Temperature oscillation growth method for improving uniformity of GaAs epitaxial layer

Abstract

The invention belongs to the technical field of semiconductor manufacturing, and particularly relates to a temperature oscillation growth method for improving the uniformity of a GaAs epitaxial layer, which comprises the following steps of: placing a GaAs substrate in an MOCVD (Metal Organic Chemical Vapor Deposition) reaction chamber to carry out hydrogen atmosphere thermal cleaning; setting process parameters such as target growth temperature, gas flow and reaction chamber pressure; setting the amplitude and period of periodic oscillation around the target growth temperature; iII-group and V-group source gases are synchronously introduced, and a temperature oscillation program is started, so that the temperature of the substrate is periodically oscillated according to set parameters, and epitaxial growth is carried out; continuously oscillating and growing to a target thickness; and stopping the III-group source, and cooling under the protection of the V-group source. The growth interface is actively disturbed through temperature oscillation, so that the growth tends to a two-dimensional layered mode, and the macroscopic thickness and component uniformity of the epitaxial layer are improved. Periodic temperature change is equivalent to in-situ annealing, dislocation density is reduced, and crystal quality is improved. And the method has universality on epitaxial growth of various III-V group compounds such as GaAs, AlGaAs, InGaAs and the like.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, specifically relating to a temperature oscillation growth method for improving the uniformity of GaAs epitaxial layers. Background Technology

[0002] Gallium arsenide (GaAs), as a representative of second-generation semiconductor materials, is widely used in lasers, high-frequency microwave devices, light-emitting diodes and solar cells due to its high electron mobility, direct bandgap and excellent optoelectronic properties.

[0003] In GaAs epitaxial growth, especially on large-size (e.g., 4-inch, 6-inch) substrates, obtaining a highly uniform epitaxial layer is key to ensuring consistent device performance and improving production yield.

[0004] However, the MOCVD growth technology uses a constant temperature mode, and there are subtle differences in temperature, airflow, and source concentration in the local microenvironment of the growth interface. The adsorbed atoms have insufficient kinetic energy and uneven migration ability, which can easily lead to local over- or under-accumulation. This results in fluctuations in epitaxial layer thickness and uneven composition, which manifests as significant differences in performance in different areas of the substrate, failing to meet the requirements for high-precision device fabrication.

[0005] The accumulation of crystal defects in related technologies is difficult to avoid. During constant-temperature growth, rapid atomic deposition easily leads to structural hazards such as microscopic defects and dislocations, and there is a lack of active repair mechanisms. These defects accumulate continuously with the increase of epitaxial layer thickness, reducing crystal integrity. The presence of defects directly affects the conductivity and optical performance of the epitaxial layer, resulting in shortened lifespan and performance degradation of devices fabricated based on it, limiting the application scenarios of high-end devices. Moreover, if the source gas introduction and temperature control are not synchronized during the process, and there is no targeted atmosphere protection during the cooling process after growth, it is easy to cause atomic desorption and oxidation on the epitaxial layer surface, or thermal stress cracks due to sudden temperature changes, deteriorating product quality. Summary of the Invention

[0006] This invention provides a temperature oscillation growth method for improving the uniformity of GaAs epitaxial layers. This invention embeds an oscillation curve into the temperature control program of the MOCVD equipment, requiring no modification to the reaction chamber, gas path, or other hardware. Temperature oscillation can reduce the defect density of the epitaxial layer by mitigating microscopic defects and dislocations generated during the growth process.

[0007] The methods include: S1: Prepare a gallium arsenide substrate and place the gallium arsenide substrate in the reaction chamber of the MOCVD equipment; S2: Under a hydrogen atmosphere, the temperature of the gallium arsenide substrate is raised to a first preset temperature and kept at that temperature to perform thermal cleaning on the substrate surface. S3: Set the target process parameters for epitaxial growth, including: target growth temperature, group III source gas flow rate, group V source gas flow rate, and reaction chamber pressure; S4: Set the execution parameters for the temperature oscillation program, including the amplitude and period of the periodic oscillation around the target growth temperature; S5: Introduce the group III source gas and the group V source gas into the reaction chamber, and simultaneously start the temperature oscillation program so that the substrate temperature oscillates periodically around the target growth temperature set in S3 according to the amplitude and period set in S4, and the epitaxial layer growth begins. S6: Under the control of the temperature oscillation program, epitaxial growth continues until the epitaxial layer thickness reaches the preset value; S7: Stop the flow of the group III source gas and cool the substrate in a group V source gas atmosphere.

[0008] It should be further noted that in S2, raising the substrate temperature to the first preset temperature and maintaining it in a hydrogen atmosphere specifically includes the following steps: S21: Replace the atmosphere in the reaction chamber with a pure hydrogen gas flow, and raise the substrate temperature from room temperature to a processing temperature between 650°C and 800°C at a heating rate of 10°C / second to 30°C / second. S22: Under a pure hydrogen atmosphere, the gallium arsenide substrate is maintained at the processing temperature, and the reaction chamber pressure is controlled within the range of 50 mbar to 200 mbar for 5 to 20 minutes. S23: After completing the continuous processing of S22, the substrate temperature is reduced from the processing temperature to the target growth temperature, which is lower than the processing temperature and within the range of 600°C to 750°C. S24: After the substrate temperature stabilizes at the target growth temperature, the gas environment in the reaction chamber is switched from a pure hydrogen atmosphere to a hydrogen carrier gas mixture containing group V source process gases, and the reaction chamber pressure is stabilized to the set value required for growth.

[0009] It should be further noted that in S5, the process of introducing the Group III source gas and the Group V source gas into the reaction chamber and simultaneously initiating a temperature oscillation program to ensure that the substrate temperature follows the amplitude and period set in S4 specifically includes the following steps: S51: Confirm that the airflow, pressure and substrate temperature in the reaction chamber have stabilized at the target process parameters set in S3, and enter the preparation state; S52: Control the gas flow path switching, introduce V-type source gas from the flow rate set by S3 into the reaction chamber, and maintain this flow. S53: After introducing the Group V source gas, wait for a preset delay time, and then open the Group III source gas flow path from the flow rate set in S3. S54: At the same time as opening the Group III source gas flow path or within 1-3 seconds thereafter, send a start command to the temperature controller of the MOCVD equipment to trigger the execution of the temperature oscillation program set in S4. S55: After the temperature oscillation program is started, the temperature sensor data monitored in real time confirms that the substrate temperature has entered a periodic oscillation trajectory based on the target growth temperature set in S3. At this time, epitaxial layer growth begins.

[0010] It should be further explained that in S5, the periodic oscillation around the target growth temperature set in S3 to begin epitaxial layer growth specifically includes the following steps: S511: Introduce high-purity Group V source gas into the MOCVD reaction chamber to replace residual hydrogen in the chamber and maintain the preset atmosphere parameters; S512: Start the group III source gas in a gradient-increment manner, adjust the flow rate to the target value set in S3 and monitor pipeline stability; S513: After the group III source flow rate stabilizes, start the temperature oscillation program to make the substrate temperature oscillate around the target growth temperature set in S3 according to the parameters in S4.

[0011] It should be further explained that in S6, under the control of the temperature oscillation program, epitaxial growth continues until the epitaxial layer thickness reaches the preset value. Specifically, this includes the following steps: S61: Under the conditions of temperature oscillation and continuous flow of reaction gas, monitor and adjust the pressure and flow rate of reaction chamber in real time to stabilize them within the target process parameter range set in S3. S62: Collect real-time temperature data of the gallium arsenide substrate and compare it with the target curve of the temperature oscillation program set in S4 to ensure that the amplitude, period and center temperature value of the actual temperature oscillation are maintained within the preset tolerance band. S63: Using an in-situ optical monitoring device, the optical signal of the growth surface is acquired in real time, and the characteristics of the optical signal are used to determine whether the epitaxial layer is in a continuous two-dimensional layered growth mode. S64: Based on the preset target thickness of the epitaxial layer, the growth process ends when the target thickness is reached, through growth time timing control or in-situ film thickness monitoring signal.

[0012] It should be further noted that, in S7, cooling the substrate under the Group V source gas atmosphere specifically includes the following steps: S71: When the epitaxial layer thickness reaches the preset value, the supply of group III source gas is turned off, and an oscillation decay-surface stabilization process is started to drive the substrate temperature to continue to perform 2 to 5 complete temperature oscillation cycles with half the amplitude in the group V source atmosphere. S72: After completing the oscillation cycle, control the substrate temperature in the V-group source atmosphere, starting from the current temperature, first reduce it to an intermediate temperature point at a first cooling rate and hold it briefly, then reduce it to a lower preparation temperature at a second cooling rate lower than the first cooling rate. S73: At the preparation temperature, shut off the V-source gas supply, switch to a pure hydrogen or inert gas atmosphere, and cool the substrate to a temperature at which it can be safely removed at the third cooling rate.

[0013] It should be further noted that the following steps are included after S2: S211: Under a hydrogen atmosphere, the temperature of the thermally cleaned substrate is reduced from a first preset temperature to a second preset temperature and maintained at the second preset temperature for a period of time; S212: At the second preset temperature, introduce a group V source gas into the reaction chamber and establish a stable partial pressure, but do not introduce a group III source gas, and maintain the state for 1 to 5 minutes. S213: The substrate temperature is increased from the second preset temperature to the third preset temperature at a controllable rate, wherein the third preset temperature is lower than the target growth temperature T0 set in S3; S214: At the third preset temperature, a group III source gas and a group V source gas are simultaneously introduced to grow an initial buffer layer with a thickness of 10 to 50 nanometers at a constant temperature. S215: Turn off the group III source gas, and in the group V source gas atmosphere, raise the substrate temperature from the third preset temperature at a preset rate to the target growth temperature T0 set in S3, and stabilize it for 1 to 3 minutes after reaching T0.

[0014] It should be further noted that the following steps are also included between S5 and S6: S611: After the temperature oscillation program is started and runs stably for 5 to 10 complete cycles, the in-situ optical thickness monitoring system is started. Based on the oscillation frequency of the monitored reflection signal, the transient growth rate is deduced and recorded in real time. S612: Compare the continuously recorded transient growth rate with a theoretical average growth rate pre-calculated based on process parameters. If the average measured rate of multiple consecutive cycles deviates from the theoretical value by more than ±3%, then adjust the mass flow rate setting of the Group III source gas proportionally, with the adjustment range not exceeding ±5% of the original setting. S613: When the epitaxial layer thickness is confirmed to reach about one-third of the preset total thickness through time integration or in-situ monitoring, while maintaining temperature oscillation, the flow rate of the group V source gas is temporarily increased by 20% to 40% on the original basis, and this high flow rate is maintained for 2 to 5 complete temperature oscillation cycles, after which the original flow rate is restored. S614: When the thickness of the epitaxial layer reaches about two-thirds of the preset total thickness, a correction instruction is embedded in the temperature control program so that the starting point of the cooling stage of each temperature oscillation cycle is changed from a fixed T0+ amplitude value to a value dynamically determined based on the actual temperature peak of the previous cycle, with the value fluctuating within the range of -2℃ to +1℃ of the previous peak temperature. S615: When the growth process enters the final stage and the estimated thickness reaches 85% to 90% of the target thickness, an oscillation convergence subroutine is started. The oscillation convergence subroutine controls the amplitude of the temperature oscillation to decrease linearly by 5% to 10% in each subsequent cycle until the amplitude decays to less than 20% of the initial value. Then, the continuous growth in S6 continues until the final thickness is reached.

[0015] It should be further noted that the following steps are included after S6: S621: At a predetermined time or when the epitaxial layer thickness is less than a preset value, the amplitude of the temperature oscillation program is gradually reduced. S622: After the amplitude decreases to zero or a preset minimum value, maintain the substrate temperature at the target growth temperature set in S3, and continue to supply group III source gas and group V source gas for a predetermined time. S623: After completing the continuous inlet of S622, the flow rate of the group III source gas is linearly reduced to zero within 2 to 5 seconds, and then S7 is executed.

[0016] It should be further noted that the method is applicable to the growth of gallium arsenide materials, aluminum gallium arsenide, or indium gallium arsenide epitaxial layers.

[0017] As can be seen from the above technical solutions, the present invention has the following advantages: The temperature oscillation growth method provided by this invention for improving the uniformity of GaAs epitaxial layers improves the uniformity of epitaxial layers. Temperature oscillation provides periodic kinetic energy replenishment for adsorbed atoms. The heating stage enhances the atomic migration ability and enables them to occupy lattice positions. The cooling stage suppresses excessive adsorption, buffers the growth rate, and breaks the influence of local microenvironment differences, thereby achieving uniform two-dimensional layered growth of epitaxial layers. The thickness deviation of different regions of the substrate is controlled within a controllable range.

[0018] This invention effectively reduces crystal defect density, and the periodic temperature change forms an annealing-like effect, which repairs micro-defects and dislocations generated during the growth process, reduces defect accumulation, improves crystal integrity, ensures the stability of the electrical and optical properties of the epitaxial layer, and extends the service life of downstream devices.

[0019] This invention can be applied to the growth of various III-V compounds without requiring a reconfiguration of the process system; it reduces the impact of environmental fluctuations on product quality and ensures product consistency across different batches and equipment. This invention improves process continuity stability, with atmosphere control, temperature regulation, and source supply designed synchronously at each stage, ensuring structural stability of the epitaxial layer from growth to cooling, and achieving the required surface quality. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart of a temperature-oscillating growth method for improving the uniformity of GaAs epitaxial layers. Figure 2 This is a schematic diagram of a temperature oscillation growth curve; Figure 3 A comparison of epitaxial wafer thickness distribution after conventional isothermal growth and temperature oscillation growth; Figure 4 3D morphology of wafer surface under conventional isothermal growth; Figure 5 This is a 3D morphology image of the wafer surface under temperature oscillation growth. Detailed Implementation

[0022] The temperature oscillation growth method for improving the uniformity of GaAs epitaxial layers provided by this invention controls the substrate temperature to oscillate continuously and periodically around a preset target growth temperature during gallium arsenide epitaxial growth in an MOCVD device. This invention allows for periodic temperature changes, which is equivalent to applying an active and flexible "perturbation" to the growth interface.

[0023] During the heating phase, atoms adsorbed on the growth surface gain additional kinetic energy, enhancing their migration ability and making it easier for them to find the lowest-energy lattice sites. During the cooling phase, excessive atomic adsorption is suppressed, and the growth rate is temporarily buffered. This periodic "promotion-buffering" cycle effectively breaks the continuous non-uniform growth trend caused by differences in local microenvironments, forcing the epitaxial layer to grow in a more two-dimensional layered pattern, thereby achieving uniform growth.

[0024] The following describes in detail the temperature oscillation growth method for improving the uniformity of GaAs epitaxial layers according to this application. Specific details, such as particular system structures and techniques, are presented for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application can also be implemented in other embodiments without these specific details.

[0025] It should be understood that, when used in this specification, the term "comprising" indicates the presence of the described feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0026] The terms "one embodiment" or "some embodiments" used in this application mean that one or more embodiments of this application include the specific features, structures, or characteristics described in that embodiment. Therefore, the phrases "in one embodiment," "in one embodiment," "in some other embodiments," "in other embodiments," etc., appearing in different parts of this application do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0027] 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.

[0028] Please see Figure 1 The diagram shows a flowchart of a temperature-oscillating growth method for improving the uniformity of GaAs epitaxial layers in a specific embodiment. The method includes: S1: Configure a gallium arsenide substrate and place the gallium arsenide substrate in the reaction chamber of the MOCVD equipment.

[0029] In one embodiment, a gallium arsenide single-crystal substrate based on crystal orientation is used. Before being placed in the reaction chamber, the substrate undergoes organic solvent degreasing, acidic solution etching to remove the mechanically damaged layer, and dilute hydrochloric acid solution to remove the native oxide. Finally, it is dried with high-purity dehydrating nitrogen gas.

[0030] Furthermore, during loading, a polished graphite or silicon carbide substrate is used to precisely place the substrate in the hot zone of the substrate, ensuring good contact between the back of the substrate and the substrate to guarantee heat conduction.

[0031] S2: Under a hydrogen atmosphere, the temperature of the substrate is raised to a first preset temperature and kept at that temperature to perform thermal cleaning on the substrate surface.

[0032] In one embodiment, under high-temperature conditions, hydrogen molecules undergo catalytic dissociation on a clean GaAs surface, generating active hydrogen atoms (H*). These active hydrogen atoms react with arsenic oxides (such as As₂O₃) and gallium oxides (such as Ga₂O₃) on the substrate surface to generate volatile AsH₃ and H₂O, with the H₂O being carried away by a high-speed gas flow. Adsorbed hydrocarbons are pyrolyzed and hydrogenated, generating gaseous products such as CH₄, which are then removed. Stable temperature and pressure ensure the uniformity of the chemical reaction rate and contaminant desorption rate.

[0033] In some specific embodiments, S2 specifically includes the following steps: S21: Replace the atmosphere in the reaction chamber with a pure hydrogen gas flow, and raise the substrate temperature from room temperature to a processing temperature between 650°C and 800°C at a heating rate of 10°C / second to 30°C / second.

[0034] In one embodiment, the rapid heating process reduces the time the substrate spends in the intermediate temperature region, thereby reducing the likelihood that certain contaminants will react with the substrate in a solid state or form stable compounds at intermediate temperatures.

[0035] Furthermore, the temperature is increased in a hydrogen atmosphere, where the hydrogen begins to preheat and prepares for the subsequent high-temperature reduction reaction. The set heating rate range is determined based on the thermal conductivity and thermal expansion characteristics of III-V compound semiconductor materials such as GaAs, which can balance the process cycle time with the risk of thermally induced defects.

[0036] S22: Under a pure hydrogen atmosphere, maintain the gallium arsenide substrate at the processing temperature, control the reaction chamber pressure within the range of 50 mbar to 200 mbar, and continue processing for 5 to 20 minutes.

[0037] In one embodiment, under high temperature and hydrogen atmosphere, arsenic oxide (such as As2O3) and gallium oxide on the substrate surface undergo a reduction reaction with hydrogen atoms to generate gaseous arsine (AsH3) and water vapor (H2O), which are then carried away by the gas flow.

[0038] Furthermore, the adsorbed hydrocarbons and other organic matter undergo thermal decomposition and hydrogenation reactions, generating small molecule gases such as methane which are then removed. Precise control of the treatment pressure can regulate the residence time of hydrogen on the surface and the reaction rate; too low a pressure may result in incomplete cleaning, while too high a pressure may inhibit the desorption of the products. The treatment time ensures that contaminants at all points on the surface have sufficient time to react and desorb.

[0039] S23: After completing the continuous processing of S22, the substrate temperature is reduced from the processing temperature to the target growth temperature, which is lower than the processing temperature and within the range of 600°C to 750°C.

[0040] In one embodiment, after high-temperature cleaning, the heater is controlled to allow the substrate temperature to drop smoothly from a higher processing temperature to a pre-planned target epitaxial growth temperature.

[0041] The cooling process typically employs a controllable cooling rate, such as 5°C / second to 15°C / second, to ensure the uniformity and controllability of temperature changes.

[0042] Furthermore, the target growth temperature is lower than the processing temperature, which is the optimal temperature for the epitaxial growth of thin film materials after optimization. At this temperature, processes such as precursor decomposition, surface migration, and lattice embedding can achieve the desired kinetic equilibrium.

[0043] S24: After the substrate temperature stabilizes at the target growth temperature, the gas environment in the reaction chamber is switched from a pure hydrogen atmosphere to a hydrogen carrier gas mixture containing group V source process gases, and the reaction chamber pressure is stabilized to the set value required for growth.

[0044] In one embodiment, a group V source gas is introduced into the system at the target growth temperature to pre-form a stable surface reconstruction rich in group V elements on the clean III-V substrate surface before growth begins.

[0045] For example, when AsH3 is introduced into a GaAs substrate, arsenic atoms adsorb onto the surface, forming a specific arsenic-stabilized surface structure. This prevents the substrate from decomposing due to arsenic volatilization at high temperatures and provides a suitable atomic arrangement template for the upcoming deposition of group III atoms.

[0046] Maintaining stable reaction chamber pressure ensures constant partial pressure and residence time of precursor gases, which are important parameters for controlling growth rate and material composition uniformity.

[0047] S3: Set the target process parameters for epitaxial growth, including: target growth temperature, group III source gas flow rate, group V source gas flow rate, and reaction chamber pressure.

[0048] In one embodiment, the MOCVD equipment, short for Metal-Organic Chemical Vapor Deposition, is a key process equipment for depositing semiconductor thin films on substrate surfaces through vapor-phase chemical reactions. The MOCVD equipment control system uses a human-machine interface to preset recipes. The target growth temperature is precisely set within the range of 600-750°C based on the GaAs, AlGaAs, target doping concentration, and mobility. For example, at 700°C. The flow rates of the Group III and Group V sources are determined by the setpoints of a mass flow controller to achieve a specific molar flow ratio. The reaction chamber pressure is set to a stable value between 50 and 200 mbar through coordinated regulation of the upstream total inlet flow rate and the downstream electric throttle valve. The reaction chamber pressure controls the mean free path and residence time of gas molecules, thereby affecting gas phase transport and reaction kinetics. These parameters collectively constitute the gas phase environment baseline for epitaxial growth.

[0049] S4: Set the execution parameters for the temperature oscillation program, the execution parameters including the amplitude and period of the periodic oscillation around the target growth temperature.

[0050] In one embodiment, a periodic waveform function is defined in the interface of the temperature controller, with the target growth temperature T set by S3 as the center baseline. The amplitude is set between ±10°C and ±20°C, for example, ±15°C, meaning that the temperature will vary between T0-ΔT and T0+ΔT.

[0051] The period is set between 30 and 120 seconds, such as 60 seconds, defining the time required for one complete oscillation. The waveform is typically a linearly varying triangular or sine wave, with specified rise and fall times. The period determines the perturbation frequency and needs to match the characteristic timescales of surface atomic diffusion, nucleation, and step progression. The choice of waveform affects the rate of temperature change, thus influencing the system's dynamic response.

[0052] S5: Introduce the group III source gas and the group V source gas into the reaction chamber, and simultaneously start the temperature oscillation program so that the temperature of the substrate oscillates periodically around the target growth temperature set in S3 according to the amplitude and period set in S4, and the epitaxial layer growth begins.

[0053] In one embodiment, after confirming that the temperature, pressure, and flow rate have stabilized at the S3 setpoint, the gas path of the group V source (AsH3) is opened and its flow rate is stabilized. Within a preset time interval, two parallel operations are performed: first, the gas path of the group III source TMGa is opened, allowing group III atoms to begin being transported to the growth interface.

[0054] Second, a start command is sent to the temperature controller to activate the temperature oscillation waveform pre-programmed in S4. The controller then dynamically adjusts the heater power based on the waveform function and real-time temperature feedback, driving the substrate temperature to begin periodic changes.

[0055] S6: Under the control of the temperature oscillation program, epitaxial growth continues until the epitaxial layer thickness reaches the preset value.

[0056] In one embodiment, the conditions at the growth interface change periodically during continuous temperature oscillations, but the average growth rate remains essentially constant within one cycle. Therefore, the total thickness is the product of the average growth rate and the total growth time. The in-situ laser reflectometer utilizes the principle of optical interference, and its signal is extremely sensitive to changes in the optical thickness of the growth surface. Because the temperature oscillation period is much shorter than the time required to grow one optical thickness cycle, the envelope of the interference fringes remains smooth, which can be used to accurately determine the total thickness.

[0057] In some specific embodiments, S6 specifically includes the following steps: S61: Under the conditions of temperature oscillation and continuous flow of reaction gas, monitor and adjust the pressure and flow rate of the reaction chamber in real time to stabilize them within the target process parameter range set in S3.

[0058] In one embodiment, pressure data within the reaction chamber is collected using a capacitive diaphragm gauge or an ionization gauge on the chamber. This pressure data is transmitted to a pressure controller and compared with the target pressure value set in step S3. If a pressure deviation exceeding a preset threshold is detected, a signal is sent to an electric throttle valve located on the reaction chamber's exhaust pipe to fine-tune the valve opening or the total intake flow rate, allowing the pressure to quickly return to the set point.

[0059] Furthermore, the mass flow controller performs closed-loop control of the airflow from Group III sources (such as TMGa) and Group V sources (such as AsH3). The thermal or differential pressure sensor inside the MFC continuously measures the actual flow rate and compares it with the set value. By adjusting the opening of its internal proportional valve, the flow rate fluctuation is controlled within ±0.5% of the set value.

[0060] Furthermore, for the V / III ratio, the system achieves this by locking the set flow rates of the two source gases separately, without performing linked proportional adjustments; however, its stability is a natural result of the stability of their respective flow rates. This process operates continuously throughout the entire growth process.

[0061] Furthermore, the stability of the reactant gas flow rate directly determines the atomic flux delivered to the growth surface, and is a major factor controlling the growth rate, material composition, and doping concentration. Under high-frequency temperature oscillations, the surface reaction rate is already in a dynamic state. If the gaseous precursor supply also fluctuates, the coupling between the two will produce unpredictable and complex effects, disrupting the stability and repeatability of the process. Maintaining statically stable pressure and flow rate under dynamic temperature conditions, limiting the disturbance to the temperature dimension, is a prerequisite for analyzing the effect of a single variable like temperature oscillation.

[0062] S62: Collect real-time temperature data of the gallium arsenide substrate and compare it with the target curve of the temperature oscillation program set in S4 to ensure that the amplitude, period and center temperature value of the actual temperature oscillation are maintained within the preset tolerance band.

[0063] In one embodiment, during the growth process, thermocouples mounted on the bottom or side of the substrate are aligned with an infrared pyrometer on the back of the substrate to continuously collect temperature data. This real-time temperature data is sent to a monitoring system. The system extracts the amplitude, period, and average temperature of the current oscillation cycle from these data streams in real time.

[0064] Furthermore, the extracted actual amplitude, period, and average temperature values ​​are compared in real time with the target amplitude, target period set in S4, and target growth temperature set in S3.

[0065] Furthermore, a preset allowable tolerance range is established, such as amplitude deviation ±1℃, period deviation ±2 seconds, and center temperature deviation ±1℃. As long as the real-time data falls within this tolerance range, the oscillation is considered normal. If it continues for a certain period of time or the deviation exceeds the threshold, the monitoring system can issue an alarm to prompt operator intervention.

[0066] S63: Using an in-situ optical monitoring device, the optical signal of the growth surface is acquired in real time, and the characteristics of the optical signal are used to determine whether the epitaxial layer is in a continuous two-dimensional layered growth mode.

[0067] In one embodiment, the principle of the laser reflectometer is based on optical thin-film interference. When light is reflected at the interface of media with different refractive indices, the intensity of the reflected light depends on the phase difference between the reflected beams, which is directly related to the optical thickness n*d of the thin film, the refractive index multiplied by the physical thickness.

[0068] Furthermore, during the growth process, the epitaxial layer thickness d continuously increases, causing the reflected light intensity to exhibit periodic changes. Each complete interference cycle corresponds to an increase in optical thickness of λ / (2n), where λ is the wavelength of the laser in vacuum.

[0069] Smooth, regular interference fringes indicate a smooth growth surface and a uniform increase in thickness, which are typical characteristics of two-dimensional layered growth.

[0070] If the surface roughness increases, the incident light will undergo diffuse reflection, which will weaken the interference signal collected in the direction of specular reflection, reduce the contrast of the fringes, and even make them become disordered.

[0071] Therefore, this optical signal is a sensitive probe of surface morphology and growth pattern.

[0072] In temperature oscillation growth, stable interference fringes are expected, which proves that the growth pattern tends to be two-dimensional layered.

[0073] S64: Based on the preset target thickness of the epitaxial layer, the growth process ends when the target thickness is reached, through growth time timing control or in-situ film thickness monitoring signal.

[0074] In one embodiment, time-based endpoint control is possible: after setting the target growth temperature, reactant gas flow rate, and pressure in S3, the material growth rate under specific conditions is essentially fixed. The system calculates the required total growth time based on the target thickness and the known growth rate.

[0075] The timer starts the instant step S5 begins. When the timer reaches the preset total growth time, the system automatically triggers the instruction for step S7.

[0076] Furthermore, endpoint control can be based on in-situ measurements: using the laser reflectometer described in step S63, the number of cycles of the reflected light intensity oscillation can be analyzed in real time. Each complete interference cycle corresponds to a fixed optical thickness increment Δ(n*d)=λ / 2. By accumulating the number of interference cycles, the cumulative optical thickness of the epitaxial layer can be calculated.

[0077] When the accumulated thickness reaches the preset target optical thickness, the system sends a signal to stop growth. This in-situ signal-based method is more accurate when growing complex or multilayer structures.

[0078] In one embodiment of the present invention, the following steps are included after S6: S621: Before the epitaxial layer thickness reaches a preset value, at a predetermined time or when the predetermined thickness is reached, the amplitude of the temperature oscillation program is gradually reduced.

[0079] S622: After the amplitude decreases to zero or a preset minimum value, maintain the substrate temperature at the target growth temperature set in S3, and continue to introduce the group III source and group V source gases for a predetermined time.

[0080] S623: After completing the continuous inlet of S622, the flow rate of the group III source gas is linearly reduced to zero within 2 to 5 seconds, and then S7 is executed.

[0081] S7: Stop the flow of the group III source gas and cool the substrate under the atmosphere of the group V source gas.

[0082] In some specific embodiments, S7 specifically includes the following steps: S71: When the epitaxial layer thickness reaches the preset value, the supply of group III source gas is turned off, and an oscillation decay-surface stabilization process is started to drive the substrate temperature to continue to perform 2 to 5 complete temperature oscillation cycles with half the amplitude in the group V source atmosphere.

[0083] In one embodiment, after the film thickness monitoring system or growth time controller determines that the epitaxial layer has reached the target thickness, the control system performs the first action: sending a shutdown command to the mass flow controller of the group III source (such as TMGa) to cut off its supply to the reaction chamber. Hydrogen carrier gas continues to flow to purge the pipeline.

[0084] Simultaneously, a second action is triggered: the temperature control program calls a subroutine. The subroutine instructs the heater to immediately reduce the amplitude setpoint to half of its original value, instead of oscillating at the full amplitude of the growth stage, while maintaining the oscillation period. At this halved amplitude, the substrate temperature continues to oscillate completely around the original target growth temperature T0 for 2 to 5 cycles. During these cycles, the flow rate of the group V source remains exactly the same as during the growth stage. This stabilizes the surface at the ideal arsenic termination and reconstruction state.

[0085] S72: After completing the oscillation cycle, control the substrate temperature in the V-group source atmosphere, starting from the current temperature, first reduce it to an intermediate temperature point at a first cooling rate and hold it briefly, then reduce it to a lower preparation temperature at a second cooling rate lower than the first cooling rate.

[0086] In one embodiment, the temperature control system then switches to a two-step cooling mode.

[0087] The first step is to control the heater power so that the substrate temperature drops at a relatively fast rate, for example, 30°C to 50°C per minute, from the temperature at the end of the oscillation, close to T0, to an intermediate temperature point.

[0088] This intermediate temperature point is set between 550°C and 650°C, for example, 600°C.

[0089] Furthermore, once the temperature reaches this point, the system maintains this temperature for a short period of time, such as 1 to 3 minutes, while maintaining the V-source airflow.

[0090] After the second heat treatment step is completed, the second cooling step begins. This time, the cooling rate is adjusted to a slower rate than the first step, such as 15°C to 25°C per minute, lowering the substrate temperature from the intermediate temperature point to a lower preparation temperature, typically set between 400°C and 500°C. Throughout the two-step cooling process, the group V source gas is continuously supplied. Reducing the residual thermal stress generated within the crystal due to the temperature gradient is crucial for lowering the dislocation density and warpage of the epitaxial layer.

[0091] S73: At the preparation temperature, shut off the V-source gas supply, switch to a pure hydrogen or inert gas atmosphere, and cool the substrate to a temperature at which it can be safely removed at the third cooling rate.

[0092] In one embodiment, the group V source is shut down at 450°C because at this temperature, the desorption rate of arsenic atoms on the gallium arsenide surface is already very low, and the surface structure is relatively stable. Shutting down the group V source at this time avoids the instantaneous loss of surface arsenic that might occur if it were shut down at higher temperatures.

[0093] The immediate switch to an inert atmosphere is to replace and purge the residual Group V source gas and its decomposition products in the reaction chamber with a chemically inert gas, preventing particulate contamination from condensing on the cooler reaction chamber walls or components during subsequent cooling. The final third cooling rate is carried out in a chemically inert environment at a relatively low temperature. The main consideration is to allow the heat from the substrate and its supporting base to dissipate in a near-equilibrium manner, eliminating any minor temperature unevenness that may occur in the final stage, and ensuring that the wafer does not develop imperceptible micro-deformation or stress due to uneven cooling at the last moment.

[0094] Combination Figure 2 A schematic diagram of the temperature oscillation growth curve. Figure 2 The operational features of the method of the present invention are demonstrated. A curve is plotted with growth time as the horizontal axis and substrate temperature as the vertical axis, which fluctuates periodically around the horizontal center line, representing the target growth temperature T0 set in S3, such as 700℃. Figure 2 The amplitude (e.g., ±15℃) and period (e.g., 60 seconds) of the oscillation are clearly indicated.

[0095] Figure 3 This is a comparison chart of the thickness distribution of epitaxial wafers after traditional isothermal growth and temperature oscillation growth. Figure 3 The effects can be directly compared by using side-by-side contour maps or two-dimensional mapping maps. Figure 3 The left side simulates the isothermal growth results without initiating the temperature oscillation program in step S5 (i.e., the comparative example). Its thickness contour lines usually show regular changes or irregular distributions from the center to the edge, with obvious color gradients, which intuitively show the continuous uneven growth trend. Figure 3 The right-hand sub-figure corresponds to the result after performing steps S5 and S6 of the present invention. Its thickness contour lines should be more uniform and denser, and the color changes should be smoother.

[0096] Figure 3 This invention provides visual evidence of what it can achieve: forcing the epitaxial layer to grow in a more two-dimensional layered pattern, thus achieving macroscopic height uniformity and effectively solving the technical problem of uneven thickness in traditional methods.

[0097] Figure 4 Provides 3D topographic images of wafer surfaces grown under conventional isothermal conditions. Figure 4 This is an atomic force microscopy (AFM) presentation of the three-dimensional morphology of the surface of a conventionally isothermally grown epitaxial layer at the nanoscale (1×1μm scanning range). Figure 4The middle surface has significant undulations, showing prominent island-like structures, step clusters, or random protrusions. Figure 4 The RMS roughness value (e.g., greater than 0.5 nm) marked in the figure is a key quantitative indicator. Figure 4 As a benchmark, the migration and arrangement of surface atoms under the isothermal growth mode may not be ideal, and there may be intrinsic surface roughening or three-dimensional growth tendency. This corresponds to the microscopic inhomogeneity problem caused by local microenvironment differences mentioned in the technical background.

[0098] Figure 5 This is a 3D morphology image of the wafer surface under temperature oscillation growth. Figure 5 Is with Figure 4 A surface 3D topography image with the same scanning scale and display conditions is used to demonstrate the surface of the epitaxial layer obtained by the method of the present invention. Figure 5 The surface morphology should be significantly smoother, with clear and regular atomic steps. Figure 5 The RMS roughness value (e.g., less than 0.2 nm) indicated in the text is compared to Figure 4 reduce. Figure 5 This is another key effect of verifying the invention at the microscopic scale. Figure 5 This study demonstrates that periodic temperature perturbation, through promoting-buffering cycles, indeed enhances atomic migration and suppresses aberrant adsorption, resulting in a more atomically smoother surface. This confirms that this method improves crystal quality, reduces surface defect states, and provides morphological evidence for superior electrical and optical properties of the epitaxial layer.

[0099] In one embodiment of the present invention, based on step S5, the following is a possible embodiment and its specific implementation is described in a non-limiting manner. In S5, the group III source gas and the group V source gas are introduced into the reaction chamber, and the temperature oscillation program is started simultaneously, so that the temperature of the substrate follows the amplitude and period set in S4. Specifically, this includes the following steps: S51: Confirm that the airflow, pressure and substrate temperature in the reaction chamber have stabilized at the target process parameters set in S3, and enter the preparation state.

[0100] In one embodiment, MOCVD growth is extremely sensitive to initial conditions. Stable temperature, pressure, and gas flow are the physical basis for ensuring growth rate, material composition, and doping uniformity. Temperature stability means that heater power output is balanced with heat loss, and there are no thermal gradients within the substrate and pedestal. Stable pressure indicates that the inlet and outlet gas rates are balanced, which determines the mean free path and residence time of gas molecules, thus affecting precursor transport efficiency and reaction rate. Stable gas flow ensures the uniform spatial distribution of reactants above the substrate.

[0101] S52: Controls the gas flow path switching, introduces V-type source gas from the flow rate set in S3 into the reaction chamber, and maintains this flow.

[0102] In one embodiment, the flow line to the reaction chamber for a Group V source (such as arsine, AsH3) is opened to a preset flow rate value in S3 via a mass flow controller (MFC) or pneumatic valve. Simultaneously, the flow rate of the carrier gas (hydrogen) may be fine-tuned to maintain a stable total gas flow rate, thereby minimizing disturbance to the established flow field inside the reaction chamber. The Group V source gas is mixed with the carrier gas in a mixing chamber or gas injector and then delivered above the reaction chamber. This operation precedes the introduction of the Group III source gas to pre-establish an excess, stable Group V (As) atmosphere on the substrate surface.

[0103] S53: After introducing the Group V source gas, wait for a preset delay time, and then start the flow path of the Group III source gas from the flow rate set in S3.

[0104] In one embodiment, this delay time can be set between 5 and 30 seconds, depending on the reaction chamber volume, gas flow rate, and required surface coverage. Before reaching the substrate surface, the Group III source gas mixes with the already stabilized Group V source / carrier gas in the flow path. This delay ensures that the Group V source gas flow has sufficient time to completely replace the original atmosphere within the reaction chamber and form a uniform, saturated Group V element coverage across the entire substrate surface.

[0105] S54: At the same time as opening the Group III source gas flow path or within 1-3 seconds thereafter, a start command is sent to the temperature controller of the MOCVD equipment to trigger the execution of the temperature oscillation program set in S4.

[0106] In one embodiment, within the time frame of issuing the command to open the Group III source gas flow path, the system's temperature control unit immediately receives a trigger signal to initiate an oscillation program. A PID controller or multi-segment programmable controller with advanced programming capabilities then loads and executes the temperature curve preset in S4. This curve uses the target growth temperature T0 set in S3 as a reference value, and periodically operates as a triangular wave, sine wave, or other waveform, consisting of rising from T0 to T0+15°C and falling from T0+15°C to T0-15°C. The controller dynamically adjusts the heater power based on real-time feedback from the temperature sensor, driving the substrate temperature to follow the preset oscillation trajectory.

[0107] S55: After the temperature oscillation program is started, the temperature sensor data monitored in real time confirms that the substrate temperature has entered a periodic oscillation trajectory based on the target growth temperature set in S3. At this time, epitaxial layer growth begins.

[0108] In one embodiment, after the temperature oscillation program is initiated, the system continuously reads signals from a temperature sensor on the substrate or base. The monitoring system compares these real-time temperature data with parameters set in S4, including a reference temperature T0, amplitude A, and period T.

[0109] Verification includes: 1) Whether the actual temperature trajectory quickly tracks the set curve; 2) Whether the peak and trough values ​​of the oscillation are stable within the range of T0±A; 3) Does the oscillation period match the set period T? Typically, it is required that within 2-3 complete cycles after startup, the deviation between the actual temperature trajectory and the set trajectory should converge to within ±1℃ and exhibit stable periodicity. Once these conditions are confirmed, the system determines that "epitaxy layer growth" has officially commenced in the designed temperature oscillation mode. S6's thickness control will be based on this confirmed stable oscillation process, using timing or in-situ monitoring. This ensures process stability and provides crucial actual temperature curves for subsequent process optimization.

[0110] In one embodiment of the present invention, based on step S5, the following is a possible embodiment and its specific implementation is described in a non-limiting manner. In S5, periodic oscillations are performed around the target growth temperature set in S3 to begin epitaxial layer growth, specifically including the following steps: Step S511: High-purity Group V source gas is introduced into the MOCVD reaction chamber to replace the residual hydrogen gas in the chamber and maintain the preset atmosphere parameters. Here, arsine molecules are adsorbed and decomposed on the substrate surface to form a dense arsenic atom coating, which isolates the substrate from contact with residual hydrogen gas and prevents the cleaned surface from being oxidized or contaminated.

[0111] Step S512: Start the Group III source gas in a gradient-increment manner, adjust the flow rate to the target value set in S3, and monitor the pipeline stability.

[0112] Optionally, open the valve of the trimethylgallium source bottle and set the gradient increase rate of the flow controller to 4 sccm / 8 seconds, gradually increasing it from 0 sccm to 20 sccm (corresponding to a V / III ratio of 50). After each flow adjustment, wait for a preset time and then read the data from the source pipeline pressure sensor to ensure that the pipeline pressure fluctuation is less than ±0.08 bar, until the flow rate stabilizes at the target value.

[0113] Step S513: After the group III source flow rate stabilizes, start the temperature oscillation program to make the substrate temperature oscillate around the target growth temperature set in S3 according to the parameters in S4.

[0114] When the trimethylgallium flow rate stabilizes at 20 sccm and the pipeline pressure fluctuation remains less than ±0.08 bar for one minute, an oscillation start command is sent through the temperature control interface. The temperature oscillation program drives the infrared heating module to begin the first heating cycle at the target growth temperature of 700℃, with a 60-second cycle and ±15℃ amplitude set in S4. Simultaneously, temperature data is collected in real time via thermocouples to ensure the synchronization of the oscillation phase with the source supply. This precise synchronization between the initial stage of temperature oscillation and source supply improves the initial uniformity of the epitaxial layer.

[0115] In one embodiment of the present invention, the following steps are included after S2: S211: Under a hydrogen atmosphere, the temperature of the thermally cleaned substrate is reduced from a first preset temperature to a second preset temperature and maintained at the second preset temperature for a period of time.

[0116] Alternatively, at a temperature of around 600°C, AsH3 can be effectively decomposed to produce active As atoms or As2 molecules. These active species will adsorb onto all available bonding sites on the GaAs substrate surface.

[0117] S212: At the second preset temperature, introduce a Group V source gas into the reaction chamber and establish a stable partial pressure, but do not introduce a Group III source gas, and maintain this state for 1 to 5 minutes.

[0118] S213: The substrate temperature is increased from the second preset temperature to the third preset temperature at a controllable rate, wherein the third preset temperature is lower than the target growth temperature T0 set in S3.

[0119] In one embodiment, while maintaining a continuous flow of Group V source gas, the control system instructs the heater to increase its power, raising the substrate temperature from a second preset temperature (e.g., 600°C) to a new temperature point, namely a third preset temperature. This heating process is not necessarily faster; the rate needs to be controlled between 10°C and 25°C per minute to ensure temperature uniformity and avoid thermal stress. The value of the third preset temperature is lower than the target temperature T0 for formal oscillation growth (e.g., 700°C), but higher than the previous passivation temperature. Its typical range is between T0 minus 30°C and T0 minus 80°C; for example, for T0 = 700°C, the third preset temperature could be set to 660°C.

[0120] S214: At the third preset temperature, a group III source gas and a group V source gas are simultaneously introduced to grow an initial buffer layer with a thickness of 10 to 50 nanometers at a constant temperature.

[0121] S215: Turn off the group III source gas, and under the group V source gas atmosphere, raise the substrate temperature from the third preset temperature to the target growth temperature T0 set in S3 at a specific rate, and stabilize it for 1 to 3 minutes after reaching T0.

[0122] In one embodiment, under this protective atmosphere, the control system instructs the heater to increase its power again, raising the substrate temperature from a third preset temperature (e.g., 660°C) to the final target growth temperature T0 (e.g., 700°C). Once the temperature sensor confirms that T0 has been reached and stabilized within ±2°C, a holding phase begins, lasting 1 to 3 minutes. After this phase, the substrate is in a thermodynamically stable, pre-growth state with a well-defined surface chemical environment. This is followed by step S5, where the epitaxial growth of the host layer begins.

[0123] In one embodiment of the present invention, the following steps are further included between S5 and S6: S611: After the temperature oscillation program is started and runs stably for 5 to 10 complete cycles, the in-situ optical thickness monitoring system is started. Based on the oscillation frequency of the monitored reflection signal, the transient growth rate is deduced and recorded in real time.

[0124] In one embodiment, the oscillation frequency of the laser reflection signal has a defined mathematical relationship with the optical constants and physical growth rate of the material. Given the material's refractive index, the physical thickness increase corresponding to each complete oscillation cycle of the reflection signal is constant.

[0125] Furthermore, by measuring the duration of the oscillation period, the average growth rate within that time period can be directly calculated. Under temperature oscillation conditions, this instantaneous rate itself also fluctuates periodically. Taking its average over a period of time provides a reliable indicator reflecting the true deposition efficiency under current macroscopic process conditions.

[0126] S612: Compare the continuously recorded transient growth rate with a theoretical average growth rate pre-calculated based on process parameters. If the average measured rate of multiple consecutive cycles deviates from the theoretical value by more than ±3%, then adjust the mass flow rate setting of the Group III source gas proportionally, with the adjustment range not exceeding ±5% of the original setting value.

[0127] In one embodiment, during MOCVD growth, under constant temperature and pressure, the growth rate is primarily determined by the flux of Group III precursors reaching the surface, and this flux is essentially linearly related to the setpoint of the mass flow controller. Therefore, the most direct way to correct growth rate deviations is to fine-tune the Group III source flow rate. Fine-tuning based on measured rates after oscillation stabilization is chosen to eliminate long-term system drift.

[0128] S613: When the epitaxial layer thickness is confirmed to reach about one-third of the preset total thickness through time integration or in-situ monitoring, while maintaining temperature oscillation, the flow rate of the group V source gas is temporarily increased by 20% to 40% on the original basis, and this high flow rate is maintained for 2 to 5 complete temperature oscillation cycles, after which the original flow rate is restored.

[0129] In one embodiment, a brief, high V / III ratio growth interval is introduced at approximately one-third of the thickness during the middle of the growth process, acting similarly to a single chemical annealing step. The V-group atmosphere, under high-temperature oscillating conditions, effectively suppresses Ga vacancy formation and provides chemical potential for surface atoms.

[0130] S614: When the epitaxial layer thickness reaches about two-thirds of the preset total thickness, a correction instruction is embedded in the temperature control program so that the starting point of the cooling phase of each temperature oscillation cycle is changed from a fixed T0+ amplitude value to a value dynamically determined based on the actual temperature peak of the previous cycle, with the value fluctuating within the range of -2℃ to +1℃ of the previous peak temperature.

[0131] In one embodiment, the temperature control logic changes when the epitaxial layer growth enters the later stage and the thickness reaches approximately two-thirds of the total target.

[0132] Previously, the starting point for cooling in each oscillation cycle was a fixed number, such as 715℃. After that, the actual peak temperature reached in the previous complete oscillation cycle was read. The starting point for cooling in the next cycle will no longer be a fixed 715℃, but a value randomly selected or according to a preset pattern within a very small range (-2℃ to +1℃) based on the previous actual peak temperature.

[0133] If the peak temperature of the previous cycle was 714.8℃, then the starting point for the next cooling cycle could be set at 713.8℃, 714.8℃, or 715.8℃. The heating phase will still start from the trough and rise to this dynamically determined starting point.

[0134] S615: When the growth process enters the final stage and the estimated thickness reaches 85% to 90% of the target thickness, an oscillation convergence subroutine is initiated. This subroutine controls the amplitude of the temperature oscillation to decrease linearly by 5% to 10% in each subsequent cycle until the amplitude decays to less than 20% of the initial value. Then, the continuous growth described in S6 proceeds to the final thickness.

[0135] In one embodiment, the kinetic intensity experienced by the epitaxial layer growth interface is smoothly and progressively reduced by linearly or exponentially decaying the amplitude. The equilibrium position with the lowest energy is found through diffusion, thereby forming a high-quality surface.

[0136] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. A temperature oscillation growth method for improving uniformity of GaAs epitaxial layers, characterized by, The method comprises: S1: configuring a gallium arsenide substrate and placing the gallium arsenide substrate in a reaction chamber of a MOCVD device; S2: under a hydrogen atmosphere, raising the temperature of the gallium arsenide substrate to a first preset temperature and maintaining the temperature, to perform thermal cleaning on the surface of the substrate; S3: setting target process parameters for epitaxial growth, the target process parameters comprising: a target growth temperature, a group III source gas flow rate, a group V source gas flow rate, and a reaction chamber pressure; S4: setting execution parameters of a temperature oscillation program, the execution parameters comprising: an oscillation amplitude and a cycle for periodic oscillation around the target growth temperature; S5: introducing the group III source gas and the group V source gas into the reaction chamber, and starting the temperature oscillation program, so that the temperature of the substrate periodically oscillates around the target growth temperature set in S3 according to the oscillation amplitude and cycle set in S4, and epitaxial layer growth starts; S6: continuously performing epitaxial growth under the control of the temperature oscillation program until the thickness of the epitaxial layer reaches a preset value; S7: stopping the introduction of the group III source gas, and lowering the temperature of the substrate under a group V source gas atmosphere.

2. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein In S2, under a hydrogen atmosphere, the temperature of the substrate is raised to a first preset temperature and maintained, which specifically comprises the following steps: S21: replace the atmosphere in the reaction chamber with a pure hydrogen stream, and raise the temperature of the substrate from room temperature to a treatment temperature of 650-800°C at a temperature raising rate of 10-30°C / s; S22: maintain the gallium arsenide substrate at the treatment temperature under a pure hydrogen atmosphere, control the reaction chamber pressure in the range of 50-200 mbar, and continuously treat for 5-20 minutes; S23: after the completion of the continuous treatment in S22, lower the temperature of the substrate from the treatment temperature to a target growth temperature, which is lower than the treatment temperature and in the range of 600-750°C; S24: after the temperature of the substrate is stabilized at the target growth temperature, switch the gas environment in the reaction chamber from the pure hydrogen atmosphere to a hydrogen carrier gas mixed atmosphere containing a group V source process gas, and stabilize the reaction chamber pressure to a set value required for growth.

3. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein In S5, the temperature of the substrate is introduced into the reaction chamber according to the oscillation amplitude and cycle set in S4 while the temperature oscillation program is started, which specifically comprises the following steps: S51: confirm that the gas flow, pressure, and substrate temperature in the reaction chamber have been stabilized at the target process parameters set in S3, and enter a preparation state; S52: control the gas flow path switching, introduce the group V source gas from the flow rate set in S3 into the reaction chamber, and maintain this gas flow; S53: after introducing the group V source gas, wait for a preset delay time, and then open the group III source gas flow path from the flow rate set in S3; S54: at the same time or within 1-3 seconds after opening the group III source gas flow path, issue a start instruction to the temperature controller of the MOCVD device to trigger the execution of the temperature oscillation program set in S4; S55: After the temperature oscillation program is started, the substrate temperature is confirmed to have entered the periodic oscillation track based on the target growth temperature set in S3 by real-time monitoring of the temperature sensor data, at which time the epitaxial layer growth begins.

4. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein In S5, the periodic oscillation around the target growth temperature set in S3 begins the epitaxial layer growth, which specifically includes the following steps: S511: high-purity group V source gas is introduced into the MOCVD reaction chamber to replace the residual hydrogen in the chamber and maintain the preset atmosphere parameters; S512: the group III source gas is turned on in a gradient increasing manner, the flow rate is adjusted to the target value set in S3, and the pipeline stability is monitored; S513: after the group III source flow is stable, the temperature oscillation program is started to make the substrate temperature oscillate around the target growth temperature set in S3 according to the parameters in S4.

5. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein In S6, the epitaxial growth continues under the control of the temperature oscillation program until the thickness of the epitaxial layer reaches the preset value, which specifically includes the following steps: S61: under the conditions of temperature oscillation process and continuous introduction of reaction gas, the reaction chamber pressure and reaction gas flow rate are monitored and adjusted in real time to stabilize them within the target process parameter range set in S3; S62: real-time temperature data of the gallium arsenide substrate are collected and compared with the target curve of the temperature oscillation program set in S4 to ensure that the amplitude, period and central temperature value of the actual temperature oscillation are maintained within the preset tolerance band; S63: the in-situ optical monitoring device is used to obtain optical signals of the growth surface in real time, and whether the epitaxial layer is in a continuous two-dimensional layer growth mode is judged according to the characteristics of the optical signals; S64: according to the preset target thickness of the epitaxial layer, the growth time is counted or the in-situ film thickness monitoring signal is used to trigger the growth process end instruction when the target thickness is reached.

6. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein In S7, the substrate is cooled under the group V source gas atmosphere, which specifically includes the following steps: S71: when the thickness of the epitaxial layer reaches the preset value, the group III source gas supply is turned off, and an oscillation decay-surface stabilization process is started to drive the substrate temperature to continue to execute 2 to 5 complete temperature oscillation periods with a halved amplitude under the group V source gas atmosphere; S72: after completing the oscillation period, the substrate temperature is controlled to start from the current temperature, first decrease to an intermediate temperature point at a first cooling rate and keep warm for a short time, and then decrease to a preparation temperature at a second cooling rate lower than the first cooling rate; S73: at the preparation temperature, the group V source gas supply is turned off, the atmosphere is switched to pure hydrogen or inert gas, and the substrate is cooled to a temperature at which it can be taken out at a third cooling rate.

7. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein After S2, the following steps are further included: S211: under the hydrogen atmosphere, the temperature of the substrate subjected to thermal cleaning is decreased from a first preset temperature to a second preset temperature, and kept at the second preset temperature for a period of time; S212: under the second preset temperature, the group V source gas is introduced into the reaction chamber to establish a stable partial pressure, but the group III source gas is not introduced, and the state is maintained for 5 minutes; S213: the substrate temperature is increased to a third preset temperature at a controllable rate from the second preset temperature, and the third preset temperature is lower than the target growth temperature T0 set in S3; S214: at the third preset temperature, group III source gas and group V source gas are introduced simultaneously, and an initial buffer layer with a thickness of 10-50 nm is grown at a constant temperature; S215: the group III source gas is turned off, the substrate temperature is raised from the third preset temperature to the target growth temperature T0 set in S3 at a preset rate under the group V source gas atmosphere, and is stabilized for 1-3 minutes after reaching T0.

8. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein, The method further comprises the following steps between S5 and S6: S611: after the temperature oscillation program is started and stably runs for 5-10 complete cycles, an in-situ optical thickness monitoring system is started, and the instantaneous growth rate is real-time back-calculated and recorded according to the monitored reflection signal oscillation frequency; S612: the continuously recorded instantaneous growth rate is compared with a theoretical average growth rate calculated according to the process parameters in advance, if the average measured rate of multiple cycles deviates from the theoretical value by more than ±3%, the mass flow rate set value of the group III source gas is proportionally adjusted, and the adjustment amplitude is not more than ±5% of the original set value; S613: when the thickness of the epitaxial layer reaches about one-third of the preset total thickness by time integration or in-situ monitoring, the group V source gas flow is temporarily increased by 20%-40% on the basis of the original flow while maintaining the temperature oscillation, and the high flow state is maintained for 2-5 complete temperature oscillation cycles, and then the original flow is restored; S614: when the thickness of the epitaxial layer reaches about two-thirds of the preset total thickness, a correction instruction is embedded in the temperature control program, so that the starting point of the temperature drop stage of each temperature oscillation cycle is changed from a fixed T0+amplitude value to a dynamic value determined according to the actual temperature peak value of the previous cycle, and the value is floating in the range of-2°C to +1°C of the previous peak temperature; S615: when the growth process enters the last stage and the thickness is estimated to be in the range of 85%-90% of the target thickness, an oscillation convergence sub-program is started, the oscillation convergence sub-program controls the amplitude of the temperature oscillation to linearly decrease by 5%-10% in each subsequent cycle until the amplitude is attenuated to less than 20% of the initial value, and then the continuous growth to the final thickness in S6 is entered.

9. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein, The method further comprises the following steps after S6: S621: when the thickness of the epitaxial layer reaches a predetermined value before a predetermined time or a predetermined thickness, the amplitude of the temperature oscillation program is started to be gradually reduced; S622: after the amplitude is reduced to zero or a preset minimum value, the substrate temperature is maintained at the target growth temperature set in S3, and the group III source gas and the group V source gas are introduced, and the process is continued for a predetermined time; S623: after the continuous introduction in S622 is completed, the group III source gas flow is linearly reduced to zero within 2-5 seconds, and then S7 is performed.

10. The temperature oscillation growth method for improving uniformity of GaAs epitaxial layers according to claim 1, wherein The method is suitable for growing gallium arsenide material, aluminum gallium arsenide or indium gallium arsenide epitaxial layers.

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