Hybrid clean approach for post-copper CMP defect reduction

A “hybrid” post-Cu CMP cleaning process that combines acidic and basic cleans in sequence is developed and implemented. The new process demonstrates the advantages of both acidic and basic cleans and achieves a more than 60% reduction in CMP defects, such as polish residues, foreign materials, slurry abrasives, scratches, and hollow metal, relative to an all-basic brush clean process. It also eliminates the circular ring defects that occur intermittently during roller brush clean. TXRF scans confirm the reduction of AlO_x defects when using the hybrid clean process. XPS spectra show similar Cu surface oxidation states between the basic and hybrid clean processes. Both short and open yields can be improved by using the new clean process. The underlying mechanism of the huge defect reduction benefits is discussed.