KR-20260063006-A - DEPTH PROFILING OF SEMICONDUCTOR STRUCTURES USING PICOSECOND ULTRASONICS

Abstract

A method for depth profiling of samples comprising a target region containing lateral structural features is disclosed herein. The method comprises the steps of acquiring measured signals of the sample and analyzing the measured signals to acquire the depth dependence of at least one parameter characterizing the lateral structural features. The measured signals are acquired by iteratively: projecting a pump pulse onto the sample, thereby generating an acoustic pulse that propagates within the target region; Brillouin scattering a probe pulse from the acoustic pulse within the target region; and detecting the scattered component of the probe pulse to acquire the measured signals. In each iteration, a probe pulse is scattered from the acoustic pulse at each depth within the target region, thereby probes the target region at a plurality of depths. The wavelength of the pump pulse is at least about 2 times greater than the lateral range of the lateral structural features.

Inventors

• 골라니, 오리
• 알목, 아이도

Assignees

• 어플라이드 머티리얼즈 이스라엘 리미티드

Dates

Publication Date

20260507

Application Date

20211011

Priority Date

20201012

Claims (20)

1. As a method, A step of projecting an optical pump pulse onto a semiconductor device including a target region, wherein the step of generating an acoustic pulse that propagates within the target region of the semiconductor device—the wavelength of the pump pulse is at least twice as large as the lateral size of a lateral structural feature of the semiconductor device along at least one lateral direction—; A step of projecting an optical probe pulse onto the semiconductor device, wherein the probe pulse undergoes Brillouin scattering from the acoustic pulse within the target region; A step of detecting the scattered component of the probe pulse to acquire the measured signal; and A step of analyzing the measured signal to obtain the depth dependence of at least one parameter characterizing lateral structural features. A method including
2. A method according to claim 1, wherein the direction of propagation of the acoustic pulse within the target region is parallel to a longitudinal dimension of the target region, parameterizing the depth within the semiconductor device, and the probe pulse is configured such that its absorption length in the target region is greater than the size of the target region along the longitudinal dimension.
3. A method according to claim 1, wherein the lateral structural feature appears as at least one of a change in refractive index or a change in sound velocity in the target region along at least one lateral direction.
4. In paragraph 3, the change in refractive index or the change in the speed of sound is due to one or more changes resulting from design in at least one of the geometry, material composition, medium, mass density, density of embedded elements or voids, or spatial arrangement of embedded elements or voids in the target area along at least one lateral direction, and A method wherein the at least one parameter characterizing the lateral structural feature comprises one or more parameters characterizing at least one of the geometry, material composition, medium, mass density, density of embedded elements or voids, or spatial arrangement of embedded elements or voids.
5. A method according to claim 1, wherein in the analysis of the measured signal, a predetermined expected depth dependence of at least one parameter characterizing the lateral structural feature is taken into account.
6. A method according to claim 1, wherein in the analysis of the measured signal, data fitting tools derived using machine learning techniques are used to obtain the depth dependency of the at least one parameter.
7. A method according to claim 1, wherein the step of analyzing the measured signal comprises obtaining at least one of the time dependence of frequency or the time dependence of amplitude of Brillouin oscillations characterizing the scattered component of the probe pulse, and based thereon, obtaining the depth dependence of the at least one parameter characterizing the lateral structural feature.
8. A method according to claim 1, wherein the step of analyzing the measured signal comprises removing the thermal-optical contribution to the measured signal.
9. In claim 1, at least one of the frequency of the pump pulse or the frequency of the probe pulse is for maximizing the intensity of the scattered component of the probe pulse, or A method in which at least one of the pump pulse or the probe pulse is polarized to maximize the intensity of the scattered component of the probe pulse.
10. A method according to claim 1, wherein the pump pulse is configured to induce mechanical deformation in a lateral absorption layer of the semiconductor device and thereby generate each acoustic pulse, and the absorption layer is perpendicular to the longitudinal direction of the target region, parameterizing the depth within the semiconductor device.
11. In claim 10, the absorption layer is a silicon substrate, the duration of the pump pulse and the probe pulse is shorter than 10 psec, and the width of the acoustic pulse is smaller than 300 nm, method.
12. In claim 10, the method wherein the target region comprises the absorption layer.
13. In claim 10, the absorption layer is positioned adjacent to a lateral outer surface of the semiconductor device onto which at least one of the pump pulse or the probe pulse is projected, thereby causing the acoustic pulse to propagate away from the lateral outer surface of the semiconductor device; A method in which the absorption layer is located within the semiconductor device, and thereby the acoustic pulse propagates away from the absorption layer toward a lateral outer surface onto which at least one of the pump pulse or the probe pulse is projected.
14. A method according to claim 1, wherein the target region comprises a plurality of lateral structural features, the plurality of lateral structural features define a composite lateral structural feature, the wavelength of the pump pulse and the wavelength of the probe pulse are configured to allow simultaneous probe of the composite lateral structural feature, and in an operation of analyzing the measured signal, the acquired depth dependence of the at least one parameter characterizing the lateral structural feature is an average depth dependence across the plurality of composite lateral structural features.
15. In claim 14, the semiconductor device is a FinFET, the target region comprises a plurality of pins arranged parallel to each other to form, for example, the composite lateral structural feature, the at least one parameter characterizing the lateral structural feature comprises a parameter corresponding to the average width of the pins, and the pump pulse and the probe pulse are linearly polarized parallel to the elongate dimension of the pins.
16. In claim 14, the semiconductor device is a vertical NAND stack, and the target region includes a plurality of holes protruding into the target region parallel to the longitudinal direction of the target region, the plurality of holes parameterize the depth within the vertical NAND stack, the holes are arranged to form the composite lateral structural feature, and the at least one parameter characterizing the composite lateral structural feature includes a parameter corresponding to the average diameter or average area of the holes.
17. A method according to claim 16, wherein the probe pulse is linearly polarized along a lateral direction parallel to a first direction defined by the rows of a two-dimensional rectangular array or a second direction defined by the columns of the two-dimensional rectangular array, thereby increasing measurement sensitivity along the second direction or the first direction, respectively.
18. In claim 1, the probe pulse is characterized by at least one of a first probe wavelength or a first probe polarization, or at least one of the pump pulses is characterized by a first pump wavelength or a first pump polarization; The above method further comprises, prior to the operation of analyzing the measured signal, the step of repeating the operation of acquiring a plurality of measured signals with respect to (i) a second probe pulse characterized by at least one of a second probe wavelength or a second polarization, or (ii) a second pump pulse characterized by at least one of a second pump wavelength or a second pump polarization, and thereby acquiring a second plurality of measured signals. A method in which, in the operation of analyzing the above-mentioned measured signals, the plurality of measured signals are analyzed together with at least the second plurality of measured signals.
19. As a system, Memory; and It includes a processor coupled to the above memory, and the processor is: Configured to project an optical pump pulse onto a semiconductor device including a target region to generate an acoustic pulse that propagates within the target region of the semiconductor device, wherein the wavelength of the pump pulse is at least twice the lateral size of a lateral structural feature of the semiconductor device along at least one lateral direction; Configured to project an optical probe pulse onto the semiconductor device so that the probe pulse undergoes Brillouin scattering from the acoustic pulse within the target region; It is configured to detect the scattered component of the probe pulse to acquire a measured signal; A system configured to analyze the measured signal to obtain the depth dependency of at least one parameter characterizing the lateral structural feature.
20. A non-transient computer-readable medium comprising instructions, wherein when the instructions are executed by a processing device, the processing device causes: An optical pump pulse is projected onto a semiconductor device including a target region to generate an acoustic pulse that propagates within the target region of the semiconductor device, wherein the wavelength of the pump pulse is at least twice the lateral size of a lateral structural feature of the semiconductor device along at least one lateral direction. Projecting an optical probe pulse onto the semiconductor device so that the probe pulse undergoes Brillouin scattering from the acoustic pulse within the target region; To acquire a measured signal, the scattered component of the probe pulse is detected; and A non-transient computer-readable medium for analyzing the measured signal to obtain the depth dependency of at least one parameter characterizing the lateral structural feature.

Description

Depth Profiling of Semiconductor Structures Using Picosecond Ultrasonics The present disclosure generally relates to depth profiling of samples. Picosecond ultrasound (also referred to as "picosecond laser ultrasound" and "laser picosecond acoustics") is a non-destructive technique that can be used to acquire structural information from thin films and nanostructures. In a typical scenario, an ultrashort optical pulse (commonly referred to as a "pump pulse") can be projected onto the outer surface of the structure. A thin trench of the structure adjacent to and encompassing the outer surface is heated by absorbing the optical pulse. Due to heating, the trench expands, leading to the formation of an acoustic pulse (also referred to as an "elastic strain pulse" or "strain pulse"), which travels into the depth of the structure and away from the outer surface. Upon reaching a boundary surface, such as the opposite side of the thin film or a second layer of a multilayer structure, at least a portion of the acoustic pulse is reflected and propagated back toward the outer surface. A probe signal is projected onto the outer surface so that it is incident upon the outer surface when the acoustic pulse reaches it, for example. The intensity of the probe signal reflected from the outer surface and the reflected component of the probe signal is monitored. From the monitored intensity of the reflected component, one-dimensional structural information regarding the probed structure—for example, the thickness of the layers or the film thickness (when the structure is multilayer)—can be extracted. Aspects of the present disclosure relate to depth profiling of samples employing picosecond ultrasound, according to some embodiments thereof. More specifically, but not exclusively, aspects of the present disclosure relate to picosecond ultrasound-based methods and systems for depth profiling of samples, in particular, semiconductor devices and structures, according to some embodiments thereof. Accordingly, according to aspects of some embodiments, a method for depth profiling of samples is provided. The method includes the following operations: - A step of providing a sample containing a target region. The target region includes lateral structural features. - A step of acquiring multiple measured signals by implementing the following sub-operations multiple times: ■ For example, a step of projecting an optical pump pulse onto a sample to generate an acoustic pulse that propagates within a target region of the sample. The wavelength of the pump pulse is at least about 2 times larger than the lateral range of a lateral structural feature along at least one lateral direction. ■ A step of projecting an optical probe pulse onto a sample so that the probe pulse undergoes Brillouin scattering from an acoustic pulse within a target region. ■ A step of detecting the scattered component of a probe pulse to acquire a measured signal. In each implementation, each probe pulse is scattered from an acoustic pulse at each depth within the target region so that the target region is probed at multiple depths. - A step of analyzing a plurality of measured signals to obtain the depth dependency of at least one parameter characterizing a lateral structural feature. According to some embodiments of the method, the propagation direction of acoustic pulses within a target region is parallel to the longitudinal dimension of the target region. The longitudinal dimension parameterizes the depth within the sample. According to some embodiments of the method, the propagation of acoustic pulses within a target area is intended to allow, for example, depth profiling of the entire target area. According to some embodiments of the method, the probe pulses are configured such that the absorption length of the probe pulses in the target region is greater than the range of the target region along the longitudinal dimension. According to some embodiments of the method, the wavelength of the pump pulse is at least about 2 times larger than the lateral range of the lateral structural feature along any lateral direction (i.e., all lateral directions). According to some embodiments of the method, lateral structural features appear as a change in refractive index and/or a change in the speed of sound in a target region along at least one lateral direction. According to some embodiments of the method, a change in refractive index and/or speed of sound is due to one or more changes in a target region caused by a design along at least one lateral direction (i.e., variations in structure and/or composition determined by the design of the sample). One or more changes may include changes in geometry, material composition, medium, mass density, density of embedded elements and/or voids, and/or spatial arrangement of embedded elements and/or voids in the target region along at least one lateral direction. At least one parameter characterizing a lateral structural feature includ