Ion beam device and cleaning method for gas field ion source
An ion beam device according to the present invention suppresses the fluctuation of an ion emission current by cleaning the inside of a chamber without entailing wear damage to an emitter electrode. The ion beam device includes a GFIS including an emitter electrode having a needle-shaped tip; an extraction electrode having an opening at a position spaced apart from the tip of the emitter electrode; and a chamber encapsulating the emitter electrode therein. The GFIS includes an ionizable gas introduction path for introducing an ionizable gas into the chamber in a state where a voltage equal to or more than a beam generating voltage is applied to the emitter electrode; and a cleaning gas introduction path for introducing a cleaning gas into the chamber in either a state where a voltage less than the beam generating voltage is applied to the emitter electrode or a state where no voltage is applied to the emitter electrode. A pressure of the chamber with the cleaning gas introduced therein is higher than a pressure of the chamber when the ionizable gas is introduced therein.
1. An ion beam device comprising a gas field ion source which includes: an emitter electrode having a needle-shaped tip; an extraction electrode having an opening at a position spaced apart from the tip of the emitter electrode; and a chamber encapsulating the emitter electrode therein,
wherein the gas field ion source includes:
an ionizable gas introduction path for introducing an ionizable gas into the chamber in a state where a voltage equal to or more than a beam generating voltage is applied to the emitter electrode; and
a cleaning gas introduction path for introducing a cleaning gas into the chamber in either a state where a voltage less than the beam generating voltage is applied to the emitter electrode or a state where no voltage is applied to the emitter electrode, and
wherein a pressure of the chamber with the cleaning gas introduced therein is higher than a pressure of the chamber when the ionizable gas is introduced therein.
2. The ion beam device according to claim 1 ,
wherein when the cleaning gas is introduced into the chamber, the temperature of the emitter electrode is raised higher than when the ionizable gas is introduced.
3. The ion beam device according to claim 2 , further comprising a cooling device for cooling the emitter electrode,
wherein the cooling device is activated when the ionizable gas is introduced into the chamber, and
wherein the cooling device is deactivated when the cleaning gas is introduced into the chamber.
4. The ion beam device according to claim 1 ,
wherein electric discharge in the chamber is suppressed in a state where the cleaning gas is introduced in the chamber.
5. The ion beam device according to claim 1 ,
wherein the purity of the cleaning gas is lower than the purity of the ionizable gas.
6. The ion beam device according to claim 1 ,
wherein the ionizable gas introduction path is provided with a purification part for purifying the ionizable gas.
7. The ion beam device according to claim 6 ,
wherein the purification part is a film for selective permeation of the ionizable gas.
8. The ion beam device according to claim 1 ,
wherein the molecular weight of the cleaning gas is equal to or less than the molecular weight of the ionizable gas.
9. The ion beam device according to claim 1 ,
wherein the cleaning gas is a mixture gas containing a gas having a molecular weight equal to or less than a molecular weight of the ionizable gas.
10. The ion beam device according to claim 1 ,
wherein the cleaning gas contains hydrogen.
11. The ion beam device according to claim 1 ,
wherein the ionizable gas is hydrogen.
12. The ion beam device according to claim 1 ,
wherein two or more types of gases are used as the ionizable gas, and
wherein the cleaning gas contains a gas having a molecular weight lower than any of the molecular weights of the two or more types of gases.
13. The ion beam device according to claim 1 , further comprising a control unit which controls the introduction of the cleaning gas into the chamber in either a case where the length of operating time of the gas field ion source exceeds a predetermined value or a case where the stability of the ion beam emitted from the gas field ion source is decreased to less than a predetermined value.
14. A cleaning method for a gas field ion source which includes: an emitter electrode having a needle-shaped tip; an extraction electrode having an opening at a position spaced apart from the tip of the emitter electrode; and a chamber encapsulating the emitter electrode therein, and which generates an ion beam by introducing an ionizable gas into the chamber in a state where a voltage equal to or higher than a beam generating voltage is applied to the emitter electrode,
the method comprising a first step of increasing the pressure of the chamber to level higher than a pressure to introduce the ionizable gas, by introducing the cleaning gas into the chamber either in a state where a voltage less than the beam generating voltage is applied to the emitter electrode or a state where no voltage is applied to the emitter electrode.
15. The cleaning method for gas field ion source according to claim 14 , further comprising a second step of discharging the cleaning gas from the chamber,
wherein the first step and the second step are repeated or the first step and the second step are concurrently performed.
16. The cleaning method for gas field ion source according to claim 14 ,
wherein the first step is performed in either a case where the length of operating time of the gas field ion source exceeds a predetermined value or a case where the stability of the ion beam is decreased to less than a predetermined value.