Cleaning Solutions for Removal of ∼30 nm Ceria Particles from Proline and Citric Acid Containing Slurries Deposited on Silicon Dioxide and Silicon Nitride Surfaces
Akshay Gowda, Jihoon Seo, C. K. Ranaweera, S. V. Babu
Abstract
A previously developed aqueous cleaning solution (4.2 mol l −1 each of H 2 O 2 and NH 4 OH) 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 Ce 3+ species on their surface.