etch stop

Etch stop layers are intentionally placed materials that have very low etch rate compared to the target material, providing a stopping point that protects underlying structures from over-etch damage. Common etch stop materials include silicon nitride (stops oxide etch), silicon carbide, and silicon-germanium alloys. The etch stop must have high selectivity (>50:1) to the material being etched while being compatible with subsequent processing. Etch stops enable precise thickness control in chemical-mechanical polishing by providing an endpoint signal. In dual damascene processing, etch stops separate via and trench levels and prevent via etch from penetrating the underlying metal. Optical or electrical endpoint detection monitors when the etch reaches the stop layer. Etch stop layers must be thin enough to not significantly impact device performance but thick enough to provide reliable stopping. Stress from etch stop layers can affect transistor performance, requiring careful material selection and thickness optimization.