Charged particle beam apparatus permitting high-resolution and high-contrast observation
View Patent ↗A lower pole piece of an electromagnetic superposition type objective lens is divided into an upper magnetic path and a lower magnetic path. A voltage nearly equal to a retarding voltage is applied to the lower magnetic path. An objective lens capable of acquiring an image with a higher resolution and a higher contrast than a conventional image is provided. An electromagnetic superposition type objective lens includes a magnetic path that encloses a coil, a cylindrical or conical booster magnetic path that surrounds an electron beam, a control magnetic path that is interposed between the coil and sample, an accelerating electric field control unit that accelerates the electron beam using a booster power supply, a decelerating electric field control unit that decelerates the electron beam using a stage power supply, and a suppression unit that suppresses electric discharge of the sample using a control magnetic path power supply. Thus, whether landing energy of an electron beam varies widely, the electron beam can be focused with the electromagnetic superposition type objective lens approached to the sample.
1. A charged particle beam apparatus that irradiates a primary charged particle beam to a sample and detects secondary charged particles generated due to the irradiation, comprising:
an objective lens that focuses the primary charged particle beam on the sample; and
means for applying a retarding voltage to the sample,
wherein the objective lens includes:
an opening through which the charged particle beam passes;
a yoke member formed with a hollowed annular member which is disposed around a center axis of the objective lens passing through the opening;
a booster magnetic path member disposed in a space between the yoke member and the center axis of the objective lens; and
a control magnetic path member disposed in a space between the bottom of the yoke member and the sample; and
a magnetic flux concentration on a gap between the booster magnetic path member and the control magnetic path member, and
wherein the objective lens is configured to transfer the excited magnetic flux of the yoke member to the booster magnetic path member and the control magnetic path member, and
a potential at the control magnetic path member is controlled to be a potential that is equal to or higher than the retarding voltage and that is lower than the potential at the yoke member.
2. The charged particle beam apparatus according to claim 1 , wherein a potential difference between a potential at the sample and the potential at the control magnetic path member is controlled to fall within 100 V.
3. The charged particle beam apparatus according to claim 2 , wherein the potential at the control magnetic path member is controlled to be equal to the potential at the sample.
4. The charged particle beam apparatus according to claim 1 , wherein an accelerating voltage for use in accelerating the primary charged particle beam is applied to the booster magnetic path member.
5. The charged particle beam apparatus according to claim 1 , further comprising means for electrically isolating the yoke and control magnetic path members from each other.
6. The charged particle beam apparatus according to claim 1 , wherein the yoke member is brought to a ground potential.
7. The charged particle beam apparatus according to claim 1 , wherein a bottom of the yoke member has a conical shape with the opening, and the control magnetic path 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.
8. The charged particle beam apparatus according to claim 1 , further comprising an electrostatic adsorption device that holds the sample.
9. The charged particle beam apparatus according to claim 7 , wherein the electrostatic adsorption device includes an internal electrode that is opposed to the sample with a dielectric between them, and a contact electrode that applies the retarding voltage to the sample, further comprising:
means for retaining a potential difference between a potential at the contact electrode and the potential at the control magnetic path member at a value falling within ±100 V.
10. The charged particle beam apparatus according to claim 1 , further comprising a cooling member for the control magnetic path member.
11. The charged particle beam apparatus according to claim 1 , further comprising means for acquiring a shaded image of a position of irradiation of the primary charged particle beam.
12. The charged particle beam apparatus according to claim 1 , wherein the control magnetic path member has two magnetic plates of an upper magnetic plate and a lower magnetic plate; and
the lower magnetic plate is brought to a same potential as a potential at the sample.