Several-ten nanometer-width Ge Fin structure with defect-free, vertical and smooth sidewall were successively delineated by a neutral beam etching method using pure Cl2 gas chemistry for developing three dimensional channel FETs. The cross-sectional profile of the Ge Fins tended to have bottom tails without undercuts beneath etching masks in the best etching conditions. The bottom tails were eliminated by increasing Cl neutral beam energy and increasing substrate temperature. Very precise dimension control became possible by adjusting those two conditions. High resolution TEM observations revealed that the Ge Fin sidewalls, which were supposed to be FET channels, etched by the neutral beam seemed very smooth in a substantially atomic level while those ones etched in a plasma had relatively rough surfaces due to plasma damages.