Application of High-Voltage Power Supplies in Plasma Resonance Suppression for Etching Equipment

Plasma resonance is a common challenge in semiconductor etching processes, primarily caused by impedance mismatch between the radio frequency (RF) power source and the reaction chamber. This mismatch generates standing waves, leading to reflected power surges, plasma density oscillations, and ion energy distribution broadening. These effects result in distorted etch profiles, increased sidewall roughness, and mask damage. High-voltage power supplies, as the energy source for plasma generation, can effectively suppress resonance through multidimensional cooperative control, enhancing process stability. 
1. Physical Mechanism and Hazards of Plasma Resonance
Plasma resonance occurs when the load impedance deviates from the power supply’s characteristic impedance (typically 50 Ω). During high-frequency excitation (>27 MHz), electrons accelerated by the alternating electric field collide with gas molecules, causing ionization. Impedance mismatch reflects energy back to the power supply, forming standing waves. Reflected power reduces energy transmission efficiency (losses up to 30%) and triggers nonlinear oscillations in the plasma sheath. These oscillations broaden ion energy distributions (full width at half maximum >20 eV), dispersing ion incident angles in high-aspect-ratio structures and causing sidewall distortion or bottom perforation. 
2. Dual-Frequency Coupling Technology
A dual-frequency driving architecture decouples ion flux and energy control to suppress resonance: 
• High-Frequency Modulation (60 MHz): An LCC series-parallel resonant topology improves conversion efficiency to 90%. Adaptive pulse width modulation (PWM) dynamically matches plasma impedance. For example, when reflected power exceeds a threshold, the system switches to pulse frequency modulation (PFM) within microseconds, adjusting the switching frequency to compensate for impedance drift and maintaining forward power fluctuations below ±0.5%. 
• Low-Frequency Bias Synchronization (2 MHz): Negative DC bias (e.g., -1.5 kV) is injected during pulse intervals to accelerate electron neutralization of positive charges at the bottom of deep trenches. A key innovation is timing control: bias output is paused for 0.5–2 μs after high-frequency power initiation, allowing the sheath to fully form before applying bias, preventing electrode discharge caused by electron rebound. 
3. Pulse Modulation and Timing Synchronization
Nanosecond-level pulse technology compresses ion energy distributions to suppress resonance: 
• Duty Cycle Optimization: Pulse frequencies of 10–100 kHz with duty cycles of 5–20% are employed. Low duty cycles (5%) limit average electron energy, reducing interference from high-energy electrons on impedance matching networks, while high duty cycles (20%) maintain etch rates. Experiments show that with pulse rise times <50 ns, ion energy distributions can be compressed to below 5 eV, significantly minimizing sidewall erosion. 
• Multistage Protection: Integrated overvoltage/overcurrent/overtemperature protection circuits cut off power and restart matching networks within 10 μs during plasma arcing or abnormal gas ionization. An HSM safety monitoring core pre-diagnoses faults to prevent transient damage. 
4. Intelligent Impedance Matching and Real-Time Compensation
Dynamic impedance matching is central to resonance suppression: 
• Closed-Loop Feedback: A 300 MHz dual-core ARM MCU analyzes forward/reflected power ratios in real time, driving a variable capacitor matrix (5–200 pF) to adjust LC matching networks. For structures with aspect ratios >100:1, capacitor adjustments compensate for sheath capacitance variations, suppressing reflected power below 5% of input power. 
• AI Optimization: Deep learning models trained on plasma emission spectra predict optimal power-frequency-pressure parameter sets. For SiO₂ etching, the model recommends 60 MHz source power at 1.5 kW, 2 MHz bias power at 200 W, and 0.5 Pa pressure, reducing resonance-induced non-uniformity to <2%. 
Conclusion
Suppressing plasma resonance requires dynamic equilibrium between energy transmission and load response. Innovations in high-voltage power supplies—dual-frequency decoupling, pulse modulation, and intelligent matching—have advanced plasma control from macroscopic stability to microscopic precision. Future developments, such as SiC wide-bandgap devices and 3D power topologies, will enhance transient response and energy efficiency, enabling atomic-level etching for sub-3 nm processes.