Energy Stability Research of High Voltage Pulsed Power Supply for Deep Ultraviolet Lithography Excimer Laser Light Source
Deep ultraviolet lithography using excimer lasers has become the enabling technology for advanced semiconductor manufacturing. The lithography process requires extremely stable laser output to achieve consistent pattern transfer and high yield. The high voltage pulsed power supply that drives the excimer laser plays a critical role in determining laser energy stability. The research into energy stability of these power supplies requires understanding of laser physics, pulse power technology, and control systems. Achieving the required stability presents significant technical challenges.
The electrical requirements for excimer laser power supplies depend on the specific laser type and lithography requirements. Typical operating voltages range from tens to kilovolts, with pulse energies from millijoules to joules depending on the laser power. The power supply must generate pulses with extremely precise energy control, typically within one percent or better. The load presented by the laser discharge varies with gas composition, pressure, and other factors, requiring the power supply to adapt to these variations while maintaining pulse energy stability.
Excimer laser fundamentals rely on gas discharge physics. The laser gas mixture typically includes a halogen gas such as fluorine or chlorine combined with a noble gas such as argon, krypton, or xenon. High voltage pulses create a discharge that excites the gas molecules, which then emit UV light when they relax. The laser output energy depends on the discharge energy, gas composition, and resonator characteristics. The power supply must provide pulses with consistent energy to maintain stable laser output.
Pulse energy stability is critical for lithography performance. Variations in laser energy cause variations in exposure dose, affecting critical dimension control and pattern fidelity. The power supply must maintain pulse energy stability within tight tolerances across millions of pulses. Stability requirements become more stringent as lithography nodes shrink. The power supply must compensate for various factors that can cause energy variations.
Pulse generation circuitry determines the basic pulse characteristics. The power supply typically uses a pulse forming network or similar circuit to generate the required pulse shape. The pulse forming network components must be precisely matched to achieve the desired pulse characteristics. Variations in component values or switching timing can cause energy variations. The circuit design must be optimized for stability and repeatability.
Charging circuit precision affects pulse energy consistency. The energy stored in the primary capacitor determines the available pulse energy. The charging circuit must charge this capacitor to a precise voltage for each pulse. Charging accuracy, stability, and repeatability directly affect pulse energy stability. Advanced charging circuits may use resonant charging or other techniques to improve precision and efficiency.
Switching system precision is critical for pulse timing and energy transfer. The switching elements must trigger at precisely the right time to ensure consistent energy transfer. Timing jitter and variations in switching characteristics can cause energy variations. The switching system must provide precise control with minimal jitter. Advanced switching may use solid-state devices for improved precision and reliability.
Gas condition monitoring and control are essential for laser stability. The laser gas composition and pressure change over time due to chemical reactions and gas consumption. These changes affect the discharge characteristics and laser output energy. The power supply must adapt to changing gas conditions while maintaining pulse energy stability. Some systems implement feedback control based on laser output measurements to compensate for gas condition changes.
Thermal management affects component stability and performance. The power supply components heat up during operation, causing parameter drifts that can affect pulse energy. Thermal management systems must maintain stable component temperatures to minimize these drifts. The thermal design must consider the duty cycle, ambient conditions, and cooling system capabilities. Temperature compensation may be implemented to correct for thermal effects.
Feedback control systems enhance energy stability. The laser output energy can be measured and used to adjust the power supply parameters. This feedback enables correction for variations in gas conditions, component drifts, and other factors. The feedback loop must be fast enough to correct pulse-to-pulse variations while maintaining stability. Advanced control algorithms may implement predictive control or other sophisticated approaches.
Pulse-to-pulse stability requirements are extremely demanding. The power supply must maintain energy stability from one pulse to the next, not just on average. This requires precise control of all pulse generation parameters. Random variations must be minimized through careful design and component selection. Pulse-to-pulse stability is critical for achieving consistent lithography results.
Long-term stability must be maintained across extended operation. The power supply must maintain stable performance over millions of pulses and hundreds of hours of operation. Component aging, gas consumption, and other factors can cause gradual performance changes. The power supply must compensate for these long-term drifts to maintain consistent laser output. Long-term stability is essential for lithography tool productivity and yield.
Diagnostic capabilities support maintenance and troubleshooting. The power supply should monitor internal parameters to identify developing problems. Diagnostics may include component temperatures, switching characteristics, and charging circuit performance. Advanced diagnostics can predict maintenance needs before failures occur. Diagnostic capabilities help maximize tool uptime and reduce maintenance costs.
Future lithography requirements will demand even greater stability. As lithography nodes continue to shrink, the requirements for energy stability will become more stringent. Power supply technology must continue to advance to meet these requirements. Research into new control techniques, component technologies, and system architectures will be necessary to support future lithography needs.
