E-Chuck Dedicated Reverse-Pulse High-Voltage Circuit for De-Chucking

Rapid and particle-free wafer release from bipolar electrostatic chucks in sub-3 nm etch and deposition tools requires the complete neutralization of stored charge in under 280 ms while limiting residual surface potential to less than ±0.8 V. Dedicated reverse-pulse circuits therefore generate precisely shaped bipolar pulses of ±1200 V at peak currents exceeding 120 A with total delivered energy recovery above 94 %.

The circuit uses a resonant H-bridge of 1.7 kV silicon carbide MOSFETs driving a 1:1 air-core pulse transformer directly coupled to the chuck electrodes through low-inductance vacuum feedthroughs. Energy storage is distributed across twelve 4.7 µF low-ESR film capacitors mounted within 40 mm of the chuck to minimize stray inductance below 18 nH. Discharge begins with a half-sine current pulse of 110–140 A that collapses clamping voltage to near zero in 90–140 µs, followed immediately by a controlled reverse-polarity pulse of 38–52 % amplitude that over-neutralizes remaining dielectric absorption charge.

Pulse shape is actively sculpted by a field-programmable gate array that modulates MOSFET on-time in 8 ns increments based on real-time electrode current measured via coaxial shunts. A learning algorithm executed on every wafer refines the reverse-pulse amplitude and duration using data from the previous 50 cycles, achieving residual charge below 4.2 nC (≈0.6 V surface potential) regardless of chuck age or helium leak rate variation.

Energy recovery occurs through synchronous rectification back to the 400 V intermediate bus during both forward and reverse phases, achieving >96 % efficiency and eliminating the several watts of continuous bleed loss present in resistive discharge designs. Peak power demand from the facility supply is thereby held below 180 W even at 18 wafers per minute.

Multi-zone chucks with up to 28 electrodes are supported by stacking identical pulse modules on a common low-inductance backplane with fiber-optic trigger distribution. Zone timing is staggered by 11 µs to prevent mutual inductive coupling through the wafer silicon, eliminating the 3–7 V rebound previously observed on outer zones.

Arc-free operation during reverse pulse is ensured by pre-bias monitoring: 40 ms before discharge, the circuit measures chuck insulation resistance at 120 V; if resistance falls below 18 GΩ (indicative of polymer bridging), it automatically inserts a 600 V opposite-polarity cleaning pulse before the main de-chuck sequence.

These reverse-pulse circuits routinely achieve full de-chuck in 218–272 ms with final surface potential under ±0.48 V, enabling robot pre-entry speeds above 680 mm/s and contributing to wafer-exchange times below 3.9 seconds in the most aggressive 300 mm etch platforms.