Asynchronous reference differential reflection spectrum system and method for MOCVD (Metal Organic Chemical Vapor Deposition) rotary sample table

Abstract

The invention relates to an asynchronous reference differential reflection spectrum system and method for an MOCVD (Metal Organic Chemical Vapor Deposition) rotary sample stage, and the system comprises a light source module which is used for generating a broadband spectrum light beam, the light source module comprises a halogen tungsten lamp, an LED (Light Emitting Diode) and an optical fiber beam combiner, two paths of light sources are coupled through the optical fiber beam combiner to form a broadband light source, and the light source intensity at the wave band of 400-800 nm is ensured to be proper; the incident light path module is used for aligning the light beam to the surface of a sample in the MOCVD cavity; the reference light path module is used for carrying out intensity calibration on the light beams emitted by the light source; the reflected light path module is used for converging the reflected light of the measuring light path and the reflected light of the reference light path and transmitting the converged light to the spectrum detection component; and the signal processing module is used for performing light intensity threshold judgment, spectrum average value calculation and differential reflection spectrum calculation.

Description

Technical Field

[0001] This invention belongs to the field of optical measurement technology and relates to efficient, high-precision, and highly stable in-situ optical measurement technology for two-dimensional materials, semiconductor nanofilms, film thickness, optical constants, and key parameters of film growth of typical semiconductors. In particular, it relates to an asynchronous reference differential reflectance spectroscopy system and method for MOCVD rotating sample stages. Background Technology

[0002] Metal-organic chemical vapor deposition (MOCVD) is an important epitaxial growth method widely used in the fabrication of semiconductor thin film materials, particularly in compound semiconductors, two-dimensional materials, and novel optoelectronic devices. The MOCVD thin film growth process is highly dependent on the precise control of process parameters such as temperature, gas flow rate, and reaction pressure. Even minute changes in film thickness, refractive index, and coverage can significantly affect device performance. Therefore, implementing a rapid, non-destructive, and non-contact in-situ monitoring system during the growth process is crucial. This system can not only capture anomalies in real time but also accurately monitor the growth rate and thickness changes of the epitaxial wafer, providing a quantitative basis for the control of the epitaxial growth process and ultimately contributing to the fabrication of higher-quality thin film materials.

[0003] In-situ monitoring in MOCVD systems is primarily based on optical methods suitable for moderate pressure conditions and various gas environments. Currently, in-situ thickness monitoring techniques for MOCVD-grown thin films mainly employ reflection methods based on interference effects, calculating film thickness by monitoring changes in single-wavelength laser light or broadband reflectivity. However, this method is susceptible to long-term light source drift, environmental disturbances, and noise interference. These problems are even more pronounced under the conditions of a rapidly rotating MOCVD sample stage, making it difficult to achieve high-precision, high-stability real-time monitoring of atomically thin films.

[0004] In summary, existing optical reflectance spectroscopy systems cannot achieve low-cost, long-term, highly stable, and high-precision in-situ measurements of ultrathin films grown in the rotating sample stage of MOCVD, resulting in the inability of spectral reflectance methods to meet the high-accuracy measurement requirements of thin film growth. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes an asynchronous reference differential reflectance spectroscopy system and method for MOCVD rotating sample stages. By employing a highly stable, wide-spectrum light source to reduce high-frequency signal fluctuations, and simultaneously introducing an asynchronous reference optical path, the influence of long-term light source drift on measurement results is effectively suppressed. This system meets the high stability and high sensitivity measurement requirements of MOCVD thin film growth. The technical solution is as follows: An asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage, characterized in that it comprises: The light source module is used to generate a broadband light beam. The light source module includes a halogen tungsten lamp, an LED, and an optical fiber combiner. The two light sources are coupled through the optical fiber combiner to form a broadband light source, ensuring that the light source intensity in the 400 nm to 800 nm band is appropriate. The incident light path module is used to collimate the above-mentioned light beam to the sample surface inside the MOCVD cavity; The reference optical path module is used to calibrate the intensity of the beam emitted by the light source; The reflected light path module is used to converge and transmit the reflected light from the measurement light path and the reflected light from the reference light path to the spectral detection component; The signal processing module is used to determine the light intensity threshold, calculate the average spectral value, and calculate the differential reflectance spectrum.

[0006] Furthermore, the incident optical path module includes a collimator, a plano-convex lens, an aperture, and a beam splitter; the collimator is used to convert the diverging beam emitted from the optical fiber into an approximately collimated beam; the plano-convex lens is used to improve the collimation of the beam; the aperture is used to adjust the beam size; the beam splitter is used to reflect the incident beam to the reference optical path, transmit it to the sample surface inside the MOCVD cavity to form a measurement optical path, and reflect and transmit the beams reflected by the sample and the reference sample inside the cavity into the reflection optical path module, respectively.

[0007] Furthermore, the reference optical path module includes an optical shutter and a reference sample; the optical shutter is used to control the opening and closing of the reference optical path. When the optical shutter is closed, the dark noise of the system is measured; when the optical shutter is open, the light intensity signal of the reference path is measured; the reference sample is the same as the blank substrate and is used to reflect the reference light intensity into the reflection optical path module.

[0008] Furthermore, the reflected optical path module includes a short focal length plano-convex lens, a multimode fiber held by a fiber optic holder, and a spectrometer. The short focal length plano-convex lens is used to converge the reflected beam; the multimode fiber held by the fiber optic holder collects the converged beam and incident it into the spectrometer.

[0009] This invention also provides an asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage. The system implementation includes the following steps: S1. Start the light source module, close the light shutter, so that the light beam is incident on the surface of the planetary disk but does not illuminate the sample to be tested, and collect the dark noise of the system; S2. Adjust the incident light path to maximize the intensity of the received reflected light; S3. Open the optical shutter, place the reference sample in the reference optical path module and adjust it to maximize the intensity of the received reflected light; S4. Based on the rotational speed of the planetary disk, determine the number of samples, the light intensity threshold, the number of points required inside the sample to be tested, and the number of points required outside the sample. S5. Perform measurements and use the signal processing module to solve the spectral data of the sample to be tested in the rotating planetary disk: distinguish the reference light and the measurement light signal by the light intensity threshold, calculate the real-time reflectance, and calculate the differential reflectance spectrum based on the initial reflectance. Furthermore, the solution performed by the signal processing module in step S5 includes: Using the light intensity of a specific wavelength as a reference, the light intensity of the reference optical path is distinguished from the light intensity of the superimposed reference optical path of the measurement optical path by using a light intensity threshold. After calculating the average spectral intensity of the reference optical path and the measurement optical path, the reflectance of the sample under test at each time point after one rotation is determined by the ratio of the two values. Since the sample stage is rotating, the average spectral values ​​of the reference optical path and the measurement optical path correspond to different times in each revolution, thus forming an asynchronous reference mode; The difference between the reflectance at the current moment and the reflectance at the initial moment is calculated and normalized to obtain the differential reflectance spectral value for each corresponding moment of each cycle. The specific formula is as follows:

[0010]

[0011] in, For a specific wavelength, For the time corresponding to each rotation, Time shift introduced by rotation, This represents the actual light intensity at the current moment, where the reference optical path and the measurement optical path are superimposed. The actual reference optical path intensity at the current moment. This represents the original light intensity at the current moment, resulting from the superposition of the reference and measurement optical paths. The light intensity of the original reference optical path at the current moment. The system dark noise is measured when the optical shutter is closed, and the reflectivity at each current moment is calculated from this:

[0012] in, Given the reflectance at the current moment, the difference between this reflectance and the reflectance at the initial moment is calculated and normalized to obtain the differential reflectance spectral signal for each corresponding moment of each cycle:

[0013]

[0014] in, The differential reflectance spectrum at the current moment. The reflectance is at the initial moment.

[0015] Furthermore, the specific wavelength is 600 nm.

[0016] Furthermore, in the aforementioned asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage, the planetary disk rotation speed... The calculation formula is as follows:

[0017] in, and These are the times when the edge of the same sample is measured in the nth and (n-1)th cycles, respectively, which are the times when the single-wavelength light intensity signal corresponding to the same sample reaches the preset light intensity threshold.

[0018] The asynchronous reference differential reflectance spectroscopy system and method for MOCVD rotating sample stages proposed in this invention have at least one or a portion of the following beneficial effects: (1) This invention introduces a reference optical path and calculates the ratio of light intensity between the measurement path and the reference path through asynchronous reference, effectively eliminating the influence of long-term light source drift. Measurement can begin without preheating the light source. At the same time, the system only needs one spectrometer to complete signal acquisition, which significantly reduces system complexity and equipment cost.

[0019] (2) By adopting the asynchronous differential spectroscopy method, if the light source intensity is stable during the differential reflectance spectrum calculation process, the actual reflectance spectrum signal of the sample can be measured without relying on the dark noise measurement step. This fundamentally simplifies the traditional differential reflectance spectrum measurement process and significantly improves the system's ease of operation and measurement efficiency.

[0020] (3) The spectral acquisition and processing rate of the present invention can reach the millisecond level, which can meet the requirements for real-time monitoring during the rapid deposition of MOCVD thin films.

[0021] (4) The light source of the present invention covers a wavelength range of 400~800 nm, which can be applied to the growth monitoring of most two-dimensional transition metal sulfide films and has a wide detection range.

[0022] (5) The present invention can also measure the rotational speed of the planetary disk in the MOCVD reaction chamber by combining the signal change law, providing additional functions for monitoring the equipment operation status. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage. (See figure.) 1-Halogen tungsten lamp 2-LED 3-Fiber optic combiner 4-Fiber optic collimator 5-Plan-convex lens 6-Aperture 7-Beam splitter; 8-Optical shutter; 9-Reference sample; 10-Short focal length plano-convex lens 11- Multimode fiber held by a fiber optic clamp 12- Spectrometer 13- Computer 14- Planetary disk Figure 2 The curve shows the variation of the DR value at a wavelength of 500 nm obtained from a 30-minute differential reflectance spectral stability test of a blank sapphire substrate under planetary disk rotation conditions with dark noise subtracted.

[0024] Figure 3 The curve shows the variation of the DR value at 500 nm wavelength obtained from a 30-minute differential reflectance spectral stability test of a blank sapphire substrate under planetary disk rotation conditions without dark noise subtraction.

[0025] Figure 4 The results show the light source stability test results of a blank sapphire substrate under the same conditions. The test duration is 30 min, and the corresponding DR value change curve is shown at a wavelength of 500 nm.

[0026] Figure 5 The results are from the differential reflectance spectroscopy measurements of the sub-monolayer MoS2 thin film.

[0027] Figure 6 This is a real-time in-situ monitoring curve of the DR value of MoS2 films with different thicknesses and coverage at a wavelength of 500 nm during the real-time growth process of MOCVD.

[0028] Figure 7 This is a curve showing the measurement results of the planetary disk rotation speed by this system.

[0029] Figure 8 This is a flowchart of the operation steps of the system and method of the present invention. Detailed Implementation

[0030] This invention provides an asynchronous reference differential reflectance spectroscopy system and method for MOCVD rotating sample stages, enabling real-time measurement of the optical properties of ultrathin thin films at the nanoscale. The system mainly includes a light source module, an incident light path module, a reference light path module, a reflected light path module, and a signal processing module. The light source module outputs a highly stable broadband beam, which is collimated by the incident light path module and incident on the sample surface and the reference light path module within the MOCVD cavity. The beam reflected from the sample and the beam from the reference light path module are then transmitted to the spectrometer via the reflected light path module. The signal processing module performs real-time calculations on the acquired spectral data from the measurement and reference light paths. This invention significantly improves the sensitivity of the signal to changes in the optical properties of nanoscale-thick thin films using differential reflectance spectroscopy, meeting the monitoring requirements for high precision, real-time performance, and stability during the rapid deposition of MOCVD thin films.

[0031] The present invention will be further described below with reference to the accompanying drawings and examples, but this is not intended to limit the scope of protection of the present invention.

[0032] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0033] Certain embodiments of this disclosure will be described more fully below with reference to the accompanying drawings, some of which, but not all, will be shown. In fact, various embodiments of the invention may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to enable the invention to meet applicable legal requirements.

[0034] Example 1: Figure 1 This is a schematic diagram of the asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage according to an embodiment of the present invention, including: 1-halogen tungsten lamp, 2-LED, 3-fiber combiner, 4-fiber collimator, 5-plano-convex lens, 6-aperture, 7-beam splitter, 8-optical shutter, 9-reference sample, 10-short focal length plano-convex lens, 11-multimode fiber held by fiber holder, 12-spectrometer, 13-computer, 14-planetary disk. The polychromatic light generated by the halogen tungsten lamp 1 and LED 2 is transmitted through the fiber optic combiner 3 to the fiber optic collimator 4, and then collimated into a beam by the plano-convex lens 5. The intensity of the incident beam can be adjusted by adjusting the aperture 6. After passing through the beam splitter 7, the beam propagates in two directions, reaching the reference sample 9 and the measurement sample respectively, forming two reflected beams. The two reflected beams pass through the beam splitter again to form a combined beam. After passing through the short focal length plano-convex lens 10, the combined beam is focused and transmitted to the multimode fiber 11 held by the fiber optic holder, and finally collected by the spectrometer 12 and transmitted to the computer 13. The computer 13 processes the collected spectral signal and displays the corresponding differential reflectance spectral signal. Wherein: The light source module includes a stable halogen lamp 1, a stable LED 2, and a fiber optic combiner 3. The halogen lamp 1 is a stable halogen lamp light source with a wavelength range from 360 nm to 2600 nm; the LED 2 is a fiber-coupled LED with a center wavelength of 430 nm; and the fiber optic combiner 3 is a low-loss multimode fiber combiner with an operating wavelength range from 400 nm to 2200 nm. Considering the relatively weak light intensity of the halogen lamp in the 360 ​​nm to 450 nm range, to meet the measurement requirements in the 400 nm to 800 nm visible light band, the LED 2 and the halogen lamp 1 are combined to ensure a suitable light intensity in the 400 nm to 800 nm band.

[0035] The incident optical path module includes a collimator 4, a plano-convex lens 5, an aperture 6, and a beam splitter 7. The collimator 4 uses a fiber coupler with an achromatic lens and is coated with an anti-reflection coating, which can collimate a broadband beam. The plano-convex lens 5 further collimates and narrows the beam. The size of the aperture 6 is adjustable, thereby adjusting the beam diameter and intensity. The beam splitter 7 is a 50:50 Polka dot beam splitter, which can effectively split a broadband light source and reduce the impact of reflected light caused by the anti-reflection coating.

[0036] The reference optical path module includes an optical shutter 8 and a reference sample 9. The optical shutter controls the opening and closing of the reference optical path using the open and closed states of its aperture. When the optical shutter is closed, system dark noise can be measured; when the optical shutter is open, the light intensity signal of the reference optical path can be acquired. The reference sample is a standard sample identical to the blank substrate of the sample to be measured. Its function is to stably reflect the reference light intensity to the reflection optical path module, while ensuring that the light intensity of the reference optical path is approximately equivalent to that of the measurement optical path. The core function of the reference optical path is to provide a reference signal that includes long-term drift fluctuations of the light source. By calculating the intensity ratio of the measurement optical path and the reference optical path, the influence of long-term light source drift on the measurement results can be effectively eliminated.

[0037] The reflected light path module includes a short-focal-length plano-convex lens 10, a multimode fiber 11 held by a fiber optic holder, and a spectrometer 12. The short-focal-length plano-convex lens 10 can focus the reflected light beam over a short distance; by adjusting the position of the multimode fiber 11 held by the fiber optic holder, the focused light beam is collected and incident on the spectrometer 12; the spectrometer 12 has a slit width of 20 µm, 1024 pixels, a wavelength range of 190~980 nm, and an integration time range of 8 ms~60 min.

[0038] The signal processing module is implemented by computer 13, including functions for light intensity threshold judgment, spectral average value calculation, and differential reflectance spectrum calculation. The collimated spot diameter during measurement is 4~5 mm, the spectral measurement range reaches 400~800 nm, and the measurement rate is 10~50 ms / time, which meets the measurement rate requirements.

[0039] Example 2: According to another aspect of the present invention, an asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage is provided, the measurement steps of which are as follows: S1. Start the light source module, turn on the halogen tungsten lamp 1 and LED 2 light sources, power on the spectrometer 12 and connect it to the computer to ensure the system works normally; S2. Adjust the output intensity of LED 2 so that the light intensity at the center wavelength of 430nm is equivalent to the light intensity at 600nm of halogen tungsten lamp 1. S3. Close the optical shutter, allowing the light beam to strike the planetary disk surface but not the sample under test, reducing the dark noise of the acquisition system. ; S4. Adjust the pitch angle of the fiber collimator 4 in the incident light path so that the incident light direction is perpendicular to the measurement sample. Then adjust the position of the multimode fiber 11 held by the fiber holder so that the fiber end face is located at the focal point of the light spot, so that the light intensity of the measurement light path is maximized at this time. S5. Open the light shutter, place the reference sample 9 in the reference light path module and adjust the pitch angle of the reference sample 9 so that the sum of the light intensity of the measurement light path and the reference light path is maximized at this time. S6. Rotate the planetary disk 14. Based on the number of samples and rotation speed of the planetary disk, select the number of wafer samples, the single-wavelength light intensity threshold, the number of sampling points inside the sample wafer, and the number of sampling points outside the sample wafer. The number of wafer samples refers to the total number of samples actually placed. The single-wavelength light intensity threshold is a criterion value used to distinguish whether the light beam is illuminating the sample surface. That is, when the single-wavelength light intensity is less than the light intensity threshold, it is determined that the light beam is not illuminating the sample, and the spectral signal collected by the spectrometer is only the reference light path intensity. When the single-wavelength light intensity is greater than the light intensity threshold, it is determined that the light beam is illuminating the sample, and the spectral signal collected by the spectrometer is the superposition value of the reference light path intensity and the measurement light path intensity. The number of sampling points inside the sample wafer refers to the number of sampling points collected during the measurement process in the area close to the center of the wafer. The number of sampling points outside the sample wafer refers to the number of sampling points collected in the area close to the wafer but where the light beam is not incident on the surface of the wafer. S7. Measurement is performed. The signal processing module first selects the sample to be tested in the planetary disk 14, using the light intensity of a specific wavelength (preferably 600 nm) as a reference. A light intensity threshold is used to distinguish the light intensity signal of the reference optical path from the light intensity signal of the superimposed reference optical path of the measurement optical path. Then, the average spectral intensity of the reference optical path and the measurement optical path is calculated, and the ratio of the two is used to determine the reflectance at each time point of rotation of the sample. Since the sample stage is rotating, the average spectral values ​​of the reference optical path and the measurement optical path correspond to different times in each rotation, thus forming an asynchronous reference mode. The reflectance at the current time is calculated from the reflectance at the initial time and normalized to obtain the differential reflectance spectral value at each time point of rotation. Simultaneously, the light intensity threshold judgment in step S5 can also be used to measure the rotational speed of the MOCVD planetary disk. The specific formula is shown below:

[0040]

[0041] in, For a specific wavelength, For the time corresponding to each rotation, Time shift introduced by rotation, This represents the actual light intensity at the current moment, where the reference optical path and the measurement optical path are superimposed. The actual reference optical path intensity at the current moment. This represents the original light intensity at the current moment, resulting from the superposition of the reference and measurement optical paths. This represents the original reference optical path light intensity corresponding to the previous moment. The system dark noise is measured when the optical shutter is closed, from which the reflectivity at each moment can be calculated:

[0042] in, Given the reflectance at the current moment, the difference between this reflectance and the reflectance at the initial moment is calculated and normalized to obtain the differential reflectance spectral signal for each corresponding moment in each cycle:

[0043]

[0044] in, The differential reflectance spectrum at the current moment. The reflectance is at the initial moment.

[0045] Planetary disk rotation speed The calculation formula is as follows:

[0046] in, and These are the times when the edge of the same sample is measured in the nth and (n-1)th cycles, respectively, which are the times when the single-wavelength light intensity signal corresponding to the same sample reaches the preset light intensity threshold.

[0047] Example 3: (1) Stability measurement In in-situ monitoring of MOCVD thin film deposition, the stability of reflected light intensity is affected by various noises, including light source intensity drift, mechanical vibration disturbance, and thermal radiation. Since the rotation speed of the planetary disk is typically around 20 rpm, the different measurement positions during wafer sample rotation introduce light intensity fluctuations, increasing the measurement error compared to static in-situ measurements. Furthermore, considering the spectrometer's upper limit of 65535 ppm, excessively low light intensity is affected by spectrometer noise, while excessively high intensity may exceed the measurement range during thin film deposition. Therefore, stability tests were conducted on the planetary disk rotation while minimizing the effects of light source intensity fluctuations, mechanical vibration, and intracavity temperature, and adjusting the maximum light intensity to around 40000 ppm.

[0048] Under conditions where the laboratory room temperature remains relatively constant and mechanical vibration is minimized, the light source is turned on and stability measurements are performed. The specific operating steps are as follows: a) Place the planetary disk on the rotating stage and fix it in place, while simultaneously placing the blank sapphire wafer sample on the planetary disk; b) Position the light source perpendicularly onto the wafer sample, adjust the pitch angle of the fiber collimator and the position of the fiber holder to maximize the light intensity, and set the spectrometer integration time to achieve a maximum light intensity of approximately 20,000; c) Open the shutter and adjust the pitch angle of the reference sample to achieve a maximum light intensity of approximately 40,000; d) Set the rotation speed of the planetary disk to 20 rpm. At this point, 20 points can be collected on the wafer sample. The average spectral value of points 8 to 13 is taken as the light intensity of the reference optical path plus the measurement optical path. I 2 After no wafer samples could be collected at all, the average spectral value of the 10th to 20th points was taken as the reference path light intensity. I 1 Each lap yields the reflectance of a specified wafer sample. R e) The reflectance at each moment R t Reflectivity at the initial moment R 0 By subtracting and normalizing, the differential reflectance spectrum value can be obtained.

[0049] In the stability test, the sample remained stationary and no thin film growth was performed. The system stability was evaluated using differential reflectance spectroscopy. The integration time was set to 20 ms, and the average number of trials was 1. First, the optical shutter was closed, allowing the light beam to strike the planetary disk surface without illuminating the sample. Dark noise was collected and subtracted (this step can be completed in advance and reused). Then, the optical shutter was opened, and the planetary disk was rotated. Measurements were continuously taken for 30 minutes, collecting a total of 90,000 sets of spectral data. Based on this, 600 DRS values ​​were calculated, with the DR value variation at 500 nm wavelength as shown below. Figure 2 As shown. Without dark noise subtraction, the variations of 600 DR values ​​at a 500 nm wavelength obtained under the same conditions are as follows: Figure 3 As shown.

[0050] Considering the significant fluctuations in halogen tungsten lamp light source intensity with temperature within 30 minutes of activation, a light source stability comparison experiment was designed to further verify system performance. Under the condition of "sample stationary and not connected to the reference optical path," the integration time, averaging times, and dark noise acquisition method remained consistent with the previous methods. A 30-minute test was conducted, and the DR value variation curve at a wavelength of 500 nm was obtained, as shown below. Figure 4 As shown.

[0051] Experimental results show that, regarding the stability of the light source itself, without preheating, the high-frequency noise fluctuation range of the DR value at 500 nm wavelength is ±0.5%, and the long-term drift within 30 min is about 3%. In the stability test of the differential reflectance spectroscopy system, the high-frequency fluctuation is still ±0.5%, and the long-term drift is reduced to 0.5%. After further subtracting dark noise, the signal fluctuation at 500 nm wavelength can still be controlled within ±0.5%, and there is no long-term drift phenomenon.

[0052] In summary, the high-frequency fluctuation of the DR value of the system of the present invention at a wavelength of 500 nm is stable within ±0.5%, which is close to the high-frequency noise level of the light source itself, and effectively suppresses the influence of long-term drift, which fully demonstrates the high stability and reliability of the system.

[0053] (2) Sample signal measurement In the MOCVD thin film deposition process, the reflectance of the undeposited wafer sample is used as the initial reflectance. Since the measured reflectance is the average value of measurements at a specified point on the sample, this system can characterize the average differential reflectance spectral signal on the surface of the thin film sample. The specific operating steps are as follows: a) Place a blank sapphire substrate and a sample with a 0.65 nm thick, 85.8% coverage submonolayer molybdenum disulfide (MoS2) film in different wafer slots of a planetary disk; b) Adjust the planetary disk rotation speed to 20 rpm, allowing the system to detect the blank sapphire substrate first, denoted as . R 0 When the system detects a MoS2 thin film, it is recorded as... R t c) The reflectivity of MoS2 thin film R t Reflectivity of blank sapphire substrate R 0 By subtracting and normalizing, the differential reflectance spectral value (DRS) can be obtained, such as... Figure 5 As shown, the highest DRS signal value is 0.5, and the waveform is good, indicating that the system has the ability to perform high-precision measurements on sub-monolayer two-dimensional transition metal sulfide films.

[0054] Furthermore, online in-situ monitoring was performed on the MoS2 thin film during MOCVD growth, and differential reflectance spectral data were captured from 20 to 80 minutes into the growth process. DR curves of MoS2 films with different thicknesses and coverage at 500 nm wavelength were obtained, as shown below. Figure 6 As shown in the figure, the curve rises significantly when the MoS2 film begins to deposit and gradually flattens out when deposition stops. These results clearly demonstrate that the system has high sensitivity to MoS2 ultrathin films and can achieve real-time monitoring of their growth process.

[0055] (3) Rotational speed measurement The rotational speed of a planetary disk is typically driven by a mechanical motor and measured using an external encoder. However, this method usually relies on complex hardware and may be susceptible to interference in extreme environments such as high temperatures or vacuum, leading to system instability or the need for frequent maintenance.

[0056] To address this issue, this invention provides a novel method for measuring rotational speed, requiring no external signals or additional hardware support and relying entirely on software to measure the real-time rotational speed of the planetary disk. The system acquires the reflected light intensity signal of the sample using a spectrometer, with an integration time on the order of milliseconds (preferably 8-20 ms). Within this time range, the light intensity reflected by the wafer sample exhibits periodic changes as the planetary disk rotates. By analyzing these light intensity differences, the signal processing module can calculate the real-time rotational speed, thereby achieving high-precision monitoring of the planetary disk.

[0057] This invention measured a planetary disk at a rotational speed of 120° / s, and the results are as follows: Figure 7 As shown. Through analysis and calculation of the periodicity of light intensity, the system can accurately determine the rotational speed of the planetary disk, with a speed error of less than 1° / s, verifying the high precision and reliability of the method. Compared with traditional motor drive and encoder measurement, the speed measurement method of this invention simplifies the system structure and improves the flexibility and adaptability of measurement without adding external hardware.

Claims

1. An asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage, characterized in that, include: The light source module is used to generate a broadband light beam. The light source module includes a halogen tungsten lamp, an LED, and an optical fiber combiner. The two light sources are coupled through the optical fiber combiner to form a broadband light source, ensuring that the light source intensity in the 400 nm to 800 nm band is appropriate. The incident light path module is used to collimate the above-mentioned light beam to the sample surface inside the MOCVD cavity; The reference optical path module is used to calibrate the intensity of the beam emitted by the light source; The reflected light path module is used to converge and transmit the reflected light from the measurement light path and the reflected light from the reference light path to the spectral detection component; The signal processing module is used to determine the light intensity threshold, calculate the average spectral value, and calculate the differential reflectance spectrum.

2. The asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage according to claim 1, characterized in that, The incident optical path module includes a collimator, a plano-convex lens, an aperture, and a beam splitter. The collimator is used to transform the diverging beam emitted from the optical fiber into an approximately collimated beam. The plano-convex lens is used to improve the collimation of the beam. The aperture is used to adjust the beam size. The beam splitter is used to reflect the incident beam to the reference optical path, transmit it to the sample surface inside the MOCVD cavity to form the measurement optical path, and reflect and transmit the beams reflected by the sample and the reference sample inside the cavity into the reflection optical path module, respectively.

3. The asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage according to claim 1, characterized in that, The reference optical path module includes an optical shutter and a reference sample; the optical shutter is used to control the opening and closing of the reference optical path. When the optical shutter is closed, the dark noise of the system is measured; when the optical shutter is open, the light intensity signal of the reference path is measured; the reference sample is the same as the blank substrate and is used to reflect the reference light intensity into the reflection optical path module.

4. The asynchronous reference differential reflectance spectroscopy system for an MOCVD rotating sample stage according to claim 1, characterized in that, The reflected optical path module includes a short focal length plano-convex lens, a multimode fiber held by a fiber optic holder, and a spectrometer. The short focal length plano-convex lens is used to converge the reflected beam; the multimode fiber held by the fiber optic holder collects the converged beam and incident it into the spectrometer.

5. An asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage, implemented based on the system described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Start the light source module, close the light shutter, so that the light beam is incident on the surface of the planetary disk but does not illuminate the sample to be tested, and collect the dark noise of the system; S2. Adjust the incident light path to maximize the intensity of the received reflected light; S3. Open the optical shutter, place the reference sample in the reference optical path module and adjust it to maximize the intensity of the received reflected light; S4. Based on the rotational speed of the planetary disk, determine the number of samples, the light intensity threshold, the number of points required inside the sample to be tested, and the number of points required outside the sample. S5. Perform measurements and use the signal processing module to solve the spectral data of the sample to be tested in the rotating planetary disk: distinguish the reference light and the measurement light signal by the light intensity threshold, calculate the real-time reflectance, and calculate the differential reflectance spectrum based on the initial reflectance.

6. The asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage according to claim 5, characterized in that, The solution performed by the signal processing module in step S5 includes: Using the light intensity of a specific wavelength as a reference, the light intensity of the reference optical path is distinguished from the light intensity of the superimposed reference optical path of the measurement optical path by using a light intensity threshold. After calculating the average spectral intensity of the reference optical path and the measurement optical path, the reflectance of the sample under test at each time point after one rotation is determined by the ratio of the two values. Since the sample stage is rotating, the average spectral values ​​of the reference optical path and the measurement optical path correspond to different times in each revolution, thus forming an asynchronous reference mode; The difference between the reflectance at the current moment and the reflectance at the initial moment is calculated and normalized to obtain the differential reflectance spectral value for each corresponding moment of each cycle. The specific formula is as follows: in, For a specific wavelength, For the time corresponding to each rotation, Time shift introduced by rotation, This represents the actual light intensity at the current moment, where the reference optical path and the measurement optical path are superimposed. The actual reference optical path intensity at the current moment. This represents the original light intensity at the current moment, resulting from the superposition of the reference and measurement optical paths. The light intensity of the original reference optical path at the current moment. The system dark noise is measured when the optical shutter is closed, and the reflectivity at each current moment is calculated from this: in, Given the reflectance at the current moment, the difference between this reflectance and the reflectance at the initial moment is calculated and normalized to obtain the differential reflectance spectral signal for each corresponding moment of each cycle: in, The differential reflectance spectrum at the current moment. The reflectance is at the initial moment.

7. The asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage according to claim 6, characterized in that, The specific wavelength is 600nm.

8. The asynchronous reference differential reflectance spectroscopy measurement method for an MOCVD rotating sample stage according to claim 5, characterized in that, The asynchronous reference differential reflectance spectroscopy measurement method for MOCVD rotating sample stages, wherein the planetary disk rotation speed is... The calculation formula is as follows: in, and These are the times when the edge of the same sample is measured in the nth and (n-1)th cycles, respectively, which are the times when the single-wavelength light intensity signal corresponding to the same sample reaches the preset light intensity threshold.

Images