Almost Complete Removal of Ceria Particles Down to 10 nm Size from Silicon Dioxide Surfaces

Abstract

It has been very difficult to remove smaller ceria particles from silicon dioxide surfaces. One of the likely reasons is that the smaller ceria particles with a higher surface concentration of Ce 3+ are more strongly coupled with silicon dioxide surfaces via strong Ce-O-Si bonding. Here, we show that some equimolar solutions containing H 2 O 2 and either NH 4 OH or KOH, aided by ultrasonic cleaning, and at high pH can almost completely remove even 10 nm sized ceria particles from silicon dioxide film surfaces. The particles on the oxide surface before and after cleaning were imaged using atomic force microscopy and counted. The optimal composition of H 2 O 2 -NH 4 OH solutions was identified by investigating ten solutions with different compositions using an augmented simplex-centroid method along with four H 2 O 2 -KOH solutions. Equimolar mixtures of H 2 O 2 and NH 4 OH or KOH with the highest possible perhydroxyl ion concentration [HO 2 − ] showed ∼99% cleaning efficiency for 10 nm ceria particles. We propose that the strong Ce-O-Si bonding can be ruptured effectively by the nucleophile HO 2 − , formed by the decomposition of H 2 O 2 in the high pH environment, and show that [HO 2 − ] is highest in equimolar solutions. The cleaning efficiencies for 10 nm, 30 nm and 90 nm particles correlate very nicely with [HO 2 − ].

Investigation on the Material Removal and Surface Generation of a Single Crystal SiC Wafer by Ultrasonic Chemical Mechanical Polishing Combined with Ultrasonic Lapping

“…Compared with Figure 4 a, the new presence of Si-C-O bond and Si-O bond suggest that the oxide layer formed on the Si-face surface after ultrasonic chemical corroding. The presence mechanism of Si-O bound can refer to the following Equations (2)–(5) [ 26 , 27 ]. The analysis results indicate that ultrasonic can contribute to driving the chemical corroding during CMP, which is due to the temperature rise and bubble movement, because when bubbles collapse in liquid, it results in an enormous concentration of energy from the conversion of the kinetic energy of liquid motion into heating of the contents of the bubble.…”

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

“…Earlier, we demonstrated the ceria particles adsorbed on oxide surfaces via strong Ce-O-Si bond could not be removed effectively by only charge repulsion [5]. pH-adjusted DIW (pH 13.5) showed negligible cleaning efficiency (<5%) for 90 nm ceria particles, even when aided by ultrasonic cleaning [5]. In Figure 6: EW microscopy images of ceria particles adsorbed at (a) pH 3, (b) pH 5, (c) pH 7 and their removal using DIW adjusted to pH 10 and 12 as a function of number of washes.…”

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

“…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].…”

“…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]. It is well known that the surface Ce 3+ species are the active sites for the formation of strong Ce-O-Si bonds with SiO 2 films during polishing [4,21]. Various ceria abrasives such as smaller particles with higher surface Ce 3+ concentrations [35], the core/shell type Ce 3+ rich ceria [36], and metal-doping or coated ceria abrasive [37] have been investigated to improved SiO 2 removal rates, but making their removal during cleaning more difficult.…”

“…Some equimolar solutions containing NH 4 OH and H 2 O 2 (4.20 and 4.13 mol/L, respectively) to remove even 10 nm ceria particles (~99% cleaning efficiencies) from SiO 2 films were proposed by Seo et al [21]. Non-traditional cleaning solutions composed of a bond-breaking reagent, complexing reagent, cleaning additive and pH adjuster were proposed for post STI CMP cleaning process [62,63].…”