Cost-Effective Electrical Variable Capacitor Utilizing Fast Recovery Diode for RF Plasma

As semiconductor technology advances, etching processes demand higher precision and deeper etching depths. Impedance matching networks are employed to improve plasma stability and etching accuracy. Traditionally, Vacuum Variable Capacitors (VVCs) have been used in these networks; however, their mechanically driven operation limits response speed, leading to degraded precision under rapidly changing plasma conditions. To address this limitation, an Electrical Variable Capacitor (EVC) using semiconductor switches such as MOSFETs has been proposed. EVC achieves capacitance tuning speeds over 1,000 times faster than VVC, enabling microsecond-scale control suitable for advanced plasma processes. However, conventional EVC circuits require costly components such as PiN diodes and high-voltage external power supplies, making practical replacement of VVCs difficult. This paper proposes a new EVC topology that eliminates PiN diodes and external power, reducing cost by more than tenfold. Experimental verification confirms that the proposed circuit can effectively replace conventional VVCs in next-generation impedance matching networks.