射频阻抗自动匹配方法的研究与实现

发布时间：2018-04-13 19:48

本文选题：射频源 + Smith圆图　；参考：《郑州大学》2017年硕士论文

【摘要】：功率射频源在真空镀膜、半导体刻蚀和感应加热等离子体等领域得到了广泛应用。工业上常用的射频源频率为13.56MHz,内阻RS为50Ω。通常负载阻抗不等于射频源内阻,若将射频源和负载直接相连时,会存在不同程度的失配。阻抗失配将导致传输线上存在功率反射,能量不能全部被负载所接收,降低传输效率。若失配程度较深,则会引起加工过程的失败。因此在射频源(或传输线末端)与负载之间需要设置匹配网络。负载阻抗随工作时间和周围环境等因素的变化而在一定范围内变化,只有实时检测负载阻抗的变化并调整匹配网络的参数,才能得到最大传输效率,因此阻抗自动匹配器的研究就显得至关重要。此文根据加工过程中负载变化特点,利用阻抗在Smith圆图上的变化规律,设计Γ型匹配网络,匹配网络由一个微调电感和两个真空可调电容组成。由负载变化范围和工作条件确定匹配网络中的元件参数,设计并制作符合要求的阻抗匹配网络。由于射频源的最大工作电压峰值为200V,最大工作电流峰值为4A,因此利用性能优于传统电流互感器的罗氏线圈实时检测传输线上的电流信号,并根据电路设计需要实现1:10的变比,采样元件分别选用满足自积分条件的电阻与电容。利用电容分压器实时检测传输线上的电压信号并实现1:340的变比,将检测到的电压和电流输入AD8302幅相变换电路得到信号幅度比和相位差,输入STM32,经过模数转换,计算出任意时刻的阻抗,根据Smith圆图的阻抗和导纳的变化特点,采用PID算法控制步进电机的转角,由步进电机带动可调电容的变化,由此形成全新的闭环控制系统。控制目标是使电路在3s内实现匹配,并且使误差控制在5%以内。
[Abstract]:Power RF sources are widely used in vacuum coating, semiconductor etching and inductively heated plasma.The frequency of RF source is 13.56 MHz and the internal resistance RS is 50 惟.Usually, the load impedance is not equal to the internal resistance of the RF source. If the RF source is directly connected to the load, there will be some mismatch.The impedance mismatch will lead to the power reflection on the transmission line, and the energy can not be completely received by the load, which reduces the transmission efficiency.If the mismatch degree is deep, it will cause the failure of the processing process.Therefore, a matching network is required between the RF source (or the end of the transmission line) and the load.The load impedance varies in a certain range with the change of working time and surrounding environment. Only by detecting the load impedance in real time and adjusting the parameters of the matching network can the maximum transmission efficiency be obtained.Therefore, the research of impedance automatic matcher is very important.According to the characteristics of load variation in the process of machining, a 螕 type matching network is designed by using the law of impedance variation on the Smith diagram. The matching network is composed of a fine-tuned inductor and two vacuum tunable capacitors.The component parameters in the matching network are determined by the load variation range and working conditions, and the impedance matching network that meets the requirements is designed and fabricated.Because the maximum operating voltage of RF source is 200V and the maximum working current peak is 4A, the Roche coil, which has better performance than traditional current transformer, is used to detect the current signal on the transmission line in real time, and the 1:10 ratio is realized according to the circuit design.The resistors and capacitors which satisfy the self-integration condition are selected respectively.The voltage signal on transmission line is detected in real time by capacitor divider and the variable ratio of 1: 340 is realized. The detected voltage and current are input into AD8302 amplitude-phase conversion circuit to obtain signal amplitude ratio and phase difference, and STM32 is input to the circuit.The impedance at any time is calculated. According to the characteristic of impedance and admittance of Smith circle diagram, the rotation angle of step motor is controlled by PID algorithm, and the variable of adjustable capacitance is driven by step motor, thus a new closed-loop control system is formed.The control goal is to match the circuit within 3 s and to control the error within 5%.
【学位授予单位】：郑州大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN702

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