Carrier concentration detection method and system based on terahertz time-domain spectroscopy, and medium

Abstract

The application provides a carrier concentration detection method and system based on terahertz time-domain spectroscopy, and a medium, the method comprising the following steps: obtaining a reflection time-domain signal of a sample to be measured; Fourier transforming a first reflection peak of the reflection time-domain signal to obtain a first amplitude and / or a first phase; Fourier transforming a second reflection peak of the reflection time-domain signal to obtain a second amplitude and / or a second phase; and solving the carrier concentration of the sample to be measured according to the first amplitude, the second amplitude, a first reflection model, or according to the first phase, the second phase, a second reflection model. The application greatly shortens the detection time of a large batch of wafers, eliminates errors caused by multiple acquisitions from the root, effectively improves the accuracy of detection, provides a powerful advanced characterization tool for the research and quality control of semiconductor materials, and meets the large-scale and high-throughput wafer detection requirements of the semiconductor industry.

Description

Technical Field

[0001] This invention relates to the field of terahertz application technology, specifically to a method, system, and medium for detecting carrier concentration based on terahertz time-domain spectroscopy. Background Technology

[0002] In semiconductor manufacturing and R&D, carrier concentration is a fundamental and critical parameter for evaluating the electrical properties of materials. Achieving high-precision, non-destructive, and rapid detection of carrier concentration is of great significance for improving device performance, optimizing process routes, and reducing production costs.

[0003] Traditional semiconductor carrier concentration detection methods, such as Hall effect testing and four-probe resistance methods, require electrode fabrication and are contact measurements, which can easily damage the sample. While infrared absorption and Raman spectroscopy can achieve non-contact measurements, they have weak responses to low carrier concentrations and limited sensitivity and dynamic range. Furthermore, traditional detection methods require long detection times, which cannot meet the large-scale, high-throughput wafer inspection needs of the semiconductor industry, thus hindering their large-scale industrial application.

[0004] Terahertz time-domain spectroscopy, as a non-invasive and non-ionizing detection method, has the unique advantages of penetrating non-polar media and simultaneously acquiring amplitude and phase information of the electric field. It can infer important parameters of materials such as complex conductivity and dielectric function, and then calculate carrier concentration. Furthermore, terahertz time-domain spectroscopy equipment is easier to integrate with existing production equipment, has a short detection time, and can achieve large-scale detection.

[0005] In the prior art, patent CN114563372B provides a method for measuring the carrier concentration of materials in the terahertz band. It requires measuring the terahertz reference signal without a sample and the terahertz sample signal with a sample. After Fourier transform, the amplitude ratio and phase difference of the two signals are obtained. The complex permittivity and complex conductivity of the material are then inverted. Finally, based on the dependence of complex conductivity on carrier concentration, the carrier concentration of the material at different wavelengths is calculated.

[0006] However, the existing measurement method requires measuring a reference signal without a sample during each test, which means that the same sample needs to be collected twice during the test, reducing the test efficiency, especially when applied to large-scale wafer inspection. Moreover, there are errors caused by changes in test factors or conditions such as sample placement during the two data acquisitions, which reduces the accuracy of the test to some extent. Summary of the Invention

[0007] To address the aforementioned issues, this invention proposes a carrier concentration detection method, system, and medium based on terahertz time-domain spectroscopy. The carrier concentration detection method of this invention is based on the self-comparison of two reflection peaks of the time-domain signal reflected by the sample under test, eliminating the need to test the reference signal when no sample is present. Therefore, only one time-domain signal acquisition is required during detection, significantly improving the detection efficiency in large-scale wafer inspection. Furthermore, by relying on a single data acquisition, the error caused by two acquisitions is eliminated at its source, effectively improving the accuracy of the detection.

[0008] This invention is achieved through the following technical solution:

[0009] On the one hand, the present invention provides a method for detecting carrier concentration based on terahertz time-domain spectroscopy, comprising the following steps:

[0010] Obtain the time-domain reflection signal of the sample under test;

[0011] The first reflection peak of the reflected time-domain signal is subjected to Fourier transform to obtain a first amplitude and / or a first phase; the second reflection peak of the reflected time-domain signal is subjected to Fourier transform to obtain a second amplitude and / or a second phase.

[0012] The carrier concentration of the sample to be tested is determined based on the first amplitude, the second amplitude, and the first reflection model, or based on the first phase, the second phase, and the second reflection model.

[0013] The first reflection model is:

[0014]

[0015] The second reflection model is:

[0016]

[0017] In the formula, The ratio of the first amplitude to the second amplitude. This is the difference between the first phase and the second phase. The reflection coefficient of terahertz waves at the interface between air and the first ion implantation layer. Let be the reflection coefficient of the terahertz wave at the interface from the i-th layer to the (i+1)-th layer. Let be the relative transmittance of the i-th ion implantation layer. Let T be the transfer function of the i-th ion implantation layer, where i = 1, 2, ..., m, and T is the transfer function of the i-th ion implantation layer. j H represents the relative transmittance of the j-th ion implantation layer. j Let p be the transfer function of the j-th ion implantation layer, where j = 1, 2, ..., i, p m+1 This represents the propagation loss of terahertz waves in a high-resistivity silicon layer.

[0018] In this technical solution, the reflection time-domain signal of the sample to be tested is first acquired. This signal can be obtained using any existing reflection-based terahertz time-domain spectrometer. The sample typically includes a high-resistivity silicon layer and one or more ion-implanted layers above it. When the terahertz wave generated by the reflection-based terahertz time-domain spectrometer is incident on the surface of the ion-implanted layer, the wave is reflected and transmitted at the first interface between air and the first ion-implanted layer, at the second interfaces between the ion-implanted layers, and at the third interface between the bottom ion-implanted layer and the high-resistivity silicon layer, and attenuates during this process. Since the ion-implanted layer is typically nanometer-thick, for example, 24 nm, it is impossible to distinguish the reflection signals of the terahertz wave at the first interface and the various second interfaces. Therefore, the obtained reflection time-domain signal of the sample to be tested will show two reflection peaks. The first peak originates from multiple reflections of the terahertz wave at the first and second interfaces, and the second peak originates from the reflection of the terahertz wave at the bottom of the high-resistivity silicon layer.

[0019] In this technical solution, the carrier concentration of the sample under test is calculated based on the first and second reflection peaks of the reflection time-domain signal. Specifically, after obtaining the reflection time-domain signal of the sample under test, a Fourier transform is performed on the first reflection peak of the reflection time-domain signal to obtain the amplitude spectrum and / or phase spectrum of the first reflection peak in the frequency domain, thereby obtaining the first amplitude and / or first phase corresponding to the first reflection peak. Similarly, a Fourier transform is performed on the second reflection peak of the reflection time-domain signal to obtain the amplitude spectrum and / or phase spectrum of the second reflection peak in the frequency domain, thereby obtaining the second amplitude and / or second phase corresponding to the second reflection peak.

[0020] In this technical solution, the carrier concentration of the sample under test can be solved either based on the first amplitude, the second amplitude, and the first reflection model, or based on the first phase, the second phase, and the second reflection model. After substituting the ratio of the amplitude or phase of the two reflection peaks into the first or second reflection model respectively, the carrier concentration can be deduced from the reflection model.

[0021] In this technical solution, by using the amplitude ratio or phase difference corresponding to the two reflection peaks of the reflection time-domain signal and combining it with the reflection model, the carrier concentration of the sample can be solved by acquiring the sample time-domain signal only once, without the need for comparison with the test reference signal. This significantly shortens the detection time of large batches of wafers and eliminates the error caused by multiple acquisitions at the source, effectively improving the accuracy of detection. It provides a powerful and advanced characterization tool for the research and development and quality control of semiconductor materials, and can meet the needs of large-scale, high-throughput wafer detection in the semiconductor industry.

[0022] In this technical solution, after obtaining the amplitude ratio and / or phase difference of the two reflection peaks, the amplitude ratio or phase difference can be substituted into the first or second reflection model, and the carrier concentration can be solved by numerical methods, such as fitting and iteration.

[0023] Furthermore, when solving for the carrier concentration based on the first amplitude, the second amplitude, and the first reflection model, the test amplitude ratio is calculated based on the first amplitude and the second amplitude. An estimated carrier concentration is set, and the estimated carrier concentration is substituted into the first reflection model to calculate the theoretical amplitude ratio. The theoretical amplitude ratio and the test amplitude ratio are fitted together, and the estimated carrier concentration is adjusted until the difference between the theoretical amplitude ratio and the test amplitude ratio is less than a first preset value. The estimated carrier concentration corresponding to the theoretical amplitude ratio is taken as the carrier concentration of the sample to be tested. The test amplitude ratio is calculated by dividing the first amplitude by the second amplitude.

[0024] Specifically, the test amplitude ratio is obtained by calculating the first amplitude and the second amplitude. Since the material type of the sample to be tested is known, an estimated carrier concentration can be determined based on the typical carrier concentration range of the sample to be tested, which serves as the initial carrier concentration. Subsequently, the initial carrier concentration is substituted into the first reflection model for calculation to obtain the theoretical amplitude ratio. The theoretical amplitude ratio and the test amplitude ratio are fitted. If the difference between the two is less than a first preset value, the initial carrier concentration is used as the carrier concentration of the sample to be tested; conversely, if the difference between the two is greater than or equal to the first preset value, the estimated carrier concentration is adjusted, and a new theoretical amplitude ratio is calculated. The difference between the new theoretical amplitude ratio and the test amplitude ratio is then calculated until, after a certain adjustment, the difference between the theoretical amplitude ratio and the test amplitude ratio is less than the first preset value. In this case, the estimated carrier concentration used in the adjustment is used as the carrier concentration of the sample to be tested.

[0025] Similarly, when solving for the carrier concentration based on the first phase, the second phase, and the second reflection model, the test phase difference is calculated based on the first phase and the second phase. An estimated carrier concentration is set, and the estimated carrier concentration is substituted into the second reflection model to calculate the theoretical phase difference. The theoretical phase difference and the test phase ratio are fitted, and the estimated carrier concentration is adjusted until the difference between the theoretical phase difference and the test phase difference is less than a second preset value. The estimated carrier concentration corresponding to the theoretical phase difference is used as the carrier concentration of the sample to be tested. The test phase difference is calculated by subtracting the first phase from the second phase.

[0026] In this technical solution, by adjusting the estimated carrier concentration and substituting it into the model to calculate the theoretical amplitude ratio or theoretical phase difference, and then fitting the difference between the theoretical ratio and the measured ratio, the calculation time of carrier concentration can be effectively shortened by adjusting the estimated carrier concentration until the difference between the two is less than the preset value, thereby further improving the detection efficiency.

[0027] Furthermore, the theoretical amplitude ratio and the test amplitude ratio are fitted using the least squares method, or the theoretical phase difference and the test phase difference are fitted using the least squares method.

[0028] Furthermore, the frequency of the terahertz wave is 0.5THz to 8.0THz. Hertz waves have the advantages of wide bandwidth and high sensitivity, and can more comprehensively cover carrier concentrations that are sensitive to different frequencies. In some preferred embodiments, the frequency of the terahertz wave is 0.5THz to 8.0THz.

[0029] On the other hand, the present invention provides a carrier concentration detection system based on terahertz time-domain spectroscopy, specifically, the system includes:

[0030] A reflection terahertz time-domain spectrometer is used to acquire the reflection time-domain signal of the sample under test.

[0031] The signal processing unit is configured to obtain a first amplitude and / or a first phase based on the first reflection peak of the reflected time-domain signal via Fourier transform, and to obtain a second amplitude and / or a second phase based on the second reflection peak of the reflected time-domain signal via Fourier transform.

[0032] The calculation unit is used to calculate the carrier concentration of the sample under test based on the first amplitude, the second amplitude and the first reflection model, or based on the first phase, the second phase and the second reflection model.

[0033] The output unit is used to output the carrier concentration of the sample to be tested;

[0034] The first reflection model is:

[0035]

[0036] The second reflection model is:

[0037]

[0038] In the formula, The ratio of the first amplitude to the second amplitude. This is the difference between the first phase and the second phase. The reflection coefficient of terahertz waves at the interface between air and the first ion implantation layer. Let be the reflection coefficient of the terahertz wave at the interface from the i-th layer to the (i+1)-th layer. Let be the relative transmittance of the i-th ion implantation layer. Let T be the transfer function of the i-th ion implantation layer, where i = 1, 2, ..., m, and T is the transfer function of the i-th ion implantation layer. j H represents the relative transmittance of the j-th ion implantation layer.j Let p be the transfer function of the j-th ion implantation layer, where j = 1, 2, ..., i, p m+1 This represents the propagation loss of terahertz waves in a high-resistivity silicon layer.

[0039] Furthermore, the reflective terahertz time-domain spectrometer includes:

[0040] A femtosecond laser is used to emit a femtosecond laser beam, which is split into incident light and detection light by a beam splitter.

[0041] A terahertz source is used to generate terahertz waves under the excitation of incident light. The terahertz waves are collimated and focused onto the sample to be tested in the detection area to generate an echo signal with sample information.

[0042] A detector is used to acquire the echo signal based on detection light passing through a delay line;

[0043] The post-processing unit is used to process the echo signal to obtain the reflected time-domain signal.

[0044] During detection, a femtosecond laser emits a femtosecond laser beam, which is split into two beams by a beam splitter: an incident beam and a detection beam. The incident beam is used to excite a terahertz source to generate a terahertz wave, while the detection beam, after passing through a delay line, is used to detect the terahertz echo. The terahertz wave is collimated by a lens, converged by a parabolic mirror, and incident perpendicularly onto the surface of the sample under test. After reflection and transmission within the sample surface and interior, an echo signal is generated and received by a detector. The received echo signal is sampled by the detector and sent to a post-processing unit for data processing to obtain the reflected time-domain signal.

[0045] Furthermore, the system also includes a moving device for driving several test samples to sequentially pass through the detection area of ​​the reflective terahertz time-domain spectrometer.

[0046] Furthermore, the theoretical amplitude ratio and the test amplitude ratio are fitted using the least squares method, or the theoretical phase difference and the test phase difference are fitted using the least squares method, wherein the frequency of the terahertz wave is 0.5THz~8.0THz.

[0047] The present invention also provides a storage medium comprising a stored computer program, wherein, when the computer program is executed, the device containing the storage medium is controlled to perform any of the aforementioned carrier concentration detection methods based on terahertz time-domain spectroscopy.

[0048] Compared with the prior art, the present invention has the following advantages and beneficial technical effects:

[0049] This invention utilizes the amplitude ratio or phase difference corresponding to the two reflection peaks of the reflection time-domain signal, combined with a reflection model, to solve the carrier concentration of the sample by acquiring the sample time-domain signal only once, without the need for comparison with a test reference signal. This significantly shortens the inspection time for large batches of wafers and eliminates the errors caused by multiple acquisitions at the source, effectively improving the accuracy of the inspection. It provides a powerful and advanced characterization tool for the research and development and quality control of semiconductor materials, and can meet the large-scale, high-throughput wafer inspection needs of the semiconductor industry.

[0050] This invention calculates the theoretical amplitude ratio or theoretical phase difference by substituting the estimated carrier concentration into the model, and then fits the difference between the theoretical value and the test value. By adjusting the estimated carrier concentration until the difference between the two is less than the preset value, the calculation time of carrier concentration can be effectively shortened, thereby further improving the detection efficiency.

[0051] Based on the broadband advantage of terahertz waves, this invention can more comprehensively cover carrier concentrations that are sensitive to different frequencies, and will not damage the sample under test during the detection process, thus having broad application value. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 A schematic diagram illustrating the transmission and reflection phenomena of terahertz incident waves when incident on a thin-film semiconductor material, as provided in an embodiment of the present invention.

[0054] Figure 2 This is a schematic flowchart of a carrier concentration detection method based on terahertz time-domain spectroscopy provided in an embodiment of the present invention;

[0055] Figure 3 This is a schematic diagram of the structure of a reflection terahertz time-domain spectrometer used in a carrier concentration detection system based on terahertz time-domain spectroscopy provided in an embodiment of the present invention.

[0056] Figure labeling: 1-Femtosecond laser, 2-Beam splitter, 3-Terahertz source, 4-Delay line, 5-Lens, 6-Parabolic mirror, 7-Detector, 8-Sample to be tested, 9-Post-processing unit, 10-Reflector. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] In the description of this invention, it should be understood that the terms "front", "rear", "left", "right", "up", "down", "vertical", "horizontal", "high", "low", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0059] Thin-film semiconductor materials are typically extremely thin, ranging from nanometers to micrometers, and have fragile physical structures. Traditional contact detection methods, such as the four-probe method, can easily cause scratches or pressure damage to the sample surface, affecting subsequent performance testing and applications. In this application, the detection method based on reflective terahertz time-domain spectroscopy does not require contact with the sample throughout the entire process. By analyzing the reflective time-domain signal, it can preserve the original physical state and electrical properties of the sample to the greatest extent.

[0060] like Figure 1 As shown, thin-film semiconductor materials typically include a high-resistivity silicon layer and at least one ion-implanted layer above the high-resistivity silicon layer. When a terahertz wave generated by a reflection terahertz time-domain spectrometer is incident on the surface of the ion-implanted layer, the terahertz wave will be reflected and transmitted at the first interface between air and the first ion-implanted layer, at the second interfaces between the ion-implanted layers, and at the third interface between the bottom ion-implanted layer and the high-resistivity silicon layer. Since the ion-implanted layer is typically nanometer-thick, it is impossible to distinguish the reflection signals of the terahertz wave at the first interface and the several second interfaces. Therefore, two reflection peaks will appear in the obtained reflection time-domain signal of the sample under test. The first reflection peak comes from multiple reflections of the terahertz wave at the first and second interfaces, and the second reflection peak comes from the reflection of the terahertz wave at the bottom of the high-resistivity silicon layer.

[0061] The following analysis uses a two-layer structure consisting of an ion-implanted layer and a high-resistivity silicon layer as an example to examine the spectral relationship between the first and second reflection peaks in the time-domain reflectometry signal. The thickness of the ion-implanted layer is also considered. The dielectric constant is Thickness of high-resistivity silicon layer dielectric constant ,in The imaginary unit, This indicates the loss of silicon to terahertz waves; the specific loss needs to be measured experimentally.

[0062] like Figure 1 As shown, the reflection coefficient of the terahertz wave at the interface between the air (layer 0) and the ion implantation layer (layer 1) is... Transmission coefficient is The reflection coefficient in the opposite direction is Transmission coefficient is The reflectance at the interface between the ion-implanted layer and the high-resistivity silicon layer (layer 2) is: Transmission coefficient is The reflection coefficient in the opposite direction is Transmission coefficient is Terahertz waves in thickness The loss in the ion implantation layer is At a thickness of The loss in the high-resistivity silicon layer is By definition, these physical quantities can be expressed as:

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] In the formula, The propagation constant reflects the loss and phase shift characteristics of the medium. The angular frequency of the electromagnetic wave. The relative permittivity of the sample is given. Let be the magnetic permeability of the sample. The relative permittivity of semiconductor materials can be obtained from the Drood model, with the relevant formula being:

[0070]

[0071] in, The dielectric constant for high frequencies is 11.9. is the damping coefficient.

[0072] Further, there are:

[0073]

[0074]

[0075] In the formula, It is a constant representing the effective mass of a hole or electron. These represent the electron charge, the vacuum dielectric constant, and the speed of light in a vacuum, respectively. , , , , , , , , This represents the semiconductor carrier concentration. Since the losses in high-resistivity silicon are unknown, therefore... Experimental determination or database acquisition is required.

[0076] When terahertz waves are incident on the sample, they are first reflected and transmitted at the interface between the air and the ion implantation layer. The reflected wave is the first contribution to the first peak of the time-domain signal, and its ratio to the incident wave is... The transmitted wave oscillates within the ion-implanted layer, undergoing reflection and transmission at the upper and lower surfaces, and gradually attenuating. After one reflection at the lower surface of the ion-implanted layer, the transmitted wave is transmitted again at the upper surface, with a ratio of 1 / 3 to the incident wave. The ratio of the transmitted wave after two reflections to the incident wave is... The ratio of the transmitted wave to the incident wave after k reflections is: Here, terahertz waves can be reflected infinitely many times within the ion-implanted layer; therefore, the reflected signal in this part can be expressed as... This is the second contribution of the first peak of the time-domain signal. Therefore, the ratio of the first reflection peak to the incident terahertz wave can be expressed as:

[0077]

[0078] The first term on the right is the reflection coefficient of the terahertz wave at the interface from air into the ion implantation layer, and the second term is the multiple reflections of the terahertz wave in the ion implantation layer.

[0079] Using the same approach, we can obtain the expression for the ratio of the second peak to the incident terahertz wave:

[0080]

[0081] Since the cumulative terms in the above two equations are the sum of an infinite number of geometric series with a common ratio less than 1, the above two equations can be simplified as follows:

[0082]

[0083]

[0084] The relative transmittance of the i-th layer is defined as:

[0085]

[0086] Define the transfer function of the i-th layer as:

[0087]

[0088] in, This represents the i-th ion implantation layer. This represents the (i-1)th ion implantation layer. This represents the thickness of the i-th layer.

[0089] Based on this definition, for an intrinsic silicon wafer containing m ion-implanted layers, the (m+1)th layer is defined as a high-resistivity silicon layer. This can be generalized to express the ratio of the first reflection peak to the incident terahertz wave as:

[0090]

[0091] The ratio of the second reflection peak to the incident terahertz wave is expressed as:

[0092]

[0093] Finally, the amplitude ratio of the first reflection peak to the second reflection peak, which is also the first reflection model, is:

[0094]

[0095] The phase difference between the first and second reflection peaks, i.e., the second reflection model, is as follows:

[0096]

[0097] in, The reflection coefficient of terahertz waves at the interface between air and the first ion implantation layer. Let be the reflection coefficient of the terahertz wave at the interface from the i-th layer to the (i+1)-th layer. Let be the relative transmittance of the i-th ion implantation layer. Let T be the transfer function of the i-th ion implantation layer, where i = 1, 2, ..., m, and T is the transfer function of the i-th ion implantation layer. j H represents the relative transmittance of the j-th ion implantation layer. j Let p be the transfer function of the j-th ion implantation layer, where j = 1, 2, ..., i, p m+1 This represents the propagation loss of terahertz waves in a high-resistivity silicon layer.

[0098] Based on the derived first and second reflection models, the carrier concentration of the sample under test can be determined by the amplitude ratio or phase difference of the first and second reflection peaks in the reflection time-domain signal.

[0099] Example 1

[0100] like Figure 2 The carrier concentration detection method based on terahertz time-domain spectroscopy shown includes the following steps:

[0101] Obtain the time-domain reflection signal of the sample under test;

[0102] The first reflection peak of the reflected time-domain signal is subjected to Fourier transform to obtain a first amplitude and / or a first phase; the second reflection peak of the reflected time-domain signal is subjected to Fourier transform to obtain a second amplitude and / or a second phase.

[0103] The carrier concentration of the sample to be tested is determined based on the first amplitude, the second amplitude, and the first reflection model, or based on the first phase, the second phase, and the second reflection model.

[0104] The first reflection model is:

[0105]

[0106] The second reflection model is:

[0107]

[0108] In the formula, The ratio of the first amplitude to the second amplitude. This is the difference between the first phase and the second phase. The reflection coefficient of terahertz waves at the interface between air and the first ion implantation layer. Let T be the reflection coefficient of the terahertz wave at the interface between the i-th layer and the (i+1)-th layer, where i = 1, 2, ..., m. j H represents the relative transmittance of the j-th ion implantation layer. j Let p be the transfer function of the j-th ion implantation layer, where j = 1, 2, ..., i, p m+1 This represents the propagation loss of terahertz waves in a high-resistivity silicon layer.

[0109] In the reflection model, the relative transmittance T and transmission coefficient H are related to the reflection coefficient r, transmission coefficient t, and propagation loss p, while the reflection coefficient r and transmission coefficient t of each layer are related to the dielectric constant. Relatedly, the dielectric constant of the air layer is known, the dielectric constant of the high-resistivity silicon layer can be measured experimentally, and the dielectric constant of one or more ion-implanted layers can be obtained by substituting the estimated carrier concentration into the Drood model. Therefore, by adjusting the estimated carrier concentration, different theoretical amplitude ratios or phase differences can be obtained based on the reflection model. Then, by using numerical methods such as fitting and iteration to process the theoretical and measured values, the carrier concentration corresponding to the theoretical value that is close to the measured value can be taken as the carrier concentration of the sample under test.

[0110] In the reflection model, the propagation loss of terahertz waves in the ion implantation layer can be achieved through... We obtain, where The propagation loss of terahertz waves in high-resistivity silicon layers... Or, taking a single ion-implanted layer as an example, propagation loss... The value can be obtained from known data, or it can be obtained before testing by testing a high-resistivity silicon material with a known thickness d' using the following test method. Once obtained, it does not need to be repeated in subsequent tests. Specifically:

[0111] The amplitude of the first reflection peak in the time-domain signal generated when a terahertz wave is focused onto a high-resistivity silicon of known thickness d' The amplitude of the second reflection peak for:

[0112]

[0113]

[0114] in, This indicates the intensity of the incident terahertz wave. This represents the reflection coefficient of terahertz waves entering the interface of high-resistivity silicon from air. The transmission coefficient of a terahertz wave incident from air into high-resistivity silicon. The transmission coefficient of a terahertz wave incident from high-resistivity silicon to air. The propagation loss of terahertz waves propagating through a high-resistivity silicon layer can be further expressed as: This allows the amplitude to be and amplitude ratio Determined as:

[0115]

[0116] After processing, the relationship between propagation loss and frequency f is obtained:

[0117]

[0118] During detection, terahertz waves were observed at a thickness of [missing information]. The propagation loss in a high-resistivity silicon layer can be expressed as .

[0119] In some preferred embodiments, the frequency of the terahertz wave is 0.5THz to 8.0THz.

[0120] In some preferred embodiments, the carrier concentration is solved using a first amplitude, a second amplitude, and a first reflection model, resulting in higher accuracy.

[0121] In this embodiment, after obtaining the amplitude ratio and / or phase difference of the two reflection peaks, the amplitude ratio or phase difference can be substituted into the first or second reflection model, and the carrier concentration can be solved by numerical methods, such as fitting or iteration.

[0122] Example 2

[0123] Based on Example 1, the test amplitude ratio is calculated based on the first amplitude and the second amplitude. An estimated carrier concentration is set, and the estimated carrier concentration is substituted into the first reflection model to calculate the theoretical amplitude ratio. The theoretical amplitude ratio and the test amplitude ratio are fitted together, and the estimated carrier concentration is adjusted until the difference between the theoretical amplitude ratio and the test amplitude ratio is less than a first preset value. The estimated carrier concentration corresponding to the theoretical amplitude ratio is used as the carrier concentration of the sample to be tested. The test amplitude ratio is calculated by dividing the first amplitude by the second amplitude.

[0124] Alternatively, the test phase difference can be calculated based on the first phase and the second phase. An estimated carrier concentration is set, and the estimated carrier concentration is substituted into the second reflection model to calculate the theoretical phase difference. The theoretical phase difference and the test phase difference are fitted together, and the estimated carrier concentration is adjusted until the difference between the theoretical phase difference and the test phase difference is less than a second preset value. The estimated carrier concentration corresponding to the theoretical phase difference is used as the carrier concentration of the sample to be tested, and the test phase difference is calculated by subtracting the first phase from the second phase.

[0125] In some preferred embodiments, the theoretical amplitude ratio and the test amplitude ratio are fitted using the least squares method, or the theoretical phase difference and the test phase difference are fitted using the least squares method.

[0126] Example 3

[0127] Based on the above embodiments, a carrier concentration detection system based on terahertz time-domain spectroscopy is provided, comprising:

[0128] A reflection terahertz time-domain spectrometer is used to acquire the reflection time-domain signal of the sample under test.

[0129] A signal processing unit is configured to obtain a first amplitude and / or a first phase based on the first reflection peak of the reflected time-domain signal, and to obtain a second amplitude and / or a second phase based on the second reflection peak of the reflected time-domain signal.

[0130] The calculation unit is used to calculate the carrier concentration of the sample under test based on the first amplitude, the second amplitude and the first reflection model, or based on the first phase, the second phase and the second reflection model.

[0131] The output unit is used to output the carrier concentration of the sample to be tested;

[0132] In some preferred embodiments, such as Figure 3 As shown, the reflection-type terahertz time-domain spectrometer includes:

[0133] Femtosecond laser 1 is used to emit femtosecond laser light, which is split into incident light and detection light by beam splitter 2;

[0134] Terahertz source 3 is used to generate terahertz waves under the excitation of incident light. The terahertz waves are collimated by lens 5 and then focused by parabolic mirror 6 onto the sample 8 to be tested in the detection area to generate an echo signal with sample information.

[0135] Detector 7 is used to collect the echo signal based on the detection light passed through delay line 4 and reflector 10;

[0136] The post-processing unit 9, for example, employs a computer, to process the echo signal to obtain the reflected time-domain signal.

[0137] In one or more embodiments, during detection, a femtosecond laser 1 emits a 50MHz femtosecond laser beam, which is split into two beams by a beam splitter 2. The incident light excites a terahertz source 3 to generate a terahertz wave with a frequency range of 0.5~8THz. The detection light passes through a delay line 4 to detect the terahertz echo signal. The terahertz wave is collimated by an optical path using a lens 5 with a focal length of 5cm and a parabolic lens 6 with a focal length of 10.16cm. It is incident perpendicularly onto the surface of the sample 8 under test. After reflection and transmission on the surface and inside the sample, a terahertz echo signal is generated and received by a detector 7 with a sampling frequency of 500THz.

[0138] In this embodiment, terahertz waves are used to irradiate the surface of the thin-film semiconductor sample. By receiving and analyzing the time-domain signal reflected from the sample, the carrier concentration of the sample is obtained. When the terahertz wave interacts with the thin-film semiconductor, the carriers will produce modulation effects such as absorption, dispersion, and reflection of the terahertz wave. These effects have a clear quantitative correlation with the carrier concentration. Combined with theoretical derivations such as the Drood model, the constructed first and second reflection models can be used to achieve rapid and accurate detection of the carrier concentration.

[0139] In some preferred embodiments, the system further includes a moving device for driving several test samples sequentially through the detection area of ​​the reflective terahertz time-domain spectrometer.

[0140] In one or more embodiments, the moving device may be a conveyor belt loaded with several samples to be tested. Each sample to be tested is driven by the conveyor belt and passes sequentially through the detection area converged by the parabolic mirror, so that the reflection time-domain signal of each sample to be tested can be collected by the reflection terahertz time-domain spectrometer for subsequent carrier concentration calculation.

[0141] In one or more embodiments, the mobile device may also be an industrial robotic arm, which uses the end effector of the industrial robotic arm to move the sample to be tested sequentially to the detection area to collect its reflection time domain signal.

[0142] Example 4

[0143] Based on the above embodiments, a storage medium is provided, the storage medium including a stored computer program, wherein, when the computer program is running, the device where the storage medium is located is controlled to execute the carrier concentration detection method based on terahertz time-domain spectroscopy shown in any of the foregoing embodiments.

[0144] In this embodiment, the aforementioned storage medium is a computer-readable storage medium. If the terahertz time-domain spectroscopy-based carrier concentration detection system is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above-described embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0145] The terms "first," "second," etc., used in this invention (e.g., first amplitude, second amplitude, first reflection model, second reflection model, etc.) are merely for clarity of description and are not intended to restrict any order or emphasize importance. Furthermore, the term "connection" used in this invention, unless otherwise specified, can refer to a direct connection or an indirect connection via other components.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carrier concentration detection method based on terahertz time-domain spectroscopy, characterized by, The method comprises the following steps: acquiring a reflection time domain signal of a sample to be measured; Fourier transforming a first reflection peak of the reflection time domain signal to obtain a first amplitude and / or a first phase; and Fourier transforming a second reflection peak of the reflection time domain signal to obtain a second amplitude and / or a second phase; solving a carrier concentration of the sample to be measured according to the first amplitude, the second amplitude, and a first reflection model, or according to the first phase, the second phase, and a second reflection model; the first reflection model is as follows: the second reflection model is as follows: wherein, is a ratio of the first amplitude to the second amplitude, is a difference between the first phase and the second phase, is a reflection coefficient of the terahertz wave from the interface of the first layer ion implantation layer into the air, is a reflection coefficient of the terahertz wave from the interface of the i-th layer into the i+1-th layer, is a relative transmittance of the i-th layer ion implantation layer, is a transfer function of the i-th layer ion implantation layer, wherein i = 1, 2, …, m, T j is a relative transmittance of the j-th layer ion implantation layer, H j is a transfer function of the j-th layer ion implantation layer, wherein j = 1, 2, …, i, p m+1 is a propagation loss of the terahertz wave in the high-resistance silicon layer; In solving the carrier concentration according to the first amplitude, the second amplitude, and the first reflection model, a test amplitude ratio is calculated based on the first amplitude and the second amplitude, an estimated carrier concentration is set, the estimated carrier concentration is brought into the first reflection model to calculate a theoretical amplitude ratio, the theoretical amplitude ratio and the test amplitude ratio are fitted, the estimated carrier concentration is adjusted until a difference between the theoretical amplitude ratio and the test amplitude ratio is less than a first preset value, and the estimated carrier concentration corresponding to the theoretical amplitude ratio is taken as the carrier concentration of the sample to be measured. In solving the carrier concentration according to the first phase, the second phase, and the second reflection model, a test phase difference is calculated based on the first phase and the second phase, an estimated carrier concentration is set, the estimated carrier concentration is brought into the second reflection model to calculate a theoretical phase difference, the theoretical phase difference and the test phase difference are fitted, the estimated carrier concentration is adjusted until a difference between the theoretical phase difference and the test phase difference is less than a second preset value, and the estimated carrier concentration corresponding to the theoretical phase difference is taken as the carrier concentration of the sample to be measured.

2. The terahertz time-domain spectroscopy-based carrier concentration detection method according to claim 1, characterized by, The least square method is used to fit the theoretical amplitude ratio and the test amplitude ratio, or the least square method is used to fit the theoretical phase difference and the test phase difference.

3. The terahertz time-domain spectroscopy-based carrier concentration detection method according to any one of claims 1 to 2, characterized by, The frequency of the terahertz wave is 0.5 THz to 8.0 THz.

4. A carrier concentration detection system based on terahertz time-domain spectroscopy, characterized by, The system comprises: a reflection type terahertz time domain spectrometer configured to acquire a reflection time domain signal of a sample to be measured; a signal processing unit configured to acquire a first amplitude and / or a first phase by Fourier transforming a first reflection peak of the reflection time domain signal, and acquire a second amplitude and / or a second phase by Fourier transforming a second reflection peak of the reflection time domain signal; a calculation unit configured to calculate a carrier concentration of the sample to be measured based on the first amplitude, the second amplitude, and a first reflection model, or based on the first phase, the second phase, and a second reflection model; an output unit configured to output the carrier concentration of the sample to be measured; the first reflection model is as follows: the second reflection model is as follows: In solving the carrier concentration according to the first amplitude, the second amplitude, and the first reflection model, a test amplitude ratio is calculated based on the first amplitude and the second amplitude, an estimated carrier concentration is set, the estimated carrier concentration is brought into the first reflection model to calculate a theoretical amplitude ratio, the theoretical amplitude ratio and the test amplitude ratio are fitted, the estimated carrier concentration is adjusted until a difference between the theoretical amplitude ratio and the test amplitude ratio is less than a first preset value, and the estimated carrier concentration corresponding to the theoretical amplitude ratio is taken as the carrier concentration of the sample to be measured. In solving the carrier concentration according to the first phase, the second phase, and the second reflection model, a test phase difference is calculated based on the first phase and the second phase, an estimated carrier concentration is set, the estimated carrier concentration is brought into the second reflection model to calculate a theoretical phase difference, the theoretical phase difference and the test phase difference are fitted, the estimated carrier concentration is adjusted until a difference between the theoretical phase difference and the test phase difference is less than a second preset value, and the estimated carrier concentration corresponding to the theoretical phase difference is taken as the carrier concentration of the sample to be measured. wherein, is a ratio of the first amplitude to the second amplitude, is a difference between the first phase and the second phase, is a reflection coefficient of the terahertz wave from the interface of the first ion implantation layer into the air, is a reflection coefficient of the terahertz wave from the interface of the i-th layer into the i+1-th layer, is a relative transmittance of the i-th ion implantation layer, is a transfer function of the i-th ion implantation layer, wherein i = 1, 2, …, m, T j is a relative transmittance of the j-th ion implantation layer, H j is a transfer function of the j-th ion implantation layer, wherein j = 1, 2, …, i, p m+1 is a propagation loss of the terahertz wave in the high-resistance silicon layer; The computing unit, when solving the carrier concentration according to the first amplitude, the second amplitude and the first reflection model, calculates a test amplitude ratio based on the first amplitude and the second amplitude, sets an estimated carrier concentration, brings the estimated carrier concentration into the first reflection model to calculate a theoretical amplitude ratio, fits the theoretical amplitude ratio and the test amplitude ratio, adjusts the estimated carrier concentration until a difference between the theoretical amplitude ratio and the test amplitude ratio is less than a first preset value, and regards an estimated carrier concentration corresponding to the theoretical amplitude ratio as the carrier concentration of the sample to be measured. Or the computing unit, when solving the carrier concentration according to the first phase, the second phase and the second reflection model, calculates a test phase difference based on the first phase and the second phase, sets an estimated carrier concentration, brings the estimated carrier concentration into the second reflection model to calculate a theoretical phase difference, fits the theoretical phase difference and the test phase difference, adjusts the estimated carrier concentration until a difference between the theoretical phase difference and the test phase difference is less than a second preset value, and regards an estimated carrier concentration corresponding to the theoretical phase difference as the carrier concentration of the sample to be measured.

5. The terahertz time-domain spectroscopy-based carrier concentration detection system of claim 4, wherein, The reflection type terahertz time domain spectrometer comprises: a femtosecond laser for emitting femtosecond laser, the femtosecond laser is split by a beam splitter to obtain incident light and detection light; a terahertz source for generating terahertz waves under the excitation of the incident light, the terahertz waves are focused on the sample to be measured in the detection area after collimation, and a return signal with sample information is generated; a probe for collecting the return signal based on the detection light through a delay line; a post-processing unit for processing the return signal to obtain the reflection time domain signal.

6. The terahertz time-domain spectroscopy-based carrier concentration detection system of claim 5, wherein, The system further comprises a moving device for driving a plurality of samples to be measured to pass through the detection area of the reflection type terahertz time domain spectrometer in turn.

7. The terahertz time-domain spectroscopy based carrier concentration detection system according to any one of claims 4 to 6, characterized in that, The least square method is used to fit the theoretical amplitude ratio and the test amplitude ratio, or the least square method is used to fit the theoretical phase difference and the test phase difference, and the frequency of the terahertz wave is 0.5 THz-8.0 THz.

8. A storage medium, characterized by The storage medium comprises a stored computer program, wherein when the computer program runs, the device where the storage medium is located performs the carrier concentration detection method based on terahertz time domain spectroscopy according to any one of claims 1-3.

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