In advanced BEOL process, metal defect reduction plays an important role for Cp yield improvement. "Crown defect" is one of the killer defects. It develops in Litho process, forms after Aluminum etching, and finally turns out to be ring-type Al2O3 residue. Aluminum grain size is strongly related with crown defect performance. Especially for thick Aluminum film (>3μm), which is widely applied on high voltage power management IC product, it is a big challenge to control grain size and keep a relatively uniform film surface. In this paper, a study of the relationship between Aluminum grain size and crown defect is presented. Also, a novel approach to control the grain size is shown to reduce the crown defect for Cp yield improvement.