CMP PAD CLEAN FOR CERIA SLURRIES
Publication Date: 2009-May-08
The IP.com Prior Art Database
Disclosed herein are non-limiting embodiments of a composition and process for preventing the build-up of slurry residue and polishing by products on the pad during Chemical Mechanical Planarization (CMP) of dielectrics using ceria based slurries.
The build up is accelerated at conditions where the ceria particles and silicates have opposite charges, i.e. at pH 2 to 7 where ceria is below its isoelectric point (IEP), giving a positively charged surface, and silica is above its IEP, resulting in a negative charge.
A solution to this problem, according to some embodiments of the current invention, is to adjust the charge on one of the surfaces such that the species are all similarly charged and repel rather than attracting one another. This can be accomplished by using an ion that will specifically adsorb to silica and reverse the surface charge, causing silica to be positively charged at a pH that it would normally be negative in the absence of the added ions.
In some embodiments, a group of ions for this purpose include the tetraalkylammonium ions, of which tetramethyl ammonium is most preferred. Tetramethyl ammonium ions can be added as tetramethylammonium hydroxide. In some embodiments, an acid may also be added to adjust the pH to a value where the ceria surface is also positively charged (pH < 7). Preferred acids for pH adjustment are lactic, acetic, gluconic, glycolic, propionic, or phosphoric. Likewise in some embodiments, the build-up can be prevented by changing the surface charge on ceria to negative by specifically adsorbing an anion onto the surface. In some embodiments, suitable anions include citrate, malate, malonate, oxalate, succinate, tartra...