Patent Number: 
Section: claims

1. A charged-particle beam apparatus comprising:a chamber having an interior evacuated by an intra-chamber evacuating means; anda lens-barrel emitting a charged-particle beam onto a sample placed in the chamber,wherein the lens-barrel comprises:a cylindrical body having a distal end at which an emission outlet is formed for communication with the chamber and from which the charged-particle beam is released;a charged-particle supplier housed at a side of a proximal end in an interior of the cylindrical body to release the charged-particle beam; andan objective lens housed at a side of a distal end in the interior of the cylindrical body and having an electrostatic lens generating an electric field by voltage application and converging the charged-particle beam released from the charged-particle supplier, anda gas supplying means in the cylindrical body of the lens-barrel for supplying an inert gas into the cylindrical body at a side of a proximal end of the objective lens and configured to provide an inert gas pressure in the chamber sufficient to substantially prevent dust present in the chamber from contact with the objective lens. 2. The charged-particle beam apparatus according to claim 1, wherein the gas supplying means includes:a gas supply pipe having a distal end provided at the proximal end side of the objective lens;a gas supplier connected to a proximal end of the gas supply pipe to supply the gas; anda gas supply valve controlling an open/close state of the gas supply pipe. 3. The charged-particle beam apparatus according to claim 2, wherein the gas supply pipe of the gas supplying means is provided with a filter removing dust mixed in the gas supplied from the gas supplier. 4. The charged-particle beam apparatus according to claim 2, wherein in the gas supply pipe of the gas supplying means, at least the distal end arranged inside the cylindrical body comprises a metal. 5. The charged-particle beam apparatus according to claim 2, wherein in the gas supply pipe of the gas supplying means, at least the distal end arranged inside the cylindrical body is subjected to vacuum baking. 6. The charged-particle beam apparatus according to claim 1, further comprising:a cylindrical body valve interposed between the gas supplying means and the charged-particle supply part to control an open/close state of each of the distal end side and the proximal end side in the cylindrical body; anda supply part evacuating means provided at the proximal end side of the cylindrical body to maintain the proximal end side of the cylindrical body, in which the charged-particle supply part is housed, at an ultra high vacuum state which is higher than a vacuum state of the chamber. 7. The charged-particle beam apparatus according to claim 1, wherein the objective lens further has a magnetic field lens generating a magnetic field so as to superimpose the magnetic field on the electric field generated by the electrostatic lens and converging the charged-particle beam. 8. The charged-particle beam apparatus according to claim 1, wherein the gas supplying means is configured to supply the inert gas at a distal end of the cylindrical body. 9. The charged-particle beam apparatus according to claim 8, wherein the gas supplying means is configured to supply the inert gas such that an atmospheric pressure is created inside the chamber and the distal end of the cylindrical body.