Raman inactive interlayer breathing mode test method of semiconductor wafer

Abstract

The invention provides a Raman inactive interlayer breathing mode testing method of a semiconductor wafer, and relates to the technical field of spectrums.The method comprises the steps that a transition metal chalcogenide is adopted to prepare a multi-layer two-dimensional semiconductor wafer sample on a composite silicon substrate; finding a sample to be tested on the surface of the composite silicon substrate by using an optical microscope, wherein a tested area forms a phonon-optical cavity; utilizing a low-wave-number microscopic Raman spectrometer to test a low-wave-number microscopic Raman spectrum of the sample under the configuration of parallel polarization and cross polarization; and subtracting the low-wave-number microscopic Raman spectrum under the cross polarization configuration from the low-wave-number microscopic Raman spectrum under the parallel polarization configuration to obtain a breathing mode Raman spectrum of the sample, thereby determining the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor sheet sample. The Raman inactive interlayer breathing mode of the multi-layer two-dimensional semiconductor sheet sample can be detected through the strong coupling effect of the phonon cavity and the optical cavity of the multi-layer two-dimensional semiconductor sheet sample on the composite silicon substrate.

Description

Technical Field

[0001] The invention relates to the field of spectral technology, and in particular to a method for testing Raman inactive interlayer breathing modes of semiconductor slices. Background Art

[0002] With the development trend of miniaturization of semiconductor devices, various low-dimensional semiconductor quantum structures have emerged. Two-dimensional semiconductor flakes, mainly transition metal chalcogenides (MX2), have attracted much attention for their rich physical properties, easy manipulation, and the ability to form two-dimensional heterojunctions with sharp interfaces under lattice mismatch and method incompatibility. The common feature of two-dimensional layered materials is that the atoms in the layer are coupled together by covalent bonds, while the layers interact with each other through van der Waals forces. This makes the MX2 flakes show physical properties such as band structures and phonons that vary significantly with the number of layers and interlayer interactions. Among them, phonons are important carriers of heat transport. The two-dimensional characteristics of MX2 flakes lead to the dominant role of low-wavenumber phonon branch dispersion in heat diffusion, which determines the thermal management capabilities of MX2 flake materials and devices. This urgently requires the detection and regulation of low-wavenumber interlayer phonons in MX2 flakes. Experimentally detecting all low-wavenumber interlayer phonons in MX2 flakes is a prerequisite for studying and regulating the properties of phonons in MX2 flakes, and is of great significance in the application of thermal and electrical transport in semiconductor devices.

[0003] The main technical means to detect low-wavenumber phonons include low-wavenumber Raman spectroscopy and Brillouin scattering spectroscopy. For semiconductor devices with N layers of MX2 thin sheets, N layers of MX2 thin sheets usually have (N-1) low-wavenumber interlayer breathing modes, but due to the high symmetry of MX2 crystals, usually half of the low-wavenumber interlayer breathing modes are Raman inactive. The existing detection methods can usually only detect the phonon modes of the Raman active layer, and cannot detect the Raman inactive phonon modes, which greatly limits the detection and understanding of low-wavenumber phonons in two-dimensional semiconductors. Summary of the invention

[0004] The invention provides a method for testing a Raman inactive interlayer breathing mode of a semiconductor slice, which is used to solve the defect that the Raman inactive interlayer breathing mode cannot be directly detected in the prior art.

[0005] The present invention provides a Raman inactive interlayer breathing mode test of a semiconductor slice, comprising:

[0006] Using transition metal chalcogenides as semiconductor materials, multilayer two-dimensional semiconductor thin film samples were prepared on a composite silicon substrate;

[0007] Using an optical microscope, a test area of ​​the multi-layer two-dimensional semiconductor thin film sample is found on the surface of the composite silicon substrate; the test area constitutes a phonon-optical cavity;

[0008] Using a low-wavenumber micro-Raman spectrometer to emit vertically polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a parallel polarization configuration;

[0009] Utilizing the low-wavenumber micro-Raman spectrometer to emit horizontally polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a cross-polarization configuration;

[0010] The low-wavenumber micro-Raman spectrum under the parallel polarization configuration is subtracted from the low-wavenumber micro-Raman spectrum under the cross polarization configuration to obtain the breathing mode Raman spectrum of the multilayer two-dimensional semiconductor thin film sample;

[0011] The Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample is determined according to the breathing mode Raman spectrum.

[0012] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the excitation light wavelength used in the low wavenumber micro-Raman spectroscopy test matches the wavelength corresponding to the C exciton energy of the multilayer two-dimensional semiconductor slice sample.

[0013] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor slice sample is determined according to the breathing mode Raman spectrum, comprising:

[0014] Performing Lorentz fitting on the breathing mode Raman spectrum to obtain the peak position of the breathing mode Raman spectrum;

[0015] Comparing the peak position with the prediction results of a preset linear chain model and a bond polarizability model to obtain a Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample;

[0016] The linear chain model is used to predict the peak position of the interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample;

[0017] The bond polarizability model is used to predict the intensity distribution of the interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample.

[0018] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the linear chain model is used to calculate the peak position Pos(LB of the jth breathing mode of the multilayer two-dimensional semiconductor slice sample. N,N-j ) is predicted as follows:

[0019]

[0020] Among them, α ⊥is the interlayer breathing coupling force constant of the two-dimensional semiconductor thin film sample, c is the speed of light, μ is the atomic mass per unit area of ​​a single-layer two-dimensional semiconductor thin film in the multi-layer two-dimensional semiconductor thin film sample, and N is the number of layers of the multi-layer two-dimensional semiconductor thin film sample.

[0021] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the grating resolution of the low-wavenumber Raman spectrometer is less than 0.3 wavenumber.

[0022] According to the Raman inactive interlayer breathing mode test of the semiconductor thin slice provided by the present invention, the number of layers of the multi-layer two-dimensional semiconductor thin slice sample ranges from 10 to 100, and the two-dimensional size is greater than 2 microns.

[0023] According to the inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the composite silicon substrate comprises a silicon dioxide layer and a silicon crystal layer, and the silicon dioxide layer is formed on the silicon crystal layer.

[0024] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the Raman spectrum range of the breathing mode is 5 to 50 wave numbers.

[0025] According to the Raman inactive interlayer breathing mode test of the semiconductor slice provided by the present invention, the transition metal chalcogenide compound includes molybdenum disulfide, tungsten disulfide, molybdenum selenide, tungsten diselenide and molybdenum ditelluride.

[0026] According to the Raman inactive interlayer breathing mode test of semiconductor slices provided by the present invention, the multilayer two-dimensional semiconductor slice sample is prepared by any one of micromechanical exfoliation, dry transfer or wet transfer.

[0027] The Raman inactive interlayer breathing mode test of semiconductor slices provided by the present invention can detect the Raman inactive interlayer breathing mode by using parallel polarized and cross polarized excitation light and utilizing the strong coupling effect of the phonon cavity and optical cavity of the multilayer two-dimensional semiconductor slice sample itself on the composite silicon substrate. The high degree of spatial overlap between the phonon cavity and the optical cavity enhances the coupling strength between the two, so that the breathing mode between the Raman inactive layers of the multilayer two-dimensional semiconductor slice sample can be detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1It is a schematic diagram of phonon-optical cavity coupling of the Raman inactive interlayer breathing mode testing method of semiconductor slices provided by the present invention;

[0030] Figure 2 It is a schematic diagram of low wave number micro Raman spectroscopy under parallel polarization and cross polarization configurations provided by the present invention;

[0031] Figure 3 is an optical image of a WS2 thin-sheet sample prepared by a micromechanical exfoliation method provided by the present invention;

[0032] Figure 4 It is a schematic diagram of the phonon frequency of the breathing mode of the 20-layer WS2 thin film sample provided by the present invention;

[0033] Figure 5 It is a schematic diagram comparing the theoretical value and test results of the low-wavenumber Raman spectrum of WS2 thin film samples with different numbers of layers provided by the present invention. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In the description of the embodiments of the present application, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0036] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0037] In the embodiments of the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0039] The purpose of the present invention is to provide an effective method for testing the Raman inactive interlayer breathing modes of semiconductor thin slices prepared from transition metal chalcogenides (MX2), which can not only break through the limitations of traditional Raman selection rules, but also has high accuracy within a certain range of MX2 thin slice layers, and is universal to different multilayer two-dimensional semiconductors, and is suitable for the detection of Raman inactive interlayer breathing modes of a variety of multilayer two-dimensional semiconductor samples.

[0040] Specifically, the Raman inactive interlayer breathing mode testing method of a semiconductor wafer provided by an embodiment of the present invention includes:

[0041] S1, using transition metal chalcogenides as semiconductor materials, preparing multilayer two-dimensional semiconductor thin film samples on a composite silicon substrate;

[0042] First, a transition metal chalcogenide is selected as a semiconductor material for preparing a multilayer two-dimensional semiconductor thin slice sample on a composite silicon substrate. On the same composite silicon substrate, there can be one or more multilayer two-dimensional semiconductor thin slice samples prepared, and the number of layers of the multiple two-dimensional semiconductor thin slice samples can be the same or different, which is not specifically limited here.

[0043] Composite silicon substrates can improve the laser reflectivity at the interface between multilayer two-dimensional semiconductor sheets and substrates.

[0044] S2, using an optical microscope to find a test area of ​​the multilayer two-dimensional semiconductor thin film sample on the surface of the composite silicon substrate; the test area constitutes a phonon-optical cavity;

[0045] An optical microscope is used to find a test area of ​​a multi-layer two-dimensional semiconductor thin film sample on the surface of a composite silicon substrate. The multi-layer two-dimensional semiconductor thin films in the test area constitute a phonon-optical cavity.

[0046] The multilayer two-dimensional semiconductor thin film sample on the composite silicon substrate is not only a phonon cavity for the interlayer breathing phonon vibration, but also an optical cavity for the incident excitation light and scattered light. The spatial coupling between the two leads to a strong coupling effect between the phonon cavity and the optical cavity. Figure 1 The coupling diagram of the phonon cavity and the optical cavity is shown in Figure 1 In the embodiment, a multilayer two-dimensional semiconductor thin slice sample 2 prepared by using transition metal chalcogenide is formed on a composite silicon substrate 1. An optical microscope is used to find the multilayer two-dimensional semiconductor thin slice sample area to be tested on the surface of the composite silicon substrate, namely, test area 2. The multilayer two-dimensional semiconductor thin slice sample in test area 2 forms a phonon-optical cavity in which incident excitation light and scattered light are coupled with the interlayer breathing mode in the sample, which is used to test the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin slice sample. The coupling principle of the phonon-optical cavity can be referred to Figure 1 Part 2-1 is a schematic diagram of a partial enlargement of the test area 2.

[0047] S3, using a low-wavenumber micro-Raman spectrometer to emit vertically polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a parallel polarization configuration;

[0048] The low-wavenumber micro-Raman spectrometer is provided with an incident light path and a scattered light path. A polarizer and a half glass sheet whose applicable wavelength range includes a specific wavelength are provided on the incident light path, and an analyzer whose applicable wavelength range includes a specific wavelength is provided on the scattered light path. By adjusting the position and / or angle of the polarizer, a horizontal polarization configuration light path corresponding to vertical polarization excitation light and vertical scattered light and a cross-polarization configuration light path corresponding to horizontal polarization excitation light and vertical scattered light can be configured, thereby testing the low-wavenumber micro-Raman spectrum of area 2 under parallel polarization configuration and cross-polarization configuration.

[0049] When testing the test area 2, a low-wavenumber micro-Raman spectrometer is used to emit vertically polarized excitation light to the test area 2, and the vertically polarized scattered light signal is collected, so as to test the low-wavenumber micro-Raman spectrum of the test area 2 under the parallel polarization configuration. Specifically, by adjusting the focusing knob of the objective lens of the low-wavenumber micro-Raman spectrometer, the first-order Raman signal of the transition metal sulfide compound with the maximum intensity at about 420 wavenumbers is found, and the low-wavenumber micro-Raman spectrum under the parallel polarization configuration is tested under this focusing condition. Among them, the parallel polarization configuration means that the polarization direction of the incident excitation light is parallel to the polarization direction of the scattered light.

[0050] S4, using the low-wavenumber micro-Raman spectrometer to emit horizontally polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a cross-polarization configuration;

[0051] A low-wavenumber micro-Raman spectrometer is used to emit horizontally polarized excitation light to the test area 2, and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area 2 under the cross-polarization configuration. Specifically, half of the glass slide on the incident light path is rotated 45 degrees, and the low-wavenumber micro-Raman spectrum under the cross-polarization configuration is obtained by testing. The cross-polarization configuration refers to the polarization direction of the incident excitation light being perpendicular to the polarization direction of the scattered light.

[0052] In one embodiment, a multilayer two-dimensional semiconductor thin film sample prepared using tungsten disulfide WS2 as a semiconductor material has a low-wavenumber micro-Raman spectrum under parallel polarization configuration and a low-wavenumber micro-Raman spectrum under cross polarization configuration as shown in FIG. Figure 2 As shown. Figure 2 In the figure, LB is the peak position of the breathing mode, and S is the peak position of the shear mode.

[0053] S5, subtracting the low wavenumber micro-Raman spectrum under the cross polarization configuration from the low wavenumber micro-Raman spectrum under the parallel polarization configuration to obtain a breathing mode Raman spectrum of the multilayer two-dimensional semiconductor thin film sample;

[0054] S6, determining the Raman inactive interlayer breathing mode of the multi-layer two-dimensional semiconductor thin film sample according to the breathing mode Raman spectrum.

[0055] The low wavenumber micro-Raman spectrum under the parallel polarization configuration is subtracted from the low wavenumber micro-Raman spectrum under the cross polarization configuration to obtain the breathing mode Raman spectrum of the multilayer two-dimensional semiconductor thin film sample. The breathing mode Raman spectrum includes the Raman active interlayer breathing mode Raman spectrum and the Raman inactive interlayer breathing mode Raman spectrum of the multilayer two-dimensional semiconductor thin film sample.

[0056] Based on the obtained breathing mode Raman spectrum, the Raman inactive interlayer breathing mode of multilayer two-dimensional semiconductor thin film samples can be determined. Transition metal chalcogenide crystals have high symmetry. For common multilayer two-dimensional semiconductor thin films, samples with an even number of layers belong to D 3d Symmetry, samples with an odd number of layers belong to D 3h Symmetry, odd-numbered breathing pattern (LB N,N-i , i=1,3,5,…) is the Raman active layer, and the even-numbered breathing modes (i.e. LB N,N-i , i=2,4,6,…) is a Raman inactive layer.

[0057] Further, determining the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample according to the obtained breathing mode Raman spectrum specifically includes:

[0058] S61, performing Lorentz fitting on the breathing mode Raman spectrum to obtain the peak position of the breathing mode Raman spectrum;

[0059] S62, comparing the peak position with the prediction results of a preset linear chain model and a bond polarizability model to obtain a Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample;

[0060] The linear chain model is used to predict the peak position of the interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample;

[0061] The bond polarizability model is used to predict the intensity distribution of the breathing mode between active layers of the multilayer two-dimensional semiconductor thin film sample.

[0062] The breathing mode Raman spectrum of the multilayer two-dimensional semiconductor flake obtained is a microscopic Raman spectrum in the range of 5 to 50 wave numbers. The peak position of the breathing mode (LB mode) is obtained by Lorentz fitting. The peak position of the breathing mode is compared with the prediction results of the preset linear chain model and bond polarizability model to determine the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor flake sample.

[0063] The preset linear chain model and bond polarizability model are obtained based on the prior data of the breathing mode of the multilayer two-dimensional semiconductor thin film sample. The linear chain model can be used to predict the peak position of all interlayer breathing modes of the multilayer two-dimensional semiconductor thin film sample, and the bond polarizability model can be used to predict the intensity distribution of all interlayer breathing modes of the multilayer two-dimensional semiconductor thin film sample. The prediction results of the linear chain model include the peak position of the Raman active interlayer breathing mode and the peak position of the Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample.

[0064] Furthermore, the linear chain model is used to calculate the peak position Pos(LB N,N-j) is predicted as follows:

[0065]

[0066] Among them, α ⊥ is the interlayer breathing coupling force constant of the two-dimensional semiconductor thin film sample, c is the speed of light, μ is the atomic mass per unit area of ​​a single-layer two-dimensional semiconductor thin film in the multi-layer two-dimensional semiconductor thin film sample, and N is the number of layers of the multi-layer two-dimensional semiconductor thin film sample. For WS2, α ⊥ =8.82×10 19 N·m -3 , μ=4.67×10 -6 kg·m -2 .

[0067] The atomic displacement of the i-th layer of the two-dimensional semiconductor thin film sample is The normalized Raman intensity of the jth breathing mode is in is the Bose-Einstein distribution function, T is the thermodynamic temperature, k B is the Boltzmann constant.

[0068] In some embodiments, the composite silicon substrate includes a silicon dioxide layer (SiO2) and a silicon crystal (Si) layer, and the SiO2 layer is formed on the Si layer. A transition metal chalcogenide is used as a semiconductor material to prepare a multilayer two-dimensional semiconductor thin film sample on a composite silicon substrate (SiO2 / Si substrate). The transition metal chalcogenide includes molybdenum disulfide MoS2, tungsten disulfide WS2, molybdenum selenide MoSe2, tungsten diselenide WSe2 and molybdenum ditelluride MoTe2. Methods for preparing multilayer two-dimensional semiconductor thin film samples include but are not limited to micromechanical exfoliation, dry or wet transfer. Reference Figure 3 , Figure 3 This is an optical image of a multilayer two-dimensional semiconductor thin film sample prepared by micromechanical exfoliation using WS2 as the semiconductor material. Figure 3 The part corresponding to 3-1 shows a two-dimensional semiconductor thin film sample with 20 layers and a lateral size greater than 15 microns, and the part corresponding to 3-2 shows a two-dimensional semiconductor thin film sample with 38 layers and a lateral size greater than 15 microns.

[0069] Furthermore, the number of layers of the multilayer two-dimensional semiconductor thin slice sample to be tested ranges from 10 to 100, and the two-dimensional size is greater than 2 microns. The wavelength of the excitation light used in the low-wavenumber micro-Raman spectroscopy test matches the wavelength corresponding to the C exciton energy of the multilayer two-dimensional semiconductor thin slice sample. Specifically, based on the transmission matrix method and the coupling effect of the phonon cavity and the optical cavity, the backscattering signal of the interlayer breathing mode corresponding to the wavelength of the excitation light in the MX2 thin slice with a specific number of layers on the composite silicon substrate is calculated; in the backscattering signal, the amplitude ratio of the Raman inactive interlayer breathing mode component to the nearby Raman active interlayer breathing mode component is calculated, and the number of MX2 thin slices corresponding to the extreme value of the amplitude ratio is determined, thereby establishing a corresponding relationship between the amplitude ratio and the number of MX2 thin slices; in the actual test, according to the selected semiconductor material and the number of layers of the two-dimensional semiconductor thin slice sample to be tested, the excitation light with a wavelength matching the wavelength corresponding to the C exciton energy of the multilayer two-dimensional semiconductor thin slice sample is selected.

[0070] Taking the preparation of WS2 thin film samples on SiO2 / Si substrate with WS2 as the semiconductor material as an example, an optical microscope is used to find the multilayer two-dimensional semiconductor thin film sample area that needs to be tested on the surface of the SiO2 / Si substrate, and a laser light source with a wavelength matching the wavelength corresponding to the C exciton energy of the multilayer two-dimensional semiconductor thin film that needs to be tested is selected. The microscopic Raman spectrum of the multilayer two-dimensional semiconductor thin film on the SiO2 / Si substrate in the wavenumber range of 5 to 50 is tested using a low-wavenumber micro-Raman spectrometer under parallel polarization and cross-polarization scattering configurations.

[0071] In some embodiments, the grating resolution of the low wavenumber micro-Raman spectrometer used in the test is less than 0.3 wavenumbers; the laser power irradiated to the sample surface during the test is less than 0.3 milliwatts to avoid the heating effect of the laser on the sample; the parallel polarization scattering configuration refers to the polarization direction of the incident excitation light being parallel to the polarization direction of the scattered light, and usually the polarization direction of the incident excitation light is specified as vertical polarization, and the polarization direction of the scattered light is also specified as vertical polarization; the cross-polarization scattering configuration refers to the polarization direction of the incident excitation light being perpendicular to the polarization direction of the scattered light, and usually the polarization direction of the incident excitation light is specified as horizontal polarization direction, and the polarization direction of the scattered light is specified as vertical polarization direction.

[0072] Under the excitation of the excitation light, the WS2 thin film produces an interlayer breathing vibration mode with wave functions extending to all layers, and the vibration direction is perpendicular to the two-dimensional plane. The vibration direction and amplitude are:

[0073]

[0074] t is the thickness of a single layer of two-dimensional semiconductor material, m is the layer index, N is the total number of layers of the two-dimensional semiconductor sheet, and j is the phonon mode index. Since silicon compounds have lower phonon impedance than ordinary two-dimensional semiconductor materials, the phonon impedance mismatch between the two is about -1, that is, the interlayer breathing vibration of the multi-layer two-dimensional semiconductor sheet is localized in the two-dimensional semiconductor sheet and will not be transmitted to the composite silicon substrate. In addition, for the jth interlayer vibration phonon, there is:

[0075]

[0076] Interlayer breathing mode phonons form standing wave vibrations in multilayer two-dimensional semiconductor sheets, which are similar to the vibrations of phonons in an open phonon cavity. Therefore, multilayer two-dimensional semiconductor sheets are phonon cavities for interlayer breathing vibrations.

[0077] In addition, the incident photons will simultaneously excite electron-hole pairs in multi-layer two-dimensional semiconductor films to form C excitons localized in each layer. The interaction between the standing wave-like interlayer breathing phonon vibrations and a series of localized C exciton states can be described by deformation potential, thereby generating scattered photons.

[0078] Since there are significant differences in refractive index between the air-two-dimensional semiconductor slice and the two-dimensional semiconductor slice-composite silicon substrate interfaces, the incident light and scattered light will be reflected and refracted at these two interfaces, causing the forward and reverse light waves to coherently generate optical standing waves localized in the two-dimensional semiconductor slice. Therefore, the multi-layer two-dimensional semiconductor slice is also an optical cavity for the incident light and scattered light.

[0079] The direct overlap of the phononic cavity and the optical cavity in space leads to strong coupling between the phononic cavity and the optical cavity, which directly leads to spatially modulated photon-electron interaction and electron-phonon interaction, which are determined by the incident light, scattered light electric field distribution and interlayer breathing phonon vibration displacement vector, respectively. The coherent superposition of spatially modulated incident photon-electron interaction, electron-phonon interaction and scattered photon-electron interaction periodically modulates the Raman intensity of each interlayer phonon mode. The relative intensities of odd and even branches of interlayer breathing phonons depend on the reflectivity of the two-dimensional semiconductor sheet-composite silicon substrate, as well as the scattering -Incident light The wave vector difference and the interlayer phonon wave vector (q j ), is the complex refractive index of WS2. If Δk = k s -k i and Δq=q j -q j-1If the even-numbered interlayer breathing phonons are equal, the even-numbered interlayer breathing phonons can be excited, thus breaking through the Raman selection rule, so that the Raman inactive interlayer phonons can be detected. The greater the reflectivity of the two-dimensional semiconductor thin film-composite silicon substrate, the closer the relative intensity of the odd-numbered and even-numbered interlayer phonons is to 1.

[0080] For WS2, the C exciton energy is about 2.7eV, corresponding to an excitation light with a wavelength of 460 nanometers. Therefore, an excitation light with a wavelength of 488 nanometers can be used to resonantly excite the WS2 thin film sample and test the WS2 Raman spectral signal of 5 to 50 wave numbers under parallel polarization and cross polarization scattering configurations. The specific steps are as follows:

[0081] First, a polarizer with an applicable wavelength range including 488 nanometers and a half glass slide are placed on the incident light path, wherein the polarization direction of the polarizer is vertical, and the fast axis of the half glass slide is located at the correction 0 degree. At the same time, a polarizer with an applicable wavelength range including 488 nanometers is placed on the scattered light path, and the polarization direction is vertical.

[0082] Secondly, by adjusting the focusing knob of the low-wavenumber microscope Raman objective, the WS2 first-order Raman signal with the maximum intensity at around 420 wavenumbers is found, and under this focusing condition, the WS2 Raman spectrum signal with 5 to 50 wavenumbers under the parallel polarization configuration is tested.

[0083] Then, half of the glass slide on the incident light path was rotated 45 degrees, and the WS2 Raman spectrum signal of 5 to 50 wave numbers under the cross-polarization configuration was tested.

[0084] The breathing mode Raman spectrum of the two-dimensional semiconductor thin film sample is obtained by subtracting the low wavenumber micro-Raman spectrum under the cross polarization configuration from the low wavenumber micro-Raman spectrum under the parallel polarization configuration, and the peak position of the breathing mode is obtained by Lorentz fitting.

[0085] like Figure 4 As shown, Figure 4 Yes Figure 3 Schematic diagram of the phonon frequency of the breathing mode of the 20-layer WS2 flake sample shown in, Figure 4 From left to right in the figure are the prediction results of the peak position of the interlayer breathing mode of the 20-layer WS2 thin film sample by the linear chain model, the test results of the interlayer breathing mode of the 20-layer WS2 thin film sample, and the theoretical results of the active interlayer breathing mode of the 20-layer WS2 thin film sample. Figure 4 Compared with the prediction results of the linear chain model in the leftmost image, it is found that the peak position of the interlayer breathing mode phonon of the 20-layer WS2 flake sample obtained by the test corresponds to the model prediction result. In addition, in addition to the observation of the original Raman active odd-numbered interlayer breathing phonon vibration (such as Figure 4 As shown in the figure on the far right, the original theoretical prediction of Raman inactive even-branch interlayer breathing phonons LB20,20-j (j=2,4,6,…) can also be detected. Therefore, by selecting an excitation light with a wavelength matching the wavelength corresponding to the C exciton energy to resonantly excite a multilayer two-dimensional semiconductor thin film sample on a composite silicon substrate to enhance the phonon cavity-optical cavity coupling effect, the Raman inactive interlayer breathing mode can be tested.

[0086] With the development of van der Waals heterojunction and related device technologies, most two-dimensional semiconductor devices usually contain dozens of layers of semiconductor materials such as MX2. However, current research on low-wavenumber interlayer phonons in MX2 thin films is usually limited to less than 10 layers, which further limits the improvement of thermal and electrical transport performance of two-dimensional semiconductor devices.

[0087] In order to further verify the role of phonon cavity-optical cavity coupling effect in testing Raman inactive interlayer phonon modes, WS2 thin film samples with different numbers of layers (such as 2 layers, 15 layers and 44 layers) can also be prepared on SiO2 / Si composite silicon substrates, and the phonon frequency of the low-wavenumber Raman spectrum of each sample under excitation light can be tested. The test results are as follows Figure 5 As shown, Figure 5 The low-wavenumber Raman spectra of each sample under 488 nm excitation light and the low-wavenumber Raman spectra of 44-layer WS2 flake samples under 458 nm excitation light are shown. ex is the wavelength of the excitation light. Figure 5 In the low-wavenumber Raman spectrum diagram of WS2 flake samples with the same number of layers, the upper curve corresponds to the theoretical value, and the lower curve corresponds to the actual test result. Figure 5 The test results shown in the figure show that in the 2-layer WS2 flake sample, only the Raman active interlayer phonon mode can be detected, and in the 15-layer WS2 flake sample, a Raman inactive even-branch phonon mode LB can be detected. 15,13 . As the number of layers increases further, Δk is approximately equal to Δq, and all Raman forbidden even-branch interlayer phonon modes can be detected. This effect is more significant when the wavelength of the excitation light is close to the wavelength corresponding to the C exciton energy of the WS2 thin film sample. This illustrates that the detection of Raman inactive interlayer breathing modes can be achieved based on the phonon-optical cavity coupling effect. At the same time, it also illustrates that the Raman inactive interlayer breathing mode test method for semiconductor thin film samples provided by the present invention is suitable for the characterization of Raman inactive interlayer breathing modes of various multilayer two-dimensional semiconductor thin film samples.

[0088] The Raman inactive interlayer breathing mode test method of semiconductor slices provided by the present invention has a simple experimental test method, a wide range of adaptability, and high accuracy. First, the strong coupling effect of the phonon cavity and the optical cavity of the multilayer two-dimensional semiconductor slice sample itself on the SiO2 / Si composite silicon substrate is used to test the characterization of the Raman inactive interlayer phonon mode. The complete spatial overlap of the phonon cavity and the optical cavity enhances the coupling strength of the two. The test method does not require an additional microcavity preparation process and is simple and easy to operate.

[0089] Furthermore, the Raman inactive interlayer breathing mode of the two-dimensional semiconductor thin film sample is tested by resonantly exciting the two-dimensional semiconductor thin film sample with an excitation light whose wavelength matches the wavelength corresponding to the C exciton energy of the two-dimensional semiconductor thin film sample. The Raman intensity is significantly enhanced under resonant excitation and is easy to detect. In addition, since the excitons of conventional two-dimensional semiconductor thin film samples are in the visible light range, an ordinary low-wavenumber micro-Raman spectroscopy test system with a visible light band can meet the test requirements and has universal applicability.

[0090] Furthermore, the strong coupling effect between phonon cavities and optical cavities is common in multilayer two-dimensional semiconductor films and is suitable for the characterization of phonon modes between Raman-inactive layers of different two-dimensional semiconductors.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the Raman inactive interlayer breathing mode of a semiconductor wafer, characterized in that: include: Using transition metal chalcogenides as semiconductor materials, multilayer two-dimensional semiconductor thin film samples were prepared on a composite silicon substrate; Using an optical microscope to find a test area of ​​the multi-layer two-dimensional semiconductor thin film sample on the surface of the composite silicon substrate; The test area constitutes a phonon-optical cavity; Using a low-wavenumber micro-Raman spectrometer to emit vertically polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a parallel polarization configuration; Utilizing the low-wavenumber micro-Raman spectrometer to emit horizontally polarized excitation light to the test area and collect vertically polarized scattered light signals to test the low-wavenumber micro-Raman spectrum of the test area in a cross-polarization configuration; The low-wavenumber micro-Raman spectrum under the parallel polarization configuration is subtracted from the low-wavenumber micro-Raman spectrum under the cross polarization configuration to obtain the breathing mode Raman spectrum of the multilayer two-dimensional semiconductor thin film sample; The Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample is determined according to the breathing mode Raman spectrum.

2. The Raman inactive interlayer breathing mode testing method of a semiconductor wafer according to claim 1, characterized in that: The wavelength of the excitation light used in the low-wavenumber micro-Raman spectroscopy test matches the wavelength corresponding to the C exciton energy of the multilayer two-dimensional semiconductor thin film sample.

3. The Raman inactive interlayer breathing mode testing method of a semiconductor wafer according to claim 1, characterized in that: The method of determining the Raman inactive interlayer breathing mode of the multi-layer two-dimensional semiconductor thin film sample according to the breathing mode Raman spectrum comprises: Performing Lorentz fitting on the breathing mode Raman spectrum to obtain the peak position of the breathing mode Raman spectrum; Comparing the peak position with the prediction results of a preset linear chain model and a bond polarizability model to obtain a Raman inactive interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample; The linear chain model is used to predict the peak position of the interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample; The bond polarizability model is used to predict the intensity distribution of the interlayer breathing mode of the multilayer two-dimensional semiconductor thin film sample.

4. The Raman inactive interlayer breathing mode testing method of a semiconductor wafer according to claim 3, characterized in that: The linear chain model predicts the peak position Pos(LB of the jth breathing mode of the multilayer two-dimensional semiconductor thin film sample. N,N-j ) is predicted as follows: Among them, α ⊥ is the interlayer breathing coupling force constant of the two-dimensional semiconductor thin film sample, c is the speed of light, μ is the atomic mass per unit area of ​​a single-layer two-dimensional semiconductor thin film in the multi-layer two-dimensional semiconductor thin film sample, and N is the number of layers of the multi-layer two-dimensional semiconductor thin film sample.

5. The Raman inactive interlayer breathing mode testing method of a semiconductor wafer according to claim 1, characterized in that: The grating resolution of the low-wavenumber Raman spectrometer is less than 0.3 wavenumber.

6. The Raman inactive interlayer breathing mode testing method of a semiconductor wafer according to claim 1, characterized in that: The number of layers of the multi-layer two-dimensional semiconductor thin film sample ranges from 10 to 100, and the two-dimensional size is greater than 2 microns.

7. The method for testing the Raman inactive interlayer breathing mode of a semiconductor wafer according to claim 1, characterized in that: The composite silicon substrate includes a silicon dioxide layer and a silicon crystal layer, wherein the silicon dioxide layer is formed on the silicon crystal layer.

8. The method for testing the Raman inactive interlayer breathing mode of a semiconductor wafer according to claim 1, characterized in that: The Raman spectrum of the breathing mode ranges from 5 to 50 wave numbers.

9. The method for testing the Raman inactive interlayer breathing mode of a semiconductor wafer according to claim 1, characterized in that: The transition metal chalcogenide compounds include molybdenum disulfide, tungsten disulfide, molybdenum selenide, tungsten diselenide and molybdenum ditelluride.

10. The method for testing the Raman inactive interlayer breathing mode of a semiconductor wafer according to claim 1, characterized in that: The multilayer two-dimensional semiconductor thin film sample is prepared by using any one of micromechanical peeling, dry transfer or wet transfer.

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