background light field and the acoustic diffraction field, wherein the background light field is generated by rough scattering of the probe light on the surface of the light absorption layer, and the acoustic diffraction field is generated by diffraction modulation of the probe light by an acoustic replica. In one optional embodiment, the signal detection module may be further configured to: coherently amplify the first-order diffraction signal in the diffraction signal, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and the linewidth of the grating structure is inverted based on the linear relationship. In one optional embodiment, the signal detection module may include a photodiode configured to acquire the first-order diffraction signal.

[0084] Although Figure 4The diagram illustrates specific modules of system 400, but it should be understood that these modules are exemplary and not restrictive. In different implementations, one or more of these modules may be combined, split, removed, or additional modules may be added. In some implementations, system 400 may also include additional modules.

[0085] Figure 5 A schematic diagram of a lithography apparatus 500 including a system 400 according to an embodiment of the present disclosure is provided. Figure 5 As shown, the photolithography equipment 500 may include, for example: Figure 4 The system shown is 400.

[0086] Those skilled in the art will understand that Figure 5 This is provided merely as an example and is not intended to be limiting.

[0087] The "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers.

[0088] Unless otherwise specified in this application, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0089] Unless otherwise specified, all technical features and preferred features mentioned herein can be combined to form new technical solutions. Although this application has been described with reference to optional embodiments, various modifications can be made and components can be replaced with equivalents without departing from the scope of this application. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for detecting grating structures based on photoacoustic effect, comprising: Pump light is emitted to the light-transmitting layer and absorbed by the surface of the light-absorbing layer. It is then converted into a thermally excited sound wave. The light-absorbing layer is disposed between the light-transmitting layer and the grating structure. The sound wave is reflected after propagating to the grating structure to form a sound wave reflection signal. The sound wave reflection signal constitutes an acoustic replica carrying the characteristic information of the grating structure in space. as well as The acoustic replica is probed through the light-transmitting layer using a probe light to obtain feature information of the grating structure.

2. The method according to claim 1, characterized in that, The light-transmitting layer is a light-transmitting substrate, and the light-absorbing layer is an opaque film layer.

3. The method according to claim 1, characterized in that, The sound wave is an ultra-high frequency sound wave, and the frequency range of the sound wave is 10-100 GHz.

4. The method according to claim 1, characterized in that, The grating structure is a nanoscale grating structure, and the linewidth of the grating structure is smaller than the wavelength of the probe light, wherein the linewidth of the grating structure ranges from 75 nanometers to several hundred nanometers.

5. The method according to claim 1, characterized in that, The method of using the probe light to probe the acoustic replica through the light-transmitting layer to obtain feature information of the grating structure further includes: In response to the thickness of the light-absorbing layer being greater than a first threshold, the diffraction signal generated by the interface displacement grating formed at the interface by the acoustic replica is detected using the probe light, and the detected diffraction signal generated by the interface displacement grating is analyzed to obtain the feature information of the grating structure; or In response to the thickness of the light-absorbing layer being less than a second threshold, the diffraction signal formed by the refractive index grating generated by stress change within the light-transmitting layer of the acoustic replica is detected using the probe light, and the detected diffraction signal is analyzed to obtain characteristic information of the grating structure; or In response to the fact that the thickness of the light absorption layer is greater than the second threshold and less than the first threshold, the signal intensities of the diffraction signal generated by the interface displacement grating and the diffraction signal formed by the refractive index grating generated by the internal strain of the light transmission layer are determined respectively, and the diffraction signal with stronger signal intensity between the diffraction signal of the interface displacement grating and the diffraction signal of the refractive index grating is analyzed to obtain the structural feature information of the grating, wherein the first threshold is greater than the second threshold.

6. The method according to claim 5, characterized in that, The first threshold ranges from 115 to 140 nanometers, and the second threshold ranges from 90 to 115 nanometers.

7. The method according to claim 5, characterized in that, The acoustic replica is probed by the probe light through the light-transmitting layer to obtain feature information of the grating structure, including: Based on the destructive interference between the background light field and the acoustic diffraction field, the diffraction signal is coherently amplified, wherein the background light field is generated by the probe light due to rough scattering on the surface of the light absorption layer, the acoustic diffraction field is generated by the acoustic replica modulating the probe light by diffraction, and wherein the diffraction signal is included in the acoustic diffraction field.

8. The method according to claim 7, characterized in that, Coherent amplification of the diffraction signal in the acoustic diffraction field further includes: The first-order diffraction signal in the diffraction signal is coherently amplified, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and wherein the linewidth of the grating structure is inverted based on the linear relationship.

9. A system for detecting grating structures based on photoacoustic effect, comprising: An acoustic excitation module is configured to emit pump light to a light-transmitting layer, which is absorbed by the surface of a light-absorbing layer and converted into a thermally excited acoustic wave. The light-absorbing layer is disposed between the light-transmitting layer and the grating structure. The acoustic wave is reflected after propagating to the grating structure to form an acoustic wave reflection signal. The acoustic wave reflection signal constitutes an acoustic replica carrying characteristic information of the grating structure in space. as well as A signal detection module is configured to use probe light to probe the acoustic replica through the light-transmitting layer in order to obtain structural feature information of the grating structure.

10. The system according to claim 9, characterized in that, The acoustic excitation module includes a laser generator and a beam splitter. The laser excited by the laser generator is split into high-energy light and low-energy light by the beam splitter. The high-energy light is frequency-doubled to form the pump light, and the low-energy light forms the probe light.

11. The system according to claim 10, characterized in that, The wavelength of the pump light is half the wavelength of the probe light, and the wavelength of the probe light is equal to the wavelength of the laser.

12. The system according to claim 9, characterized in that, The signal detection module is further configured to: In response to the thickness of the light absorption layer being greater than a first threshold, the diffraction signal generated by the interface displacement grating formed at the interface by the acoustic replica is detected by the probe light, and the diffraction signal generated by the detected interface displacement grating is analyzed to obtain the feature information of the grating structure. or In response to the fact that the thickness of the light absorption layer is less than a second threshold, the diffraction signal formed by the refractive index grating generated by the stress change inside the light penetration layer of the acoustic replica is detected by the probe light, and the detected diffraction signal formed by the refractive index grating is analyzed to obtain the characteristic information of the grating structure. or In response to the fact that the thickness of the light-absorbing layer is greater than the second threshold and less than the first threshold, the signal intensities of the diffraction signal generated by the interface-displacement grating and the diffraction signal formed by the refractive index grating generated by the strain inside the light-penetrating layer are determined respectively, and the diffraction signal with stronger signal intensity between the diffraction signal of the interface-displacement grating and the diffraction signal of the refractive index grating is analyzed to obtain the characteristic information of the grating structure, wherein the first threshold is greater than the second threshold.

13. The system according to claim 12, characterized in that, The signal detection module is further configured to: Based on the destructive interference between the background light field and the acoustic diffraction field, the diffraction signal is coherently amplified, wherein the background light field is generated by the probe light due to rough scattering on the surface of the light absorption layer, the acoustic diffraction field is generated by the acoustic replica modulating the probe light by diffraction, and wherein the diffraction signal is included in the acoustic diffraction field.

14. The system according to claim 13, characterized in that, The signal detection module is further configured to: The first-order diffraction signal in the diffraction signal is coherently amplified, wherein the intensity of the first-order diffraction signal is linearly related to the duty cycle of the grating structure, and wherein the linewidth of the grating structure is inverted based on the linear relationship.

15. The system according to claim 14, characterized in that, The signal detection module includes a photodiode configured to acquire the first-order diffraction signal.

16. An electronic device comprising a processor, a memory, and a program or instructions stored in the memory, the program or instructions being executable by the processor to perform the steps of the method as claimed in any one of claims 1-8.

17. A lithography apparatus comprising the system of any one of claims 9-15.

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