Solution of in-line inspection problem for grainy metal layers by "saturation effect" of grayscale

We demonstrate a solution, which enhances the practical sensitivity of in-line pattern matching inspectors for grainy metal layers by reducing the nuisance counts without additional investment. We confirmed that most nuisance defects are caused by the grain boundaries on the Hot-AlCu wirings. Then we proposed a new solution called saturation effect to decrease the defect signals from the grain boundaries. The experimental results prove that the saturation effect with illumination brightness optimization successfully cancels the defect signal from grain boundaries. As a result, we can efficiently detect real defects without detecting the grain boundaries. The observed practical sensitivity limit is enhanced from 0.8 μm to 0.4 μm. We believe this solution may accelerate the yield enhancement counter measurements based on in-line inspection results