The energy and the flux of the ion gun with a three-grid system was compared with those of the ion gun with a two-grid system and the characteristics of the neutral beam sources composed of the ion guns with different grid systems and a reflector for the low angle reflection of the ions were investigated. By using the three-grid system instead of the two-grid system and by applying higher negative voltage to the 2nd grid, a higher ion flux without changing the ion energy could be obtained for the ion gun of the neutral beam source. The three-grid ion gun system generated higher neutral beam fluxes compared to the two-grid ion gun system. This result was confirmed by measuring the etch rates of Si and GaAs with Ar and fluorine neutral beam. Also, using the neutral beam source with the three-grid ion gun, 35nm-width Si patterns could be etched vertically by CF4 gas indicating the formation of a parallel neutral beam.