trench

A trench is an etched channel in dielectric material that will be filled with conductor (copper) or other material. **In damascene**: Trenches form the horizontal wire paths. Filled with copper and polished back. **Dual damascene**: Via and trench formed together, single metal fill. Efficient process. **Trench dimensions**: Width matches design rules (tens of nm for metal lines). Depth defines wire cross-section. **Aspect ratio**: Depth to width ratio. Higher aspect ratio = more etch and fill challenge. **Etch profile**: Vertical sidewalls critical. Taper causes line-to-line variation. **Trench-first vs via-first**: Order of forming trench and via in dual damascene. Trade-offs in process integration. **STI trench**: Shallow trench isolation - trenches between transistors filled with oxide for isolation. **Fill requirements**: Copper fill must be void-free. Barrier and seed layers before plating. **CD control**: Trench width uniformity affects resistance uniformity. **Dielectric**: Low-k materials make etch and integration more challenging.