160 kV Ultra-Low Ripple High-Voltage Power Supply for Electron-Beam Lithography Systems
Writing features below 3 nm with electron-beam lithography requires the accelerating voltage to remain stable to better than 0.5 ppm over the entire exposure frame and exhibit ripple below 2 V peak-to-peak at 160 kV, otherwise chromatic aberration and stochastic blur destroy critical-dimension control. Achieving this level of performance demands a cascade of mutually reinforcing stabilization techniques that address every known noise source from line-frequency modulation to mechanical microphonics.
The generator topology combines a low-frequency precision rectifier feeding a 35 kHz parallel-fed Cockcroft-Walton multiplier immersed in pressurized SF6. The rectifier itself uses a phase-locked resonant converter locked to a temperature-compensated crystal oscillator, delivering an intermediate 20 kV rail with less than 300 mV ripple. A subsequent active filter stage comprising a high-voltage MOSFET linear regulator in series with the multiplier input cancels residual 700 Hz modulation to below 40 mV before multiplication.
Ripple at the final 160 kV terminal is attacked on three fronts simultaneously. First, the parallel-fed multiplier inherently produces only high-frequency ripple components proportional to drive frequency; second, a distributed RC filter network using vacuum-grade polypropylene capacitors with near-zero voltage coefficient suppresses components above 50 kHz by more than 60 dB; third, an active ripple-cancellation injector consisting of a 2 kV linear amplifier driven from a capacitive pickup at the column entrance injects counter-phase current with 180 dB loop gain at line-related frequencies. Measured ripple routinely falls below 1.1 V p-p across the full 50–500 µA beam-current range.
Long-term stability relies on a compensated resistive divider constructed from bulk-metal-foil resistors selected for matched TCR and VCR, housed in a triple-shielded, oil-filled, temperature-controlled enclosure maintained at 35.000 ± 0.005 °C. Feedback is digitized by a 24-bit sigma-delta converter sampling at 200 kS/s, processed through a digital PID with adaptive integral wind-up protection, and finally converted back to an analog correction signal that drives the series linear regulator. Hour-to-hour drift after 48-hour warm-up remains under 0.4 ppm.
Mechanical vibration isolation uses a two-stage platform: the entire high-voltage tank sits on a passive air-table that attenuates floor motion above 3 Hz, while the multiplier column itself is suspended on carbon-fiber struts pre-stressed to cancel thermal expansion mismatch with the ceramic rings. Acoustic noise from oil-circulation pumps is reduced below 25 dB(A) through remote mounting and anechoic ducting, eliminating detectable microphonic modulation.
Cable-induced noise is suppressed by using specially developed low-triboelectric coaxial cable with a graphite-impregnated dielectric layer and an actively driven guard shield that follows the column potential within 3 V. Charge generation during 600 mm/s stage motion is thereby held below 800 mV.
In-situ calibration occurs automatically every 2000 hours: a precision current source injects known test currents through calibrated shunt resistors at the terminal, and the control loop adjusts digital gain and offset coefficients to maintain absolute accuracy better than 3 ppm over the system lifetime. These systems consistently deliver 160 kV with 0.37 ppm stability and sub-1.5 V ripple in volume production of 3 nm and sub-3 nm logic masks, enabling single-digit nanometer overlay and line-edge roughness specifications previously considered unattainable.
