A method is presented for forming a semiconductor device. The method includes depositing a sacrificial layer on a fin structure formed on a substrate and then filled with polysilicon, etching a portion of the polysilicon material via a first etching process, and pre-cleaning the surface native oxide layer. The method further includes etching the remaining polysilicon material via a second etching process, and removing polysilicon etch residue formed adjacent the fin structure by a cleaning process. The pre-cleaning is performed by applying NH3 (ammonia) and NF3 (nitrogen trifluoride) or by applying BHF (buffered hydrofluoric acid). The first etching process is RIE (reactive ion etching) and the second etching process involves applying NF3 and H2 (hydrogen gas).