Charged particle beam apparatus, and method of controlling the same
Provided is a charged particle beam apparatus, which can emit a stable electron beam, having high brightness and a narrow energy width. The charged particle beam apparatus comprises a field emission electron source, electrodes for applying an electric field to the field emission electron source, and a vacuum exhaust unit for keeping the pressure around the field emission electron source at 1 10−8 Pa or less. The apparatus is so constituted as to use such one of the electron beams emitted as has an electron-beam-center radiation angle of 1×10 −2 sr or less, and to use the electric current thereof, the second order differentiation of which is negative or zero with respect to the time, and which reduces at a rate of 10% or less per hour. The charged particle beam apparatus further comprises a heating unit for the field emission electron source, and a detection unit for the electric current of the electron beam. The field emission electron source is repeatedly heated to keep the electric current of the electron beam to be emitted, at a predetermined value or higher.
1. A charged particle beam apparatus including a field emission electron source and an electrode to apply an electric field to the field emission electron source, the apparatus comprising:
a vacuum exhaust unit for maintaining a pressure around the field emission electron source to be less than 1×10 −8 Pa,
wherein an electron beam having a central radiation angle within 1×10 −2 sr among electron beams emitted from the field emission electron source is used, and a second order differentiation about a time of current of the electron beam is minus or 0 for at least one hour after flashing of the field emission electron source.
2. The charged particle beam apparatus according to claim 1 , comprising:
a non-evaporative getter pump in the vacuum exhaust unit.
3. The charged particle beam apparatus according to claim 1 , comprising:
a heating unit of the field emission electron source, and a detector of current of the electron beam,
wherein the field emission electron source is repeatedly heated using the heating unit, and the current of the electron beam emitted from the field emission electron source is maintained greater than a predetermined value using an output of the detector.
4. The charged particle beam apparatus according to claim 3 , comprising:
a controller for controlling the heating unit,
wherein the controller controls the heating unit to heat the field emission electron source when the current of the electron beam reaches αI (o) with respect to an initial value I (o) of current I (t) of the electron beam emitted from the field emission electron source, and α≧0.8.
5. The charged particle beam apparatus according to claim 3 , comprising:
a controller for controlling the heating unit,
wherein the controller controls the heating unit to heat the field emission electron source when a decreasing ratio [I (t) −I (t+tc) ]/I (t) of current per time interval t c is greater than a predetermined value β with respect to the current I (t) of the electron beam emitted from the field emission electron source, and t c ≦60 minutes and β≧0.01.
6. The charged particle beam apparatus according to claim 3 , wherein a heating temperature of the field emission electron source is less than 2000 degrees.
7. The charged particle beam apparatus according to claim 3 , wherein in heating of the field emission electron source, the electron beam is normally emitted from the field emission electron source.
8. The charged particle beam apparatus according to claim 3 , comprising:
a manipulator for selecting whether to automatically performing heating of the field emission electron source using the controller; and
a display for displaying a result selected by the manipulator.
9. The charged particle beam apparatus according to claim 1 , comprising:
a heating unit of the field emission electron source,
wherein the electron beams emits from the field emission electron source while normally keeping heating the field emission electron source in 1500 degrees or less.
10. A control method of a charged particle beam apparatus including a field emission electron source and an electrode to apply an electric field to the field emission electron source, the method comprising:
maintaining a pressure around the field emission electron source to be less than 1×10 −8 Pa by a vacuum exhaust unit,
using an electron beam having a central radiation angle within 1×10 −2 sr among electron beams emitted from the field emission electron source, and
controlling a second order differentiation about a time of current of the electron beam to be minus or 0 for at least one hour after flashing of the field emission electron source.
11. The control method of a charged particle beam apparatus according to claim 10 , wherein the field emission electron source is repeatedly heated by a heating unit, and the current of the electron beam emitted from the field emission electron source is maintained to be greater than a predetermined value.