320 kV Scanning Deflection High-Voltage Waveform Correction for Ion Implantation

High-dose ion implantation on 300 mm wafers at 320 keV requires electrostatic scanning plates to sweep the beam ±180 mm in both X and Y axes at frequencies up to 1.8 kHz while maintaining deflection waveform linearity better than 0.06 % and settling time under 22 µs to prevent dose non-uniformity from overshoot or ringing.

The deflection supply uses four independent ±18 kV amplifiers, each built as a 280 kHz class-D resonant converter driving a 1:28 ferrite transformer followed by a low-inductance output stage. Waveform fidelity is achieved through digital pre-distortion: a 32-bit processor calculates the exact drive waveform required to cancel measured amplifier and cable transfer function, updating coefficients every 2000 wafers via an automated beam-profile calibration sequence.

Settling time is minimized by active damping networks that inject counter-current pulses during slew-rate limiting transitions, reducing 0.1 %-to-0.1 % settling from 78 µs to 18 µs. Cable-induced distortion is compensated by driving the plates through a 1:1 analog correction transformer wound on high-permeability nanocrystalline core that presents the inverse impedance characteristic of the 28 m high-voltage coaxial cable.

Beam position feedback uses four-quadrant beam current monitors at the wafer plane; deviations >42 µm trigger real-time correction offsets added to the nominal waveform with 3 µs latency, maintaining scan uniformity <0.38 % 1-sigma across full 320 keV phosphorus and boron doses.

Cross-axis coupling is suppressed by orthogonal shielding and active common-mode cancellation that injects opposite-phase current into unused plate pairs, reducing X-to-Y influence below 0.018 %.

Thermal management uses oil-free forced-air cooling with temperature-aware waveform scaling: when amplifier heat-sink temperature exceeds 58 °C, maximum slew rate is automatically reduced by 7 % to protect components while maintaining dose accuracy through proportional scan-speed reduction.

These corrected deflection systems routinely achieve dose uniformity <0.42 % 1-sigma on 300 mm wafers at 320 keV with scan speeds supporting >420 wafers/hour in high-current production implanters.