Patent Number: 
Section: abstract

A liquid metal ion gun 3 includes a liquid metal ion source 31 and a beam limiting aperture 33. The liquid metal ion source 31 includes a reservoir 36 and an emitter 35. The reservoir 36 is made of tungsten (W) and holds liquid metal gallium (Ga). The emitter 35 is made of W. The beam limiting aperture 33 is formed with a liquid metal member 44 made of Ga placed on a base 46 made of W, has an opening 41 that enables an ion beam 2 extracted from the liquid metal ion source 31 to pass therethrough, and limits the diameter of the ion beam 2. The beam limiting aperture 33 has a groove structure 45 that causes the liquid metal 44 to gather into a region located around the opening 41. The lifetime of the beam limiting aperture can be increased, and an emission can be maintained stable for a long time period and reproducibly restored to a stable state.