Field-emission electron gun and method for controlling same
View Patent ↗The disclosed charged particle beam apparatus includes a field-emission electron source including <310> single crystal of tungsten; a vacuum chamber having the electron source therein; an exhausting system for exhausting the vacuum chamber; a filament connected to the electron source to let flow a current through the electron source and thereby heat the electron source; a power supply for letting a current flow through the filament; an ammeter for measuring a total current emitted from the electron source; and a controlling unit for exercising control to cause the power supply to let a current flow through the filament when the total current measured periodically has become a predetermined ratio or less as compared with a total current from the electron source found immediately after first electron beam emission, or a total current from the electron beam found immediately after a current is let flow through the filament.
1. A charged particle beam apparatus comprising:
a field-emission electron source comprising <310> single crystal of tungsten;
a vacuum chamber having the electron source disposed therein;
an exhausting system for exhausting the vacuum chamber;
a filament connected to the electron source to let flow a current through the electron source and thereby heat the electron source;
a power supply for letting a current flow through the filament;
an ammeter for measuring a total current emitted from the electron source; and
a controlling unit for exercising control to cause the power supply to let a current flow through the filament when the total current measured periodically has become a predetermined ratio of 30% - 70% or less as compared with a total current from the electron source found immediately after first electron beam emission, or a total current from the electron beam found immediately after a current is let flow through the filament.
2. The charged particle beam apparatus according to claim 1 , wherein the controlling unit exercises control to cause the power supply to let flow a current through the filament when the total current has become half as compared with a total current obtained immediately after electron beam emission or a total current obtained immediately after a current is let flow through the filament.
3. The charged particle beam apparatus according to claim 1 , comprising an operating unit for inputting time to let flow a current through the filament, a time period to let flow a current, and a current to the controlling unit.
4. The charged particle beam apparatus according to claim 1 , wherein the exhausting system keeps a pressure in the vacuum chamber at a 10 −9 Pa level or less.
5. The charged particle beam apparatus according to claim 4 , wherein parts in the vacuum chamber and the vacuum chamber are fabricated by using materials which can be heated to at least 300° C., and are subject to processing of degassing at a temperature of at least 300° C. in a vacuum furnace which maintains a pressure of a 10 −3 Pa level or less, for at least one hour.
6. The charged particle beam apparatus according to claim 4 , wherein a non-evaporable getter pump and an ion pump having an exhausting speed of at least 1 l/s are used jointly as the exhausting system.
7. The charged particle beam apparatus according to claim 4 , wherein a titanium sublimation pump and an ion pump are used jointly as the exhausting system.
8. The charged particle beam apparatus according to claim 4 , wherein a cryo pump is used as the exhausting system.
9. The charged particle beam apparatus according to claim 4 , wherein the exhausting system comprises:
a first stage turbomolecular pump having an exhausting speed of at least 100 l/s;
a second stage turbomolecular pump disposed at an exhausting port of the first stage turbomolecular pump; and
an auxiliary pump disposed at an exhausting port of the second stage turbomolecular pump.
10. The charged particle beam apparatus according to claim 1 , wherein a current is let flow through the filament once or a plurality of times for a determinate time period, and the electron source is raised in temperature to at least 1500K by heating resulting from current flowing.
11. The charged particle beam apparatus according to claim 1 , wherein the controlling unit suspends the control for letting flow a current through the filament, while a signal emitted from a sample is being detected.
12. The charged particle beam apparatus according to claim 1 , wherein the controlling unit suspends the control for letting flow a current through the filament, while the charged particle beam apparatus is being operated.
13. The charged particle beam apparatus according to claim 1 , wherein
the charged particle beam apparatus comprises a monitor, and
the controlling unit displays a message on the monitor to urge to let a current flow through the filament when the total current has become a predetermined ratio or less as compared with a total current from the electron source found immediately after electron beam emission or a total current from the electron beam found immediately after a current is let flow through the filament.
14. The charged particle beam apparatus according to claim 1 , wherein
an extraction electrode which ejects the electron beam from the electrode source is made of a thin metal wire,
a Faraday cup is provided on a ground side struck by said electron beam, and
an ammeter is disposed between the Faraday cup and the ground.