Investigation into the Effect of CMP Slurry Chemicals on Ceria Abrasive Oxidation State using XPS

Abstract

The ratio of Ce3+/Ce4+ on the surface of ceria CMP slurry abrasives was maximized by altering the slurries’ chemical environment. Maximizing this ratio increases the proportion of active Ce3+ sites which participate in removal reactions, leading to increased removal rates. Small amounts of peroxide and surfactant were added to three ceria slurries at varying pH values to determine how these chemicals affected the different particle surfaces. The effects of these chemicals on the oxidation ratio were determined through XPS analysis of the Ce 3d spectrum. The addition of surfactants to ceria slurry, while necessary to increase particle dispersibility, decreased the Ce3+/Ce4+ ratio and therefore limited chemical removal. Of the conditions tested, pH had no effect, surfactants decreased the ratio, and peroxide could either increase or decrease the ratio based on concentration. Understanding these interactions will help to inform the design of future ceria CMP slurries to maximize their effectiveness.

Fused silica with sub‐angstrom roughness and minimal surface defects polished by ultrafine nano‐CeO2

“…As shown in Figure 7A, the contact angle of polished fused silica decreases with the increase of Ce 3+ concentration. The oxidability of Ce 3+ makes it easier to react with oxygen atoms that on the fused silica surface to break Si–O bond, 20,26,52 then more silanol groups (Si–OH) will be generated with the participation of water molecules, 53 in Figure 7B. The surfaces of Si–OH whose Si–O bond that connects to the fused silica matrix has been broken are more easily removed by mechanical action of CeO 2 .…”

“…51 As shown in Figure 7A, the contact angle of polished fused silica decreases with the increase of Ce 3+ concentration. The oxidability of Ce 3+ makes it easier to react with oxygen atoms that on the fused silica surface to break Si-O bond, 20,26,52 then more silanol groups (Si-OH) will be generated with the participation of water molecules, 53…”

“…Many studies in recent years have achieved a certain reduction in surface roughness by changing the size, 22 morphology, 23 structure, 24 and chemical properties 25 of CeO 2 , and there is still a long way to go for industrial manufacture requiring low cost and high efficiency. Ce elements with a valence of +3 (Ce 3+ ) that in CeO 2 have considered to be one of the most vital factors affecting the MRR in CMP under the premise of similar particle size, 25,26 which increases MRR by augmenting the reactive sites on fused silica surface, 20 so the accurate characterization of Ce 3+ concentration is beneficial to the optimization of polishing process. X‐ray photoelectron spectroscopy (XPS) is the most commonly used method for analyzing the valence of Ce element in CeO 2 22,25,27 .…”

Coupling Supramolecular Assemblies and Reactive Oxygen Species (ROS) with Megasonic Action for Applications in Shallow Trench Isolation (STI) Post-Chemical Mechanical Planarization (p-CMP) Cleaning

“… 10 , 11 It has been widely accepted that the particle left on the TEOS wafer post-polish is predominantly Ce 3+ as the presence of surface oxygen vacancies is critical during the polishing step. 4 , 12 − 16 This strong noncovalent interaction between the CeO 2 nanoparticle and wafer surface means that the cleaning chemistries used in the p-CMP process require a redox-active cleaning environment so that the particle can be removed via the charge flipping mechanism (i.e., converting Ce 3+ to Ce 4+ ). While this has shown to be an effective mode of particle removal, there is an increase in the process shear force (mechanical component), which results in secondary defect formation (i.e., increased scratching/surface roughness).…”

“…With device feature size and complexity continuing to approach the 3 nm node, limiting induced defectivity during not only the polishing process but also the post-chemical mechanical planarization (p-CMP) process is of utmost importance. − To effectively achieve this, an understanding of the interactions between the slurry residue and cleaning formulations at the molecular level is crucial. Traditional p-CMP processes for STI involve a contact method of cleaning through PVA brush scrubbing. − This contact method has been coupled with different cleaning chemistry types, such as redox additives and surfactants, to effectively remove residual CeO 2 nanoparticles on the surface. , It has been widely accepted that the particle left on the TEOS wafer post-polish is predominantly Ce 3+ as the presence of surface oxygen vacancies is critical during the polishing step. ,− This strong noncovalent interaction between the CeO 2 nanoparticle and wafer surface means that the cleaning chemistries used in the p-CMP process require a redox-active cleaning environment so that the particle can be removed via the charge flipping mechanism (i.e., converting Ce 3+ to Ce 4+ ). While this has shown to be an effective mode of particle removal, there is an increase in the process shear force (mechanical component), which results in secondary defect formation (i.e., increased scratching/surface roughness). , More recently attention has shifted to developing p-CMP cleaning formulations that employ encapsulation of the CeO 2 nanoparticle using supramolecular chemistries (i.e., surfactants, polyelectrolytes, liposomes, etc.).…”