Key Technologies for Repetition Rate Control in Excimer Laser High-Voltage Power Supplies

1. Technical Challenges at High Repetition Rates
Excimer lasers (e.g., ArF, KrF) require kHz-level high repetition rates (typically 4–6 kHz) for applications like semiconductor lithography and precision micro-machining. Under such conditions, traditional thyratron switches face lifespan limitations (only ~10^9 pulses), while voltage fluctuations (10–14 kV) and gas degradation cause pulse energy drift (±15%) and repetition rate instability. For example, declining fluorine concentration in the discharge chamber reduces energy output over time, necessitating real-time voltage compensation. 
2. All-Solid-State Pulsed Power Technology (SSPPM)
To address thyratron limitations, modern systems employ all-solid-state pulsed power modules (SSPPM) with multi-stage magnetic pulse compression: 
• Solid-State Switches: Power semiconductor switches (e.g., IGBTs) combined with magnetic compression circuits compress microsecond discharges into nanosecond fast-rising pulses (<100 ns rise time), enabling kHz operation without degradation. 
• High-Voltage Precision Control: Adjusting the reference voltage of DC power supplies or resonant capacitor voltages enables real-time compensation for gas aging, maintaining energy stability. 
Experiments show SSPPM achieves ±1% pulse energy stability at 300 Hz–6 kHz repetition rates. 
3. Closed-Loop Control and Advanced Algorithms
Energy stability relies on real-time feedback control: 
1. Pulse Energy Monitoring: Pyroelectric detectors or photodiodes capture per-pulse energy data for processing. 
2. Proportional-Integral (PI) Algorithm: Dynamically calculates voltage compensation based on energy error: 
   V_{adj} = K_p \cdot E_{err} + K_i \int E_{err} dt 
   where E_{err} is the deviation from the target energy. Simulations confirm 99.5% energy stability with PI control. 
3. Coarse-Fine Dual-Mode Adjustment: 
   • Coarse Tracking: Stepper motors adjust cavity length for large frequency drifts; 
   • Fine Tuning: Piezoelectric ceramics (PZT) modulate mirror positions (µm precision) for mHz-level frequency locking. 
4. Multi-Parameter Synergistic Optimization
Repetition rate control requires coordination with gas management and wavelength stability: 
• Extended Gas Lifespan: Real-time fluorine monitoring and replenishment, combined with voltage adjustment, extend gas replacement intervals from 3 to 15 days (up to 10^9 pulses). 
• Wavelength-Frequency Coordination: Dynamic waveform adjustment via lookup tables or iterative learning control (ILC) ensures spectral stability during repetition rate shifts, critical for lithography resolution. For example, zero-crossing switching of wavelength waveforms in dual-color modes maintains consistent exposure depth. 
5. Future Directions
Emerging innovations include: 
1. Predictive Control: Deep learning models forecasting gas decay to optimize PI parameters adaptively; 
2. Multi-Module Power Combining: SSPPM parallelization enables kW-level outputs (e.g., 3.6 kW for annealing); 
3. Enhanced Environmental Robustness: Anti-interference designs (e.g., acoustic shock suppression) for complex industrial environments. 
Conclusion
High-repetition-rate excimer laser power supplies are pivotal for lithography precision and efficiency. SSPPM technology overcomes lifespan barriers, closed-loop algorithms ensure microsecond response, and multi-parameter strategies drive advancements in longevity and intelligence. As semiconductor nodes continue to shrink, repetition rate control will underpin the next phase of Moore’s Law.