isotropic etch

Isotropic etch removes material equally in all directions, creating rounded profiles and undercutting. **Mechanism**: Chemical reaction dominates. No directional component. Etch rate same vertically and horizontally. **Wet etch**: Most wet etches are isotropic. HF on oxide, acids on metals. **Undercut**: Lateral etching under the mask. Undercut distance equals vertical etch depth. **Profile**: Rounded edges, bowl shapes for circular openings, tapered sidewalls. **Applications**: **Cleaning**: Remove residues without concern for profile. **Release**: MEMS release etch removes sacrificial layer. **Wet strip**: Remove blanket films or contamination. **Comparison to anisotropic**: Anisotropic maintains mask dimensions. Isotropic is less controlled but simpler. **Selectivity**: Usually high selectivity available (etch target, stop on underlying material). **Uniformity**: Easier to achieve uniform etch with wet isotropic. **Limitations**: Cannot pattern small features due to undercut. Lines would be narrowed or removed. **Historical**: Used more in older technologies before anisotropic plasma etch developed.