Main-Discharge High-Voltage Magnetic Switch Compression for Excimer Lasers

The 308 nm XeCl and 193 nm ArF excimer lasers for lithography and micromachining require main-discharge voltages of 24–34 kV compressed into 110–180 ns pulses with rise times below 48 ns and jitter under 620 ps to achieve stable 15–60 mJ output and dose control better than 0.11 %. Modern magnetic switch compression systems therefore replace thyratron primary switches with all-solid-state magnetic pulse compression networks that deliver greater than 99.9999 % reliability across billions of pulses.

The circuit begins with a 1.2 kV command-charged resonant supply that charges a 38 nF primary capacitor in 3.8 µs. Energy is transferred through three saturable magnetic switch stages using Fe-based nanocrystalline cores with square B-H loops. The first stage compresses from 3.8 µs to 780 ns, the second to 180 ns, and the final stage to 112 ns FWHM while simultaneously stepping voltage up to 32 kV across the laser electrodes.

Pulse-to-pulse repeatability is maintained by active reset of all cores using a 180 kHz bipolar current source that drives each inductor to exactly –1.9 T before every shot. Reset current is servo-controlled from a Hall-effect sensor in the final core, nulling flux drift caused by temperature rise during 8 kHz burst operation. Resulting voltage amplitude stability remains <0.26 % over 120 million pulse gas lives.

Rise-time sharpening in the final stage uses a low-inductance peaking capacitor and adjustable saturable shunt that clips the wavefront at precisely 42 ns 10–90 %. Timing is locked to the pre-ionization corona pulse via a fiber-optic delay generator with 40 ps resolution, maintaining discharge overlap within ±680 ps.

Fluorine compatibility is achieved by full encapsulation of the compression modules in nitrogen-purged aluminum housings with only ceramic and glass-to-metal feedthroughs exposed to the laser chamber. Core cooling uses forced fluorinert flow through PTFE tubing bonded to the core surface, maintaining ΔT <6 °C at 6 kW average power.

Fault tolerance incorporates triple-redundant trigger paths and automatic stage bypass: if the second compression stage saturates early, the control system instantly increases primary charge voltage by 6–9 % to compensate, maintaining output energy within ±0.4 % until scheduled maintenance.

These magnetic compression systems routinely deliver >42 mJ stable output at 8 kHz from ArF lithography lasers with electrode lifetime >38 billion pulses and electrical efficiency >84 %, enabling sustained dose uniformity supporting CD control below 0.72 nm 3-sigma in high-volume 5 nm production.