Soft-Switched Pulsed Bias Plasma Supply System

Radio Frequency (RF) generators are essential as bias voltage sources in plasma-enhanced semiconductor manufacturing processes. Employing pulsed waveforms to generate plasma offers significant improvements in manufacturing precision. However, producing these waveforms is challenging due to the need for high voltages (in the kV range), high frequencies (hundreds of kHz to low MHz), precise timing, and broadband frequency content. Traditional methods to generate these waveforms are constrained by semiconductor voltage ratings, resulting in either low-voltage outputs or complex circuits to achieve higher pulse voltages. This work introduces a simple and compact method for generating pulsed bias voltages for plasma processing, enabling reduced loss compared to the more complex systems previously described in the literature. The approach synthesizes the pulsed waveform at a low, convenient voltage and then uses an auto-transformer to step up the voltage to the desired level. A coaxial cable-based transformer having low leakage inductance is developed to provide scaling with sufficient fidelity across a wide frequency range. Zero voltage switching (ZVS) is achieved on all devices, ensuring low-loss operation. The proposed system is validated through a lab bench prototype that generates pulses of 2.1 kV at 400 kHz. The proposed system further offers both adjustable pulse duty ratio and slew rate, providing enhanced control and versatility for various applications.