POST-CMP CLEANING APPLICATIONS: CHALLENGES AND OPPORTUNITIES

摘要

CMP process detectivity and yield performance depends on effectiveness of the post-CMP (PCMP) cleaning process which should reduce roughness of the polished wafer and leave it defect-free, consistently removing, organic residues, and ionic contamination. This paper presents an overview of PCMP wafer cleaning attributes, trends, challenges and opportunities. PCMP cleaning effectiveness depends on the stability of brush PVA (Poly Vinyl Alcohol) properties, magnitude of brush-wafer frictional force, and the adhesion forces between the particle and wafer, and the particle and brush. Recently developed molded-through-the-core (MTTC) PVA roller brush design with an integral/disposable core provides positive anchoring and adhesion of PVA with the core and excellent dimensional stability, eliminating any possibility of PVA slippage at the core interface unlike slip-on-the-core (SOTC) brushes. Stable behavior of brush-wafer contact-pressure, contact-area, and dynamic-friction could be useful indicators of PCMP cleaning effectiveness and mechanical consistency of brushes over lifetime. Data from tribological studies using a new benchtop tribology tester developed for PVA brushes and a 200 mm wafer test tribometer (accelerated 48 hour tribological stress evaluation) are presented. In addition, results of comparative PCMP cleaning effectiveness fab evaluation of PVA brushes, involving MTTC and SOTC brushes, under brush break-in, scrub only and PCMP cleaning cycles, after Cu/Low-k barrier step CMP process in a 90 nm production fab using 200 mm wafers (blanket and 180 nm feature MIT854 patterned on Mirra Mesa tool) are also discussed. This study highlights the importance of PCMP clean brush design and methods of tribological and PCMP cleaning evaluations to ensure consistent frictiona! characteristics and wafer cleaning performance over brush lifetime, and demonstrates the benefits of using MTTC design PVA brushes in the Cu/low-k PCMP cleaning applications.