Pulsed Bias Plasma Etching of SiN/SiO2 Stacks Without Pattern Deformation

The patent applies periodic pulsed DC bias voltage instead of continuous DC bias voltage. The bias voltage is applied in pulses with specific duty ratios (e.g., 10% to 50%), where the pulse width is controlled to be 0.5 microseconds or less. This periodic application allows ions to be accelerated toward the substrate during the on-period, maintaining high etching speed, while the off-period prevents excessive ion bombardment that would cause pattern collapse or shape abnormalities. The pulsed nature of the bias voltage resolves the contradiction by enabling fast etching without the harmful effects of continuous high-voltage application.

The patent changes the bias voltage parameter to achieve different etching rates for silicon nitride and silicon oxide films. Specifically, a first bias voltage (e.g., 500V to 2000V) is applied during hydrofluorocarbon-based plasma etching of silicon nitride, while a second bias voltage (e.g., 1000V to 3000V) is applied during fluorocarbon-based plasma etching of silicon oxide. This parameter change enables selective etching of the two materials. The complexity is managed by automatically switching between voltage levels based on the etching stage, and by controlling the pulse width to be 0.5 microseconds or less, which simplifies the timing control while maintaining selectivity.