Precision Synchronization of Pulse Repetition Frequency in Excimer Laser High-Voltage Supplies for Lithography Light Sources
Excimer lasers generate the ultraviolet light for the lithography exposure, and the laser pulses are produced by the discharge of the stored energy through the gas mixture. The high-voltage supply of the excimer laser controls the charging and the discharging of the pulse power system, and the synchronization of the pulse repetition frequency with the other components of the exposure tool determines the stability of the light output. The engineering work covers the timing control, the energy regulation, and the interference management, and the requirements are defined by the lithography process.
The excimer laser operates with the repetitive pulses, and each pulse delivers the energy to the gas mixture through the fast discharge. The high-voltage supply charges the capacitor bank between the pulses, and the charging must be completed within the pulse period. The precision of the pulse timing determines the stability of the laser output, and the synchronization with the scanner movement is essential for the exposure accuracy.
The pulse repetition frequency is set by the exposure requirements, and the supply must maintain the frequency with the high precision. The timing jitter of the pulses affects the exposure uniformity, and the synchronization circuit coordinates the charging, the triggering, and the discharge events. The reference clock of the lithography tool provides the timing base, and the supply synchronizes the pulse generation with the reference.
The energy of each pulse depends on the charging voltage of the capacitor bank, and the energy regulation maintains the pulse energy at the set value. The charging voltage is controlled by the supply, and the measurement of the delivered energy provides the feedback for the regulation. The pulse-to-pulse energy stability is critical for the exposure quality, and the supply is designed for the precise energy control.
The high-voltage discharge generates the electromagnetic interference that can disturb the sensitive electronics of the lithography tool, and the shielding and the filtering are designed to contain the interference. The grounding scheme avoids the coupling of the discharge currents into the control circuits, and the layout of the high-voltage section is optimized for the low inductance. The interference management is verified through the electromagnetic compatibility tests.
The gas mixture of the excimer laser degrades with the operation, and the discharge characteristics change over the gas life. The supply compensates for the gas degradation through the adjustment of the charging voltage, and the gas replacement is scheduled from the monitoring data. The energy output remains within the specification over the gas life, and the process stability is maintained.
The cooling system of the laser removes the heat generated by the discharge and the power electronics, and the temperature stability affects the gas pressure and the discharge behavior. The thermal management maintains the operating temperature within the specified range, and the temperature monitoring supports the protection of the system. The cooling capacity is sized for the maximum repetition rate.
The integration of the supply with the laser system includes the coordination of the trigger signals and the status communication, and the control interface provides the setting and the monitoring of the pulse parameters. The synchronization with the scanner and the other subsystems is verified through the joint testing, and the complete exposure system is qualified for the production.
The reliability of the high-voltage supply is essential for the continuous operation of the lithography tool, and the components are selected for the high duty cycle. The protection circuits respond to the abnormal conditions and the diagnostics support the troubleshooting. The modular design of the supply enables the quick replacement of the faulty units, and the downtime is minimized.
The advanced lithography processes demand the higher repetition rates and the better pulse stability, and the development of the supplies follows the requirements of the new exposure tools. The digital control enables the precise timing and the flexible configuration, and the integration with the tool software improves the operation. The cooperation with the laser and the lithography manufacturers drives the innovation.
Precision synchronization of the pulse repetition frequency in the excimer laser high-voltage supplies ensures the stable light output for the lithography exposure, and the accurate timing, the energy regulation, and the careful interference management deliver the required performance. The continued development will support the advancement of the lithography technology.
The charging topology of the pulse power system determines the efficiency and the charging time, and the resonant charging reduces the losses and the stress on the components. The charging voltage is regulated through the feedback control, and the energy stored in the capacitor bank is delivered to the discharge circuit. The design of the charging stage is optimized for the required repetition rate.
The measurement of the pulse energy provides the data for the process control, and the energy is monitored for each pulse. The variation of the energy is analyzed statistically, and the control loop corrects the drift of the charging voltage. The energy data is recorded for the quality assurance of the exposure process.
The operation of the excimer laser at the high repetition rates requires the careful thermal management, and the heat generated by the discharge and the power electronics is removed by the cooling system. The temperature of the gas and the electrodes affects the discharge stability, and the temperature control maintains the process conditions. The cooling system is monitored for the reliable operation.
The reliability of the pulse power system is verified through the endurance testing, and the test covers the full operating range of the repetition rate and the energy. The component temperatures and the electrical stresses are monitored during the test, and the results are used for the design improvement. The verification supports the qualification for the production use.
The alignment of the laser pulses with the wafer exposure is verified through the joint testing of the laser and the scanner, and the timing errors are measured and corrected. The synchronization accuracy is maintained over the long exposure runs, and the drift of the timing is monitored. The verification data supports the release of the tool for the production, and the periodic checks confirm the continued accuracy.
