Patent Number: 
Section: claims

1. A charged particle beam apparatus, comprising:a stage for placing a sample thereon;a detector detecting secondary charged particles generated due to irradiate a primary charged particle beam to the sample;an objective lens that focuses the primary charged particle beam on the sample and having an opening through which the primary charged particle beam passes; anda power supply unit applying a negative voltage to the sample,wherein the objective lens includes:a first magnetic pole member that is disposed around the opening and has a terminal portion at a sample side thereof that functions as an upper magnetic pole member of the objective lens;a second magnetic pole member that supplies a magnetic flux to the first magnetic pole member and is formed with a hollow interior;a coil that is disposed within the second magnetic pole member and supplies a magnetic flux to the second magnetic pole member; anda third magnetic pole member that is disposed between the stage and the second magnetic pole member, has the opening and functions as lower magnetic pole member of the objective lens, andwherein a potential lower than that of the second magnetic pole member is supplied to the third magnetic pole member. 2. The charged particle beam apparatus according to claim 1, further comprising:means for supplying a retarding potential to the sample,wherein a potential higher than the retarding potential is supplied to the third magnetic pole member. 3. The charged particle beam apparatus according to claim 2,wherein a potential difference between a potential at the sample and a potential at the third magnetic pole member is within 100V. 4. The charged particle beam apparatus according to claim 3,wherein the potential at the third magnetic pole member is equal to the potential at the sample. 5. The charged particle beam apparatus according to claim 2,wherein an accelerating potential for accelerating the primary charged particle beam is applied to the first magnetic pole member. 6. The charged particle beam apparatus according to claim 1, further comprising:means for electrically isolating the second magnetic pole member and the third magnetic pole member from oath other. 7. The charged particle beam apparatus according to claim 1, wherein the second magnetic pole member is brought to a ground potential. 8. The charged particle beam apparatus according to claim 1,wherein a bottom of the second magnetic pole member has a conical shape with the opening, and wherein the third magnetic pole member is realized with a magnetic plate disposed in parallel with a conical surface of the conically-shaped bottom with a predetermined gap left from the conical surface. 9. The charged particle beam apparatus according to claim 1, further comprising:an electrostatic adsorption device that holds the sample. 10. The charged particle beam apparatus according to claim 9,wherein the electrostatic adsorption device includes:an internal electrode that is opposed to the sample with a dielectric between them;a contact electrode that applied a retarding voltage to the sample; andmeans for retaining a potential difference between a potential at the contact electrode and a potential at the third magnetic pole member at a value falling within −±100V. 11. The charged particle beam apparatus according to claim 1, further comprising:a cooling member for the third magnetic pole member. 12. The charged particle beam apparatus according to claim 1, further comprising:means for acquiring a shaded image of a portion of irradiation of the primary charged particle beam. 13. The charged particle beam apparatus according to claim 1,wherein the third magnetic pole member has two magnetic plates of an upper magnetic plate and a lower magnetic plate; andwherein the lower magnetic plate is brought to a same potential as a potential at the sample.