Electrostatic Chuck Power Supply: Improving Uniformity of Surface Charge Distribution and Consistency of Holding Force

Electrostatic chucks (ESCs) are widely used in semiconductor wafer handling, precision optics, and flat-panel display processing. The uniformity of the surface charge and the consistency of the electrostatic attracting force across the chuck surface are critical to achieving flatness, alignment accuracy, and wafer integrity. The performance of the high-voltage power supply driving the electrostatic chuck strongly influences charge distribution, leakage, and field uniformity. Enhancing these attributes involves careful design of the power architecture, feedback control, and spatial charge compensation strategies.
An effective ESC power supply must deliver a stable, low-noise DC or pulsed high voltage with minimal ripple and drift. Ripple levels should be maintained in the low microvolt or sub-10 µV range, and long-term drift must be corrected via feedback loops. A multi-zone output architecture is advantageous: the chuck electrode is segmented into concentric or grid zones, each powered by an independent output channel. This allows fine adjustment of surface potentials regionally, compensating for nonuniform dielectric thickness, substrate variations, or microfabrication tolerances.
To dynamically correct charge nonuniformities, an array of embedded field sensors (electrostatic or capacitive probes) can measure local surface potential or field gradient. A digital controller compares these sensor readings with the desired uniform potential profile and adjusts individual zone voltages via closed-loop control. The correction algorithm may use proportional-integral-derivative (PID) control or model-based predictive compensation to drive zone voltages until field deviations are minimized (e.g. within ±1 %).
Leakage currents, dielectric inhomogeneities, and edge effects often distort charge distribution. To mitigate these, the power supply implements soft-voltage ramping during charge-up and charge-down phases to avoid dielectric breakdown or localized overcharging. The ramp rate is tuned to the dielectric relaxation time constants of the chuck material. Moreover, periodic “charge equalization pulses” of opposite polarity or lower amplitude may be applied to suppress charge accumulation drifts over time.
Noise suppression is also essential. The power supply integrates multi-stage filters (LC, RC, active filters) and electromagnetic shielding to suppress high-frequency interference that can modulate surface charge. Grounding and isolation design prevent coupling from external equipment. Temperature compensation circuits monitor internal temperature and apply drift correction to voltage references, maintaining stable performance over wafer processing cycles.
In testing, measurement of uniformity may be conducted via electrostatic Kelvin probe mapping or dark-field wafer displacement measurement under vacuum conditions. Results often show that after implementing zoned control and feedback compensation, variance in surface potential is reduced from ±8 V to ±1 V over a 300 mm diameter, and edge-to-center attractive force deviation drops from ±10 % to ±2 %. Thus, a well-designed power supply with zonal output and feedback compensation substantially improves ESC performance, enabling higher yield and wafer protection.