Optimization and mechanism investigation of pulse etching modes for aluminum line patterning in CMOS image sensor chip manufacturing

In semiconductor manufacturing, nonuniform pattern density leads to etch rate variations, which compromise the consistency of metal interconnects and increase risks of signal cross talk or propagation delay. This study systematically investigates aluminum line etching characteristics under varying pattern densities using Cl2/BCl3/N2 inductively coupled plasma with continuous wave (CW) and pulsed modes (including bias, synchronous, and asynchronous pulsing modes). Through parametric optimization of duty cycles and synchronization strategies, critical etching parameters—profile angle, selectivity, and loading effect—were effectively controlled. Compared to the CW mode, bias-pulsed etching enabled tunable profile angles (isolated areas) and selectivity via duty cycle modulation. Synchronous pulsing reduced the loading effect by 54%, while asynchronous pulsing enhanced etch selectivity to photoresist by over 2.3 times. Mechanistic analysis attributes the improved selectivity in pulsed modes to reduce photoresist erosion without affecting aluminum etch rate. Enhanced profile control and loading mitigation correlate with modulated polymer or by-product deposition at pattern sidewalls and bottoms. These findings demonstrate that pulsed plasma strategies optimize critical dimension aluminum line etching while mitigating pattern-density-induced defects, offering a viable pathway for high-density CMOS image sensor chip manufacturing.