reactive ion etch lag

Reactive Ion Etch (RIE) lag is the phenomenon where etch rate decreases in high-aspect-ratio features, essentially synonymous with ARDE. **Terminology**: RIE lag and ARDE describe the same fundamental effect. RIE lag is the older, more colloquial term. **Observation**: Smaller or deeper features etch more slowly than larger or shallower ones during the same process. **Physical basis**: Ion and neutral transport limitations in narrow features. Reduced reactant flux and impeded product removal at high aspect ratios. **Measurement**: Compare etch depth across features of different widths or aspect ratios after fixed etch time. Plot etch rate vs AR. **Magnitude**: Can be 20-50%+ rate reduction for AR > 10:1 vs open-area etch rate. **Impact**: Features clear at different times. Overetch needed for slowest features degrades selectivity and can damage underlying layers. **Applications affected**: Contact/via holes, trenches, 3D NAND channel holes, TSV etching. **Mitigation**: Process optimization - lower pressure, pulsed plasma, optimized gas chemistry. **Inverse RIE lag**: Rare cases where smaller features etch faster due to microloading or localized heating effects. **Process development**: Must characterize RIE lag behavior for each new etch recipe.