High-Efficiency Soft-Switched Pulsed Plasma Bias Supply System

Abstract

Radio Frequency (RF) generators play a crucial role 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 (kilovolt range), high frequencies (hundreds of kilohertz to low megahertz), precise timing, and broadband frequency content. Traditional methods to generate these waveforms are limited by semiconductor voltage ratings, leading to either low-voltage waveforms or complex circuits to achieve higher pulse voltages. This work presents a simple, compact, and efficient method for generating a pulsed bias voltage for plasma processing. The approach involves synthesizing the pulsed waveform at a low, convenient voltage and then using a transformer to step up the voltage to the desired level. A low-leakage inductance coaxial cable-based transformer is developed to provide scaling with sufficient fidelity across a wide frequency range. Zero voltage switching (ZVS) is achieved on all devices, ensuring highly efficient operation. The proposed system is validated through a lab bench prototype that generates pulses of 2.1 kV at a frequency of 400 kHz. Additionally, this system allows for adjustments in pulse duty ratio and slew rate, offering enhanced control and versatility for various applications.