Dry Cleaning Technology for Removal of Silicon Native Oxide Employing Hot NH3/NF3Exposure

A new dry cleaning technology for removal of silicon (Si) native oxides from contact holes employing a hot ammonium (NH 3 )/nitrogen trifluoride (NF 3 ) mixture has been studied. The NH 3 /NF 3 mixture heated at a high temperature in a quartz tube enabled etching of the silicon dioxide (SiO 2 ) film placed in the downstream region. The mechanism of the etching reaction which was investigated using in-situ infrared spectroscopy and X-ray photoelectron spectroscopy analysis was revealed as follows: NF 3 alone in the NH 3 /NF 3 mixture was decomposed above 600°C, probably producing NF x ( x =1, 2) and fluorine atoms. These active species reacted with NH 3 , thereby generating ammonium hydrogen fluoride (NH 4 F ·HF) and/or ammonium fluoride (NH 4 F) in the gas phase which are considered to be SiO 2 etchants. The reaction of these molecules with SiO 2 generated an ammonium hexafluorosilicate ((NH 4 ) 2 SiF 6 ) product on the Si surface which was liberated at a temperature above 70°C, leaving the hydrogen terminated surface. The application of this method to actual contact holes demonstrated successful removal of the Si native oxide grown on the Si surface at the hole bottom.