Cleaning Solutions for Removal of ∼30 nm Ceria Particles from Proline and Citric Acid Containing Slurries Deposited on Silicon Dioxide and Silicon Nitride Surfaces

Abstract

A previously developed aqueous cleaning solution (4.2 mol l−1 each of H2O2 and NH4OH) was found to be ineffective in cleaning oxide/nitride surfaces after contamination with ceria particles from slurries containing proline or citric acid. However, a cleaning solution consisting of 1 wt% ascorbic acid, 1 wt% ammonium carbonate and 50 ppm triton X-100 at pH 12, aided by ultrasonic cleaning, removed these ceria particles, even those as small as ∼30 nm, from both oxide and nitride surfaces with efficiencies >99% as determined by AFM imaging. Fourier transform infrared (FTIR) spectroscopy results indicated that ceria particles treated with these additives can also bind with oxide/nitride surfaces through Si–O–C and Si–O–H bonds, in addition to any Ce–O–Si, where the C and H atoms are from the additives adsorbed on the ceria particles. All these bonds are broken effectively by the nucleophilic attack of hydroxyl anions in the cleaning solution while triton X-100 in the cleaning solution reduces adhesion between the particles and the film surface and facilitates cleaning via a wetting mechanism. More importantly, ascorbic acid and ammonium carbonate prevent particle redeposition by complexing with the removed particles and blocking the active Ce3+ species on their surface.

3D trajectories and diffusion of single ceria particles near a glass surface and their removal

“…Ceria particle-based slurries have been widely used for SiO 2 polishing, especially for shallow trench isolation (STI) chemical mechanical planarization (CMP) because of their high chemical affinity toward SiO 2 films [34]. However, this affinity presents a major challenge for post-CMP cleaning as the particles strongly adhere to the wafer surface during polishing [5,35]. With device dimensions, now at 7 nm, continuing to shrink, there is a strong need to understand various chemical and mechanical phenomena that occur in the brush cleaning systems used to remove these particles.…”

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

“…The surface charges of ceria abrasive are different depending on the nature of additives (e.g., dispersant, passivation agent for high selectivity, etc.) and the slurry pH [33]. Positively charged ceria particles, dispersed with amino acid, led significant contamination of negatively charged SiO 2 films while negatively charged ceria particles, dispersed with a weak organic acid or poly(acrylic acid), showed a higher level of contamination of Si 3 N 4 films [33].…”

“…Ceria-based slurry has been widely used for STI CMP to uniformly polish the step height of SiO 2 , formed by the gap-filling process, and stop on an underlying Si 3 N 4 film [4][5][6]. Residual ceria abrasives are discovered after STI CMP process (Figure 2c) [21,33]. In contrast with a silica abrasive, ceria abrasive is more strongly coupled with the dielectric materials (in particular, SiO 2 film) via the formation of strong Ce-O-Si bonding [4,34].…”

“…and the slurry pH [33]. Positively charged ceria particles, dispersed with amino acid, led significant contamination of negatively charged SiO 2 films while negatively charged ceria particles, dispersed with a weak organic acid or poly(acrylic acid), showed a higher level of contamination of Si 3 N 4 films [33]. Thus, cleaning of ceria particles from the wafer surfaces has become more challenging.…”

A review on chemical and mechanical phenomena at the wafer interface during chemical mechanical planarization

“…should be avoided during polishing. Since this is not always possible, post-CMP cleaning has become a crucial step to eliminate many of these defects [141,142,143,144]. Recently, the author not only showed that the rupture of a strong chemical bonding between abrasive particles and the SiO 2 films via a nucleophilic attack could help remove the particles from the surface [141] but also reported a stability constant-based strategy to study reagents that can remove Cu-BTA and Co-BTA complexes from various surfaces (Cu, Co, TaN, and SiO 2 films) [109,110].…”