A Breakthrough Method for the Effective Conditioning of PVA Brush Used for Post-CMP Process

Abstract

Polyvinyl acetal (PVA) brush cleaning is one of the most important processes in the post chemical mechanical planarization (CMP) cleaning process. However, PVA brush could be severely contaminated due to strong direct contact with a large amount of abrasive particles during the long-time post CMP cleaning, and the particles on the brush can be easily transported to the next wafer substrate. In this study, we tested four different types of conditioning processes to remove the particles from the brush to increase the cleaning efficiency of post CMP process and comparatively evaluated using FE-SEM. The physical scrubbing method showed higher cleaning efficiency than the chemically dipping method, but some abrasive particles remained on the non-contacted surface. The flow-through method using pH 11 showed the higher removal ability than pH 3 and 7 due to strong repulsive force between silica abrasive particle and PVA brush, but some abrasive particles remained due to non-uniform flow of chemicals. The ultrasonication method with DIW was found to be very effective to remove the particles completely from the brush without damage. Consequently, the new developed conditioning process provides an environmentally friendly and cost effective alternative conditioning process to the existing conditioning process of contaminated PVA brushes.

Inhibition of Silica Nanoparticle Adhesion to Poly(vinyl alcohol) Surfaces by Ammonia-Mediated Hydration: Implications for Effective Post-Chemical–Mechanical Planarization Cleaning

“…These results and arguments are largely consistent with the previous studies on the silica-PVA interactions by zeta potential measurements. 20 However, this mechanism does not explain the significant difference between the NH 3 and KOH solutions. In addition, the strong t d dependence of F ad in the time scale of several seconds cannot be explained only by the electrostatic interactions.…”

“…In the previous studies, scanning electron microscopy (SEM) has been commonly used for imaging nanoparticles adsorbed on a PVA surface. 11,19,20,33 In addition, fluorescence microscopy has been employed for realtime observations of dynamic nanoparticle movements during the PVA brush scrubbing. 33,34 However, these methods do not allow us to directly measure the interaction forces acting between the nanoparticles and the PVA surfaces.…”

Chemical Mechanical Planarization-Related to Contaminants: Their Sources and Characteristics

“…The brush is compressed to the wafer surfaces, and then the particle contaminants are removed by the physical force of the compressed brush. However, the surface and inside the pore structure of PVA brushes are contaminated with the particles, organic residues, and pad debris (Figure 4a), which can be transported to the next wafers and cause cross-contamination of the wafers during the brush scrubbing [56,58]. More cross-contamination is observed on the wafer surfaces when the contact pressure and contact area between the brush and the wafer increase [59].…”

“…Before brush scrubbing, brush soaking treatment and break-in and their optimized process may be useful to reduce the cross-contamination and improve the cleaning efficiency [58]. Also, the ultrasonication method with DIW was very effective in removing the contaminants from the PVA brushes without damage [56].…”

“…(b) Wafer backside signature after CMP and cleaning process. Reproduced with permission from Ref [56]…”