Post-CMP Clean PVA Brush Design Advancements and Characterization in Cu/Low-k Applications

Abstract:
The stable behavior of brush-wafer contact-pressure, contact-area, and dynamic-friction could be useful indicators of Post-CMP (PCMP) cleaning and mechanical consistency of PVA (Poly Vinyl Acetal) brushes over lifetime. Newly developed advanced molded-through-the-core (MTTC) PVA brush design with a disposable core and positive anchoring of PVA to the core, eliminates possibility of PVA slippage at the PVA-core interface and results in consistent performance throughout the brush lifetime. PCMP cleaning methods and brush designs are discussed with the evolution of PCMP cleaning chemistries, and the mechanism of the particle removal through brush scrubbing. Accelerated tribological stress evaluation (48 hour marathon run) of PVA brushes employing two slip-on-the-core (SOTC) brushes (A and B) and one MTTC brush (C), demonstrate a very different behavior of waferliquid- brush contact–pressure, contact–area, and dynamic coefficient of friction (COF). Brushes - A and C showed a more consistent behavior of mean COF, whereas design Brush - B experienced catastrophic failure somewhere between 2 and 8 hours. The total variation range of COF for MTTC Brush - C was found to be minimum. In another test, the PCMP cleaning performance of an improved PVA MTTC design brushes was found to be similar or better than the fab POR SOTC design brushes. This study highlights the importance of PCMP clean brush design (chemically, mechanically, and dimensionally), and the methods of tribological and PCMP cleaning evaluations to ensure consistent wafer cleaning performance, throughout the brush lifetime.