Metal 1 (M1) Cu deposition represents the first global routing layer in the back-end-of-line (BEOL) interconnect structure A1.Unlike the Metal 0 step, which typically utilizes tungsten or highly stable conductive plugs for local middle-of-line (MOL) contacts, M1 initiates the low-resistance copper dual-damascene scheme A1.Furthermore, compared to the upper Metal 2 through Metal 4 routing layers, M1 exhibits the tightest pitch and smallest critical dimensions, placing the most stringent demands o