Power section control method and system of pulse radio frequency power supply

Abstract

The invention discloses a power section control method and system of a pulse radio frequency power supply. The power section control method adopts three control stages which are executed according to a time sequence; the method specifically comprises the steps that S1, open-loop fixed gain driving is adopted, and the driving gain of the radio frequency amplifier is fixed to be a first threshold value within a first preset time period; s2, a closed-loop control loop is started, and constant load power control is adopted in a second preset time period; and S3, adopting constant forward power control in a third preset time period. According to the method, the multiple control stages are intelligently divided in the starting stage of the single pulse, different control strategies are adopted, rapid and overshoot-free climbing of the power is achieved, the accuracy and stability of power control are ensured in the different stages, and therefore the overall performance of the pulse radio frequency technology is improved.

Description

Technical Field

[0001] This invention relates to the field of radio frequency power supply technology, specifically to a pulsed radio frequency power supply for semiconductor processes, and particularly to a power segment control method and system for a pulsed radio frequency power supply. Background Technology

[0002] Pulsed RF power supplies are increasingly widely used in advanced semiconductor manufacturing due to their advantages such as effectively reducing process thermal load and improving process uniformity. In pulsed mode, RF power supplies need to complete power ramp-up, stabilization, and shutdown within an extremely short time (microseconds to milliseconds), which places extremely high demands on the dynamic response and stability of the control system. Furthermore, a long-standing technical challenge in pulsed RF processes is the reliable ignition of plasma during the pulse initiation phase. Because the load impedance changes drastically before and after ignition, traditional closed-loop control strategies (whether in constant forward power mode or constant load power mode) have inherent delays in response, easily leading to severe initial power overshoot or oscillation. This instability not only prolongs the power stabilization time but may also interfere with or even kill the formation of the initial plasma seed, causing ignition delay, instability, or even failure. Especially in high-frequency, short-pulse-width applications, the ignition process occupies a large proportion of the entire effective pulse time, and ignition problems directly lead to low process efficiency and non-reproducible results. Therefore, there is an urgent need for an RF power control method that can specifically optimize the pulse initiation phase and ensure rapid, reliable, and stable plasma ignition. Summary of the Invention

[0003] To address the problems of unreliable ignition, initial power overshoot, or oscillation in radio frequency power control systems in the background art, this invention aims to provide a power segment control method and system for pulsed radio frequency power supplies. By intelligently dividing the ignition phase of a single pulse into multiple control stages and employing different control strategies, this invention achieves rapid, overshoot-free power ramp-up and ensures the accuracy and stability of power control at different stages, thereby improving the overall performance of pulsed radio frequency processes.

[0004] To achieve the above-mentioned objectives, the embodiments of the present invention provide the following technical solutions: A power segment control method for a pulsed radio frequency (RF) power supply is disclosed. The pulsed RF power supply generates a pulsed RF signal with power segments. The control unit divides each power segment of the pulsed RF signal into three control stages executed sequentially in time. The control stages include the following steps: S1, using open-loop fixed gain drive, the drive gain of the RF amplifier is fixed at a first threshold value for a first preset time period; S2, a closed-loop control loop is started, and the real-time detected load power is continuously compared with the load power setpoint for a second preset time period, maintaining a constant load power output until the current reflection coefficient is less than the second threshold value or the second preset time period ends; S3, for a third preset time period, the constant target of the closed-loop control loop is switched to forward power, and the real-time detected forward power is continuously compared with the forward power setpoint, maintaining a constant forward power output.

[0005] The invention implements phased control of the power segment. In the first control stage, an open-loop fixed-gain drive is used to avoid power overshoot and oscillation at the pulse start moment, achieving a smooth and rapid power ramp-up. In the second control stage, a constant load power is used for precise power supply. In the third control stage, a constant forward power is used to effectively improve the overall efficiency of the power supply system and make the power supply system more stable, creating conditions for the smooth turn-off of the pulse radio frequency signal.

[0006] Furthermore, in S1, the first threshold is the final drive value at the end of the previous cycle of the corresponding power segment, or is fixed as an initial value preset based on historical data; the first preset time is 5%-20% of the pulse width of the corresponding power segment.

[0007] In the first stage, an open-loop fixed-gain drive is employed, with the fixed drive value being the final drive value from the third control stage at the end of the previous cycle. When there is no previous cycle, i.e., the current cycle is the first cycle, the fixed gain is 0. The primary function of the first control stage is to provide a stable and undisturbed radio frequency electric field environment for gas ionization. This gently rising electric field allows electrons within the cavity sufficient time to be accelerated and gain energy, thereby generating more electrons and ions through collisional ionization. The fixed drive gain avoids drastic power fluctuations, creating a stable "breeding ground" for plasma seed formation.

[0008] Furthermore, the pulsed radio frequency power supply also includes a sensor that continuously detects the forward power and reflected power output by the pulsed radio frequency power supply and transmits the forward power and reflected power to the control unit.

[0009] The sensor is used to detect the output power of the power system in real time, and works with PID to achieve constant load power control and constant forward power control in the second and third control stages.

[0010] Furthermore, in S2, the control unit calculates the real-time detected load power based on the forward power and the reflected power, and compares the load power with the load power set value. If the load power is greater than the load power set value, the drive gain of the RF amplifier is reduced; if the load power is less than the load power set value, the drive gain of the RF amplifier is increased; until the load power is equal to the load power set value.

[0011] In the second stage, constant load power control is used, mainly to ensure "precise energy injection" to complete ignition. This control stage is used to ensure that sufficient and stable energy is continuously coupled into the gas to complete the final avalanche breakdown.

[0012] Furthermore, in S2, the control unit calculates the reflection coefficient based on the forward power and the reflected power. When the reflection coefficient is less than or equal to the set second threshold, the second stage ends prematurely.

[0013] When the plasma begins to form, the load impedance will start to decrease, and the reflected power will decrease. Using the reflection coefficient as a control condition to end the second stage early can be matched with the load state to achieve precise energy coupling control.

[0014] Furthermore, in S3, the control unit continuously compares the real-time detected forward power with the forward power set value. If the forward power is greater than the forward power set value, the drive gain of the RF amplifier is reduced; if the forward power is less than the forward power set value, the drive gain of the RF amplifier is increased; until the forward power is equal to the forward power set value.

[0015] In the third control stage, constant forward power control is adopted to ensure a more stable operating state of the power supply system and to create conditions for the smooth turn-off of the pulse radio frequency signal.

[0016] Furthermore, the sum of the first preset time period, the second preset time period, and the third preset time period is equal to the pulse width time of the corresponding power segment.

[0017] The duration of a single power segment is divided into three preset time periods, and different control steps are used in different preset time periods. This not only enables precise energy control for complex pulses, but also ensures that the control process is orderly and stable.

[0018] Furthermore, the control unit is equipped with a state machine that automatically switches between three control stages based on pulse enable signals and an internal timer.

[0019] The control unit has a built-in state machine that starts counting based on the rising edge of the pulse enable signal and enters the first control stage. After counting is completed in the first control stage, it enters the second control stage. After the calculation is completed in the second control stage or when the reflection coefficient is less than or equal to the second threshold, it enters the third control stage. After counting is completed in the third control stage, the count is reset to zero to prepare for the control of the next pulse radio frequency signal. This achieves automatic and orderly switching of the control unit in the three control stages, ensuring the smooth operation of the control process.

[0020] Furthermore, the present invention also provides a power segment control system for a pulsed radio frequency power supply, used to implement the above-described power segment control method for a pulsed radio frequency power supply. The power segment control system includes a radio frequency generator, a radio frequency amplifier, a sensor, and a control unit; the radio frequency generator and the radio frequency amplifier are used to generate pulsed radio frequency signals with power segments, the sensor is used to detect the forward power and reflected power of the pulsed radio frequency signals, and the control unit is used to divide each power segment of the pulsed radio frequency signals into three control stages executed sequentially in time.

[0021] The present invention has at least the following beneficial effects: 1. The open-loop fixed gain drive in the first stage effectively avoids power overshoot and oscillation at the pulse start moment, and achieves smooth and rapid power build-up.

[0022] 2. The constant load power control in the second stage directly uses the effective power coupled to the process cavity as the control target, which ensures the accuracy and repeatability of the process input energy and improves the process quality.

[0023] 3. The constant forward power control in the third stage optimizes the system operating point during the process stabilization period, improves energy utilization efficiency, and makes the system operation more stable.

[0024] 4. The multi-stage control strategy automatically adapts to different dynamic characteristics during pulse start-up overshoot, taking into account response speed, control accuracy and system stability, and is suitable for complex actual process loads. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a structural block diagram of a pulse radio frequency power supply multi-segment power control system according to an embodiment of the present invention.

[0027] Figure 2This is a schematic diagram of a four-level pulse radio frequency signal according to an embodiment of the present invention.

[0028] Figure 3 This is a schematic diagram of the power waveforms at each stage of a single-stage pulse, representing an embodiment of the present invention.

[0029] Figure 4 This is a control flowchart of the control unit state machine according to an embodiment of the present invention.

[0030] in: 100—RF power supply; 200—Matching unit; 300—Load; 110—RF generator; 120—RF amplifier; 130—sensor; 140—control unit; 150—User communication unit. Detailed Implementation

[0031] 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] In the first embodiment, the present invention provides a single-stage pulse control system for a pulsed radio frequency power supply, as follows: Figure 1 As shown, the pulsed radio frequency power supply 100 includes a radio frequency generator 110, a radio frequency amplifier 120, a sensor 130, a control unit 140, and a user communication unit 150. The radio frequency generator 110 generates pulsed radio frequency signals. The radio frequency amplifier amplifies the pulsed radio frequency signals generated by the radio frequency generator 110 and outputs them to a matching unit 200. After impedance matching by the matching unit 200, the signals are transmitted to the load 300. The sensor 130 detects forward power and reflected power and transmits them to the control unit 140. The control unit 140 receives the forward power and reflected power and controls the radio frequency power supply to output power. The user communication unit 150 receives control commands set by the user.

[0033] The pulsed radio frequency power supply 100 generates pulsed radio frequency signals to the matching unit 200 and the load 300. Figure 2Taking the multi-stage pulse radio frequency signal shown as an example, one pulse period of this multi-stage pulse radio frequency signal contains four power segments with different power levels. The inventive concept of this invention lies in dividing each power segment into three stages for control, as shown in the power waveform. Figure 3 As shown. In Figure 3 In the diagram, T0 represents the duration of a single power segment, which is usually calculated from the pulse frequency and duty cycle set by the host computer. T1 represents the duration of the first stage, T2 represents the duration of the second stage, and T3 represents the duration of the third stage. The solid line represents the forward power curve, and the dashed line represents the reflected power curve.

[0034] Before the first phase begins, the control unit 140 receives a pulse enable signal, pulse width information, load power setting value, and forward power setting value from the user communication unit 150. The control unit 140 controls the RF generator 110 and RF amplifier 120 to generate pulse RF signals accordingly. When the rising edge of the pulse arrives, the control unit enters the first control phase.

[0035] During the first control phase, such as Figure 3 As shown in the T1 time period. The first control stage is the open-loop power ramp-up stage. The goal of this stage is not to quickly reach the power setpoint, but to provide a stable and undisturbed radio frequency electric field environment for gas ionization, so that the electrons in the cavity have enough time to be accelerated and gain energy.

[0036] In the first control phase, the closed-loop control loop is frozen. The control unit no longer performs closed-loop calculations based on real-time power detection values, but instead adopts a fixed-gain power drive method. In this control phase, the control unit sets the drive gain of the RF amplifier to a first threshold value. The first threshold value is the final drive value at the end of the previous pulse cycle of the corresponding power segment. The corresponding power segment refers to the power segment with the same power level and duration in the previous cycle; when the power segment is the power segment of the first cycle, the first threshold value is 0. The duration of the first control phase can be 5%-20% of the pulse width of the entire power segment, or it can be set to a fixed time period.

[0037] The first control stage mainly utilizes system inertia to achieve a rapid and smooth initial power ramp-up, avoiding initial overshoot caused by closed-loop response lag or integral saturation.

[0038] After the first control phase ends, the second control phase begins, such as... Figure 3As shown in T2. ​​The second stage is the constant load power closed-loop stage. The purpose of this stage is to ensure "precise energy injection" to complete the ignition. When the power gently climbs to near the set value and the gas has entered the pre-ionization state, the control target switches to the load power. This is the most critical requirement in the ignition process, ensuring that sufficient and stable energy is continuously coupled into the gas to complete the final avalanche breakdown.

[0039] In the second control phase, closed-loop control is activated, with the control objective being "constant load power." At this stage, sensors continuously monitor forward and reflected power and transmit this data back to the control unit. The control unit calculates the load power based on these figures: Load Power = Forward Power - Reflected Power. The control unit compares the calculated load power with the set load power value. If the load power exceeds the set value, the drive gain of the RF amplifier is reduced; if the load power is less than the set value, the drive gain is increased; and if the load power equals the set value, the current drive gain is maintained for output. It's important to note that increasing or decreasing the RF amplifier's drive gain is achieved by increasing or decreasing the forward power, thereby altering the load power to reach and stabilize at the set load power value.

[0040] In the second control phase, its duration is a certain point before the end of the pulse width of the current power segment. This duration can be modified according to the specific process recipe requirements until the third phase begins. Alternatively, the second control phase ends when the current reflection coefficient is less than the second threshold. In the second control phase, after receiving the forward and reflected power, the control unit simultaneously calculates the reflection coefficient. When the reflection coefficient is greater than the second threshold, the second control phase continues; when the reflection coefficient is less than or equal to the second threshold, the second control phase ends prematurely, and the third control phase begins.

[0041] The second control stage is mainly used to ensure that the energy actually coupled to the plasma is precisely controllable, and is especially suitable for scenarios with strict requirements on process energy input.

[0042] After the second control phase ends, the third control phase begins, such as... Figure 3 As shown in T3. In the second control phase, as the plasma begins to form, the load impedance starts to decrease, and the reflected power reduces. The control unit detects insufficient load power and automatically and smoothly increases the forward power output. This increased energy is efficiently used to support further plasma development and stabilization. Once the plasma stabilizes, the system switches to the third control phase, employing a constant forward power mode, allowing for a seamless switching process and replenishing the final energy gap.

[0043] In the third control phase, closed-loop control is activated, and the control objective is "constant forward power". The sensor detects forward power and reflected power in real time and transmits them back to the control unit. The control unit compares the forward power with the forward power setpoint. When the forward power is greater than the forward power setpoint, the drive gain of the RF amplifier is reduced; when the forward power is less than the forward power setpoint, the drive gain of the RF amplifier is increased; when the forward power equals the forward power setpoint, the current drive gain is maintained for output.

[0044] The duration of the third control stage can be set according to the specific process formula, such as setting it to 30% of the pulse time of the corresponding power segment, until the power segment ends.

[0045] The third control stage is to switch to controlling the forward power after the load plasma has stabilized. This control method can effectively improve the overall efficiency of the power supply system and make the system operation more stable, creating conditions for the smooth turn-off of the pulse.

[0046] The second embodiment further supplements the first embodiment by describing the power segment control method and power segment control system of this invention in detail. The switching process of the three control stages in the power segment control method is as follows: Figure 4 As shown.

[0047] exist Figure 4 In this system, the control unit has a built-in state machine that automatically switches between three control stages based on a pulse enable signal and an internal timer. When the rising edge of the pulse arrives, the internal timer starts counting, and the system enters the first control stage. When the count reaches the switching value for the second control stage, the first control stage ends, and the system enters the second control stage. In the second control stage, when the reflection coefficient is less than a second threshold or the count reaches the switching value for the third control stage, the second control stage ends, and the system enters the third control stage. When the pulse power segment ends, the third control stage ends, the count is reset to zero, and the system enters the starting stage of the next power segment, repeating the above switching process.

[0048] In existing technologies, a single control strategy, such as constant forward power or constant load power, is used throughout the entire pulse start-up period, which cannot simultaneously achieve multiple objectives such as rapid start-up, stable control, and optimal efficiency. In this invention, by intelligently dividing a single pulse power segment into multiple control stages and employing different control strategies, rapid power ramp-up without overshoot is achieved, and the accuracy and stability of power control are ensured at different stages, thereby improving the overall performance of the pulse RF process.

[0049] The third embodiment further describes the power segment control process based on the first and second embodiments. In this embodiment, the control unit adopts a digital controller, such as an FPGA or a high-performance DSP, and the user communication unit adopts a host computer. The digital controller first receives the pulse enable signal, pulse width information, load power setting value, and forward power setting value sent by the host computer. Then, it controls the RF generator and RF amplifier to generate corresponding pulse RF signals.

[0050] When the rising edge of the pulse enable signal arrives, the digital controller enters the first control phase. The digital controller immediately freezes the closed-loop integrators such as the PID controller and locks the control output value to a stored fixed value. This fixed value can be the "final drive value at the end of the previous cycle of the corresponding power segment," or a safety threshold from the previous several stable cycles. This safety threshold is calculated by moving average or filtering based on the stable drive values ​​of multiple pulses within historical cycles to enhance adaptability. This fixed value is converted by a digital-to-analog converter to drive the power amplifier, enabling the RF power to begin output.

[0051] When the timer for the first control phase expires, the digital controller enters the second control phase. The digital controller unfreezes the closed-loop and switches the control target to load power. The PID controller starts working, using its integrator and proportional term to adjust the deviation of the load power, dynamically adjusting the drive gain so that the measured load power quickly tracks and stabilizes at the load power setpoint.

[0052] If the reflection coefficient is less than the second set threshold when the timer for the second control phase expires, or before the timer expires, the digital controller enters the third control phase. The digital controller switches the control target to forward power. The PID controller adjusts the deviation of the forward power to ensure the entire system operates stably at the forward power setpoint. When the falling edge of the pulse enable signal arrives, the digital controller smoothly shuts off the output and saves the current drive value for the first control phase of the next corresponding power segment pulse.

[0053] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of power segment control for a pulsed radio frequency power supply, the method comprising: determining a power segment of the pulsed radio frequency power supply; and controlling the power segment of the pulsed radio frequency power supply. The pulse radio frequency power supply generates a pulse radio frequency signal with at least one power segment, and a control unit divides each power segment of the pulse radio frequency signal into three control stages executed in time sequence; the control stages include the following steps: S1, using open-loop fixed gain driving, fixing the driving gain of the radio frequency amplifier as a first threshold value in a first preset time period; S2, starting a closed-loop control loop, continuously comparing the real-time detected load power with a load power set value in a second preset time period, and dynamically adjusting the driving gain to maintain constant load power output until the current reflection coefficient is less than a second threshold value or the second preset time period ends; S3, in a third preset time period, the constant target of the closed-loop control loop is switched to forward power, and the real-time detected forward power is continuously compared with a forward power set value to maintain constant forward power output.

2. The method of claim 1, wherein, In S1, the first threshold value is the final driving value at the end of the last period of the corresponding power segment; and the first preset time is 5%-20% of the pulse width time of the corresponding power segment.

3. The method of claim 1, wherein the power segment of the pulsed RF power source is controlled by, The pulse radio frequency power supply further comprises a sensor that continuously detects the forward power and reflected power output by the pulse radio frequency power supply and transmits the forward power and reflected power to the control unit.

4. The method of claim 3, wherein the power segment of the pulsed RF power source is controlled by, In S2, the control unit calculates the load power according to the forward power and reflected power, and compares the load power with the load power set value; if the load power is greater than the load power set value, the driving gain of the radio frequency amplifier is reduced; if the load power is less than the load power set value, the driving gain of the radio frequency amplifier is increased; until the load power is equal to the load power set value.

5. The method of claim 4, wherein the power segment of the pulsed RF power source is controlled by, In S2, the control unit calculates the reflection coefficient according to the forward power and reflected power, and ends the second stage early when the reflection coefficient is less than or equal to the set second threshold value.

6. The method of claim 3, wherein the power segment of the pulsed RF power source is controlled by, In S3, the control unit continuously compares the real-time detected forward power with the forward power set value; if the forward power is greater than the forward power set value, the driving gain of the radio frequency amplifier is reduced; if the forward power is less than the forward power set value, the driving gain of the radio frequency amplifier is increased; until the forward power is equal to the forward power set value.

7. The method of claim 1, wherein the power segment of the pulsed RF power source is controlled by, The sum of the first preset time period, the second preset time period and the third preset time period is equal to the pulse width time of the corresponding power segment.

8. The method of claim 1, wherein, The control unit automatically switches between the three control stages according to the pulse enable signal and the internal timer.

9. A power segment control system for a pulsed radio frequency power supply, characterized by, A power segment control method for the pulse radio frequency power supply of any one of claims 1-8.

10. The power stage control system of a pulsed RF power supply of claim 9, wherein, The pulse radio frequency power supply comprises a radio frequency generator, a radio frequency amplifier, a sensor and a control unit; the radio frequency generator and the radio frequency amplifier are used to generate a pulse radio frequency signal with power segments, the sensor is used to detect the forward power and reflected power of the pulse radio frequency signal, and the control unit is used to divide each power segment of the pulse radio frequency signal into three control stages executed in time sequence.

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