Communication—An Analysis of Shear Forces in Post-CMP PVA Brush Scrubbing for Stationary and Rotating Wafers

Abstract

After defining certain sign conventions for sliding velocity and shear force for a PVA brush scrubbing process, a simple kinematics model is used to calculate net sliding velocities in the brush-wafer contact region. Next, a series of experiments are performed where brush velocity is gradually increased while the wafer is kept stationery, and repeated again with the wafer rotating at a certain velocity. For a stationary wafer, with increasing brush velocity, partial lubrication takes effect which results in less brush asperity contact (i.e. a reduction in SF). For a rotating wafer, SF decreases significantly. We attribute this to the net negative sliding velocity across the wafer that partially offsets the positive SF values. However, SF rises with brush velocity which is likely due to fluid distribution effects and increased brush asperity-wafer contact.

Understanding the Reasons Behind Defect Levels in Post-Copper-CMP Cleaning Processes with Different Chemistries and PVA Brushes

“…8 and 9 show that mean SF increases proportionatelyy with Ω b . These results are consistent with a recent publication by Sampurno et al 30 that attributes the upward trend of SF with increasing brush asperity-wafer contact at higher Ω b . On the other hand, Figs.…”

“…Due to the complex kinematics of the system in which the axis of rotation of the wafer is always perpendicular to that of the brush, the magnitude of the local sliding velocity is governed not only by brush dimension and its rotational velocity but also by the velocity of the wafer. 30 As such, in certain regions, the local velocity vector is opposite to that of the brush, and in other regions, it is in the same direction. It is important to note the large ranges of local sliding velocities calculated, and how the point of net-zero velocity shifts to the right as brush velocity is increased.…”

“…SF extraction methods and the kinematics of the scrubber have been described in great detail elsewhere. 30…”

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

“…Traditional p-CMP processes for STI involve a contact method of cleaning through PVA brush scrubbing. 7 − 9 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. 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.…”

“…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.).…”