Remote plasma source load impedance disturbance protection control method and device

Abstract

The invention belongs to the technical field of remote plasma sources, and provides a remote plasma source load impedance disturbance protection control method and device. The method comprises the following steps: collecting gas flow, gas pressure and reaction chamber temperature of a reaction chamber; obtaining a load impedance prediction value according to the load impedance prediction model; and controlling the system to work in a constant power stage or a constant current stage according to whether the load impedance predicted value F is in a fluctuation stable interval. According to the method, the load impedance value F can be predicted by using the load impedance prediction model under different gas flows, pressures and cavity temperatures, whether the working state is stable or not is determined according to the load impedance value, and the system is controlled to work in a constant power stage or a constant current stage. Gas load fluctuation and plasma dynamic real-time cooperative regulation and control are achieved, mixing disturbance during gas switching is effectively restrained, and the problem of plasma instability is solved; the situation that a power device is damaged due to overlarge current caused by gas load fluctuation is avoided, and the service life of the remote plasma source is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of remote plasma sources, and particularly to a method and device for protecting and controlling the load impedance perturbation of a remote plasma source. Background Art

[0002] In high-end industrial fields such as semiconductor manufacturing, thin film deposition, and material surface modification, remote plasma sources (RPS) are widely used due to their unique advantages. Different from traditional direct plasma technology, remote plasma sources physically separate the plasma generation region from the reaction region, effectively avoiding the direct bombardment of sensitive substrates by high-energy ions, and at the same time achieving uniform distribution of active particles through long-range transmission. However, this decoupled design also introduces new challenges: fluctuations in gas load (such as instantaneous changes in flow rate, pressure, or composition) can significantly affect the stability and reaction characteristics of the plasma, thereby leading to a decrease in process repeatability, deterioration of film uniformity, and even shortening of equipment life.

[0003] Research shows that the gas transmission path of remote plasma sources is relatively long, and the gas is easily disturbed by factors such as pipeline impedance, pumping speed of the vacuum pump, and precursor injection timing during the flow process, forming dynamic load fluctuations. This kind of fluctuation affects the process quality through two mechanisms: First, the non-steady change of the gas state directly leads to the fluctuation of the plasma ionization efficiency, resulting in the drift of the concentration of active particles, such as free radicals and excited substances; Second, the transient fluctuation of the gas load will change the impedance characteristics of the plasma, causing a decrease in the coupling efficiency of radio frequency (RF) or microwave power, and further amplifying the instability of plasma parameters such as electron density and ion energy distribution. Although existing research has achieved macroscopic flow control through gas mass flow controllers (MFCs) and pressure feedback systems, there is still a lack of effective suppression means for transient fluctuations in the microsecond to millisecond range.

[0004] Although the problem of gas load fluctuation in remote plasma sources (RPS) has attracted wide attention, the existing protection and control technologies still have the following key defects: 1. Insufficient dynamic response speed: The response time of existing gas control systems (such as mass flow controllers MFCs and pressure sensors) is usually in the millisecond to hundreds of millisecond range, and it is difficult to effectively capture transient fluctuations in the microsecond to millisecond range (such as pressure oscillations during pulsed gas supply or mixing perturbations during gas switching). This kind of lag causes the control system to be unable to match the dynamic changes of the plasma impedance in real time, thereby triggering RF power reflection or plasma instability.

[0005] 2. Limitations of the linearization assumption of the control model: Traditional control strategies (such as the PID algorithm) are based on linear or weakly nonlinear assumptions, while the gas-plasma coupling process of remote plasma sources has strong nonlinear and time-varying characteristics (such as the exponential relationship between gas dissociation rate and flow rate, and the dynamic fluctuations of plasma sheath impedance). Such models are difficult to accurately describe the interaction effects of multiple physical fields, resulting in control parameters deviating from the optimal range.

[0006] 3. Lack of multi-parameter coupling regulation: The influence of gas load fluctuations usually involves the coordinated changes of multiple parameters such as gas flow rate, pressure, and temperature. However, existing protection controls mostly adopt isolated parameter feedback mechanisms and lack global optimization of the gas-plasma-electromagnetic field coupling relationship. For example, when adjusting the flow rate only through pressure compensation, the reverse interference of plasma impedance changes on power coupling efficiency may be ignored.

[0007] 4. Insufficient adaptability to complex working conditions: In advanced processes such as pulsed modulated plasma and multi-gas path alternating injection, gas load fluctuations exhibit high-frequency and non-periodic characteristics. Existing control algorithms rely on fixed thresholds or empirical rules and are difficult to dynamically adjust control strategies, resulting in a decrease in process repeatability (such as the film thickness deviation exceeding ±5%). Summary of the Invention

[0008] In view of the defects in the prior art, the present invention provides a method and device for protecting and controlling the load impedance perturbation of a remote plasma source to solve the problem that a high-precision regulation mechanism for multi-physical field cooperation is urgently needed for current remote plasma sources.

[0009] In the first aspect, a method for protecting and controlling the load impedance perturbation of a remote plasma source provided by the present invention includes the following steps after the reaction chamber is normally ignited: Collect the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber; Obtain a predicted value F of the load impedance according to the load impedance prediction model; According to whether the predicted value F of the load impedance is within the fluctuation stable range, the control system operates in the constant power stage or the constant current stage; if the predicted value of the load impedance is within the fluctuation stable range, the control system operates in the constant power stage, otherwise the control system operates in the constant current stage.

[0010] As can be seen from the above technical solutions, the method for protecting and controlling the load impedance perturbation of a remote plasma source provided by the present invention can use the load impedance prediction model to predict the load impedance value F under different gas flow rates, gas types, and chamber temperature changes. When the system is in the ignition working stage or the predicted load impedance is unstable, it operates in the constant current stage and outputs a constant current near the resonance frequency point to avoid damage to power devices due to excessive current; when the predicted load impedance is stable, the system automatically enters the constant power mode to keep the power output constant.

[0011] Optionally, the load impedance prediction model is ; Z is the load impedance, k1, k2, k3 are variable coefficients, and k0 is a constant term; The objective function is , Q i , P i , t i , Z i are n groups of data, ; The predicted value F of the load impedance is determined by fitting the variable coefficients and the constant term.

[0012] Optionally, the fitting method for the variable coefficients and the constant term includes: Construct a data matrix X and an observation vector Z; ; Take the partial derivative of the variable vector to be solved and set the derivative to zero to obtain the normal equation ; The optimal solution of the variable to be solved .

[0013] Optionally, the fluctuation stable interval is , is the average value of multiple predicted values F of the impedance obtained by sampling at intervals of the sampling period T within the unit time T0, and d is the load impedance fluctuation error. s

[0014] Optionally, the constant current stage includes: According to the resonant output current reference value and the sampled current i pri obtain the current error e1, and output the duty cycle d through the current PI modulator; Output the PWM drive signals D1~D4 of the inverter switching tubes through PWM modulation.

[0015] Optionally, the constant power stage includes: Compare the output power reference value P ref with the resonant output voltage V loop and the current i pri to obtain the actual power Po, and output the power error e0. After power PI modulation, obtain the resonant output current reference value i ref ; Compare the current reference value i ref with the current value i pri sampled by the power circuit to obtain the current error e1, and output the duty cycle d through the current PI modulator; Obtain the switching frequency f by modulating the current error e1 through PI and taking the inverses , the PWM drive signals D1 - D4 of the inverter switching tubes are output through PWM modulation.

[0016] In a second aspect, a remote plasma source load impedance perturbation protection control device provided by the present invention includes: An acquisition module for acquiring the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber; An impedance prediction module for obtaining a predicted load impedance value F according to a load impedance prediction model; An anti - perturbation control module for controlling the system to operate in a constant - power stage or a constant - current stage according to whether the predicted load impedance value F is within a fluctuation - stable interval; if the predicted load impedance value is within the fluctuation - stable interval, the system operates in the constant - power stage, otherwise the system operates in the constant - current stage.

[0017] Adopting the above - mentioned technical solution, the present application has the following beneficial effects: The present invention can use a load impedance prediction model to predict the load impedance value F under different gas flow rates, gas types, and chamber temperature changes, determine whether the working state is stable according to the load impedance value, the system operates in the constant - current stage during the ignition working stage or when the predicted load impedance is unstable, performs constant - current output near the resonance frequency point to avoid damaging power devices due to excessive current; when the predicted load impedance is stable, the system automatically enters the constant - power mode to keep the power output constant. Description of the Drawings

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0019] Figure 1 Shows a control block diagram of a remote plasma source provided by an embodiment of the present invention; Figure 2 Shows a flowchart of a method for protecting and controlling the load impedance perturbation of a remote plasma source provided by an embodiment of the present invention; Figure 3 Shows an application flowchart of a method for protecting and controlling the load impedance perturbation of a remote plasma source provided by an embodiment of the present invention; Figure 4 Shows a structural block diagram of a remote plasma source load impedance perturbation protection control device provided by an embodiment of the present invention. Detailed Embodiments

[0020] The embodiments of the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and thus are only examples and cannot be used to limit the protection scope of the present invention. It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0021] As Figure 1 shown, a control block diagram of a remote plasma source is provided, including a remote plasma source power circuit, a constant current stage unit, and a constant power stage unit; the remote plasma source power circuit includes a control unit, a PWM drive unit, a DC / AC resonant converter, an ignition circuit, a sustaining circuit, a sampling unit, and a reaction chamber; the control unit is used to control the PWM drive unit to output a pulse signal; the PWM drive unit controls the output current of the resonant converter; the output current of the resonant converter affects the input current of the ignition circuit; the resonant converter converts the pulse signal output by the PWM drive unit into an AC source and is used to provide an input AC source for the ignition circuit; the ignition circuit generates a high-voltage ignition signal to cause the plasma load to oscillate and ionize at high frequency, and the resonant converter is used to provide the input AC source; the resonant converter includes a transformer T1, and the ignition circuit is connected to the secondary coil N3 of the transformer T1. The power circuit further includes a sustaining circuit, and the sustaining circuit is connected in series with the secondary coil N2 of the transformer T. The vacuum reaction chamber is used as the secondary side of the high-frequency transformer and can only provide io for the chamber to meet the low-voltage energy input in the ionization maintenance stage; the sustaining circuit is used to maintain the bus voltage stable after entering the constant power stage (ionization stage) from the constant current stage (ignition stage) when the relay is disconnected; the sampling unit is used to collect the ignition current of the ignition circuit, and the output voltage and output current of the resonant converter; the relay is controlled by the control unit to be attracted or disconnected.

[0022] As Figure 2 shown, a method for protecting and controlling the load impedance perturbation of a remote plasma source is provided. After the reaction chamber is normally ignited, the method includes: S1. Collect the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber.

[0023] The above parameters are collected by a multi-sensor module. The multi-sensor module includes a gas flow meter, a pressure sensor, and a temperature sensor to monitor the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber respectively.

[0024] S2. Obtain a predicted value F of the load impedance according to the load impedance prediction model.

[0025] In a remote plasma system, the influence of the gas flow rate Q, gas pressure P, and reaction chamber temperature T on the load impedance can be described by the following ideal gas model: When the pumping speed S of the vacuum pump is fixed, the pressure P is proportional to the flow rate P = Q / S. The load impedance Z is proportional to the flow rate and inversely proportional to the temperature T. The influence of the gas flow rate Q on the load impedance Z can be expressed by Equation (1): (1) where is a proportionality constant related to system parameters such as electrode area, collision cross-section, etc.

[0026] At a constant temperature, the load impedance is proportional to the pressure: (2) where is a proportionality constant related to plasma density and collision frequency.

[0027] At a constant pressure, due to the decrease in gas density, the load impedance is inversely proportional to the reaction chamber temperature: (3) where is a proportionality constant.

[0028] Among them, the load impedance prediction model in step S2 is (4) Z is the load impedance, k1, k2, k3 are variable coefficients, and k0 is a constant term; Q i , P i , t i , Z i are n groups of observed data, ; The predicted value F of the load impedance is determined by fitting the variable coefficients and the constant term.

[0029] Optionally, the fitting method for the variable coefficients and the constant term includes: Construct a data matrix X and an observation vector Z; (5) The objective function of the least squares method is to minimize the sum of squared residuals: (6) Take the partial derivative of the variable vector to be solved and set the derivative to zero to obtain the normal equation: (7) The optimal solution of the variable to be solved (8). Substitute the obtained optimal solution of the parameters into Equation (4) to obtain the current predicted value F of the load impedance.

[0030] S3. Determine whether the predicted value F of the load impedance is within the fluctuation stability range, and the control system operates in the constant power stage or the constant current stage; if the predicted value of the load impedance is within the fluctuation stability range, the control system operates in the constant power stage, otherwise the control system operates in the constant current stage.

[0031] In step S3, the fluctuation stability range is , is the average value of multiple obtained impedance predicted values F sampled at intervals of sampling period T within unit time T0, and d is the load impedance fluctuation error. s Using the above method, the load impedance value F can be predicted by using the load impedance prediction model under different gas flow rates, gas types, and chamber temperature changes. When the system is in the ignition working stage or the predicted load impedance is unstable, it operates in the constant current stage, outputs a constant current near the resonance frequency point, and avoids damaging the power device due to excessive current; when the predicted load impedance is stable, the system automatically enters the constant power mode to keep the power output constant.

[0032] See

[0033] See Figure 1 , the constant current stage includes: Obtain the current error e1 according to the resonance output current reference value and the sampled current i pri , and output the duty cycle d through the current PI modulator; Output the PWM drive signals D1~D4 of the inverter switching tubes through PWM modulation.

[0034] See Figure 1 , the constant power stage includes: Compare the output power reference value P ref with the resonance output voltage V loop and the current i pri to obtain the actual power Po, compare the output power error e0, and obtain the resonance output current reference value i ref after power PI modulation; Compare the current reference value i ref with the current value i pri sampled by the power circuit to obtain the current error e1, output the duty cycle d through the current PI modulator; Obtain the switching frequency f by PI modulating and inverting the current error e1 s , and output the PWM drive signals D1~D4 of the inverter switching tubes through PWM modulation.

[0035] As Figure 3 shown, a remote plasma source load impedance perturbation protection control method provided by this embodiment, in specific applications, the process is as follows: Step A1: After the remote plasma source is powered on and running, first, the system sets the gas current excitation threshold imin, and introduces the excitation gas. Through the stage adjustment unit, when the stage adjustment unit is at 50 ms before the ignition operation, the resonant output current reference value is instantaneously reduced to the current reference value , which can effectively avoid inrush current and play a role in protecting the relay S; Step A2: Determine whether an ignition signal is received. If an ignition command is received, drive and output to engage the relay S. Otherwise, the system continues to introduce the excitation gas; Compare the resonant output current reference value with the current value ipri sampled by the power circuit and output the current error . After current PI modulation, start the PWM drive unit. Determine whether imin ≤ ipri ≤ imax and it is maintained for more than 500 ms. If it is satisfied, then continue to determine whether the system ignites successfully. Otherwise, report an error for ignition failure and disconnect the relay S; Step A3: If it is determined that the ignition is abnormal, increase the duty cycle d in the constant current stage, so that the resonant output voltage Vloop increases and the output power rises. The ignition voltage Vcd in the ignition circuit passing through the coupling transformer T1 also increases accordingly. Then, determine again whether the ignition is normal. When the ignition is successful, jump to the step of disconnecting the relay S; If it is determined that the ignition fails, perform cyclic ignition processing. The upper limit of the number of cycles is N times to improve the ignition success rate; If the ignition is still not successful after exceeding the cycle upper limit, it is determined that the ignition fails and the system reports an error and disconnects the relay S; Step A4: Use the load impedance prediction model to output the predicted value of the load impedance . In the actual working condition, increasing the output power of the plasma source will cause fluctuations in the load impedance. Therefore, the system operates in the constant current stage during the ignition working stage or when the predicted load impedance is unstable; that is or when, the system enters the constant current stage. Due to the circuit characteristics of the LCL resonant converter in the constant current stage, after fixing the hardware parameters such as fixed resistance, inductance, and capacitance, the system operates near the resonant frequency point for constant current output to keep the output current constant and avoid damaging the power devices due to excessive current. When the predicted load impedance is stable, that is when, where d is the load impedance fluctuation error, the system automatically enters the constant power mode to keep the power output constant; The control process of the constant power stage includes: Multiply the output power reference value P ref by the resonant output voltage V loop and the current i pri to obtain the actual power P oAfter comparison, the output power error e0 is used to obtain the resonant output current reference value i through power PI modulation. ref The current reference value i ref is compared with the current value i pri sampled by the power circuit to output the current error e1. The duty cycle d is output through the current PI modulator; the current error e1 passes through the PI modulator and is inverted to obtain the switching frequency f. s Finally, the PWM drive signals D1~D4 of the inverter switching tubes are output through the PWM drive unit.

[0036] In one embodiment, as Figure 4 shown, a remote plasma source load impedance perturbation protection control device 40 is provided, including: An acquisition module 401 for acquiring the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber; An impedance prediction module 402 for obtaining a load impedance prediction value F according to the load impedance prediction model; An anti-perturbation control module 403 for controlling the system to operate in a constant power stage or a constant current stage according to whether the load impedance prediction value F is in the fluctuation stable range; if the load impedance prediction value is within the fluctuation stable range, the system operates in the constant power stage, otherwise the system operates in the constant current stage.

[0037] The remote plasma source load impedance perturbation protection control device 40 provided by the embodiment of the present application and the above-mentioned remote plasma source load impedance perturbation protection control method adopt the same inventive concept and can achieve the same beneficial effects, which will not be elaborated here.

[0038] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as the combinations of these technical features do not conflict, they should be considered as the scope recorded in this specification.

[0039] The above-described embodiments only represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A protection control method for load impedance perturbation of a remote plasma source, characterized in that, Including: Collecting the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber; Obtaining a predicted load impedance value F according to the load impedance prediction model; Controlling the system to operate in a constant power stage or a constant current stage according to whether the predicted load impedance value F is within a fluctuating stable range; if the predicted load impedance value is within the fluctuating stable range, the system operates in the constant power stage, otherwise the system operates in the constant current stage.

2. The method according to claim 1, characterized in that, The load impedance prediction model is ; Z is the load impedance, k1, k2, k3 are variable coefficients, and k0 is a constant term; The objective function is , Q i , P i , t i , Z i are n groups of data, ; The predicted load impedance value F is determined by fitting variable coefficients and constant terms.

3. The method according to claim 2, characterized in that The fitting method for the variable coefficients and constant terms includes: Construct the data matrix X and the observation vector Z; ; Treat the variable vector to be solved Take the partial derivative and set the derivative to zero to obtain the normal equation ; Optimal solution of the variable to be solved .

4. The method according to claim 1, characterized in that, The fluctuation stable range is , is the average value of multiple impedance prediction values F obtained at intervals of sampling period T within unit time T0, and d is the load impedance fluctuation error. s ​ 5. The method according to claim 4, wherein The constant current stage includes: According to the reference value of the resonant output current and the sampled current i pri obtain the current error e1, and output the duty cycle d through the current PI modulator; Outputting PWM drive signals D1 to D4 of the inverter switch tubes through PWM modulation.

6. The method according to claim 5, characterized in that, The constant power stage includes: According to the output power reference value P ref , the resonant output voltage V obtained by sampling loop and the current i pri , the actual power Po is obtained. After comparing the output power error e0, the resonant output current reference value i is obtained after power PI modulation ref ; Compare the current reference value i ref with the current value i pri sampled by the power circuit, and output the current error e1. Output the duty cycle d through the current PI modulator; The current error e1 is modulated by PI and inverted to obtain the switching frequency f s , and the PWM drive signals D1~D4 of the inverter switching tubes are output through PWM modulation.

7. A remote plasma source load impedance perturbation protection and control device, characterized in that, Including: A collection module for collecting the gas flow rate Q, gas pressure P, and reaction chamber temperature T of the reaction chamber; An impedance prediction module for obtaining a predicted load impedance value F according to the load impedance prediction model; A disturbance rejection control module for controlling the system to operate in a constant power stage or a constant current stage according to whether the predicted load impedance value F is within a fluctuating stable range; if the predicted load impedance value is within the fluctuating stable range, the system operates in the constant power stage, otherwise the system operates in the constant current stage.

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