Charged particle beam apparatus

A method using a charged particle beam apparatus which comprises

• a chamber configured to accommodate a sample with, an inside of the chamber being decompressed,
• a tube having an opening disposed in the chamber,
• a first beam generator, and
• a mixed gas generator,
• the method comprising:
• providing, by the mixed gas generator, a mixed gas having a plurality of types of gases to the tube;
• introducing, via the tube, the mixed gas in a direction towards the sample, substantially perpendicular to a direction of an elongated shape of an opening of the tube in a cross section;
• and
• emitting, by the first beam generator, a charged particle beam toward at least one of a region between the opening of the tube and the sample, or a region of the sample against which the mixed gas collides.