anisotropic etch

Anisotropic etching creates vertical sidewall profiles with minimal lateral etching, essential for high-resolution pattern transfer in semiconductor manufacturing. Plasma-based reactive ion etching (RIE) achieves anisotropy through directional ion bombardment that enhances vertical etching while sidewall passivation protects lateral surfaces. The ion energy and directionality come from the plasma sheath electric field that accelerates ions perpendicular to the wafer surface. Passivating polymers deposited from fluorocarbon gases protect sidewalls while the bottom surface is continuously cleared by ion bombardment. Anisotropic etching enables high aspect ratio features with straight sidewalls critical for sub-100nm patterning. Process parameters including pressure (low pressure increases anisotropy), RF power, and gas chemistry must be carefully optimized. Aspect ratio dependent etching (ARDE) causes etch rate to decrease in high aspect ratio features, requiring compensation through process tuning or multi-step etch sequences.