Energy filter for charged particle beam apparatus
This invention provides two methods for improving performance of an energy-discrimination detection device with an energy filter of reflective type for a charged particle beam. The first method employs a beam-adjusting means to improve the energy-discrimination power, and the second method uses an electron-multiplication means to enhance the image signal without noise raise. A LVSEM with such an improved energy-discrimination detection device can provide variant high-contrast images of interested features on a specimen surface for multiple application purposes.
1. An energy-discrimination detection device for detecting an electron beam, comprising:
an energy filter, comprising:
a filtering grid electrode being set at a first potential to form a potential barrier; and,
a beam-adjusting lens below said filtering grid electrode and being excited to make said electron beam become a substantially parallel beam to be incident onto said potential barrier,
wherein a first plurality of electrons of said electron beam, which has initial kinetic energies higher than a specific value and thus is able to cross said potential barrier, passes through said filtering grid electrode and forms an exiting electron beam, while a second plurality of electrons of said electron beam, which has initial kinetic energies not higher enough to be able to cross said potential barrier, is reflected back from said filtering grid electrode and forms a reflection electron beam;
an electron-multiplication plate above said energy filter and comprising an electron-multiplication surface, wherein said electron-multiplication surface is made of electric conductor material which can generate a secondary emission with a total yield (σ) higher than 1; and
a first detector above said energy filter and beside said electron-multiplication plate,
wherein said electron-multiplication surface is placed and set at a second potential to attract said first plurality of electrons to land thereon and generate said secondary emission,
wherein said first detector is placed and set at a third potential to receive electrons of a secondary emission beam of said secondary emission,
wherein an optical axis of said beam-limiting lens is both an optical axis of said energy filter and an optical axis of said energy-discrimination detection device.
2. The energy-discrimination detection device according to claim 1 , wherein said filtering grid electrode is perpendicular to and aligned with said optical axis of said beam-adjusting lens.
3. The energy-discrimination detection device according to claim 2 , further comprising a shielding box covering said energy filter, said electron-multiplication plate and said first detector, wherein said shielding box is made of electric conductor material and has an entrance plate which is below said energy filter, perpendicular to said optical axis and has an entrance grid for said electron beam passing through.
4. The energy-discrimination detection device according to claim 3 , wherein said shielding box is set at a potential of a neighborhood where said energy-discrimination detection device is placed.
5. The energy-discrimination detection device according to claim 4 , further comprising a second detector below said entrance grid, wherein said second detector has an opening for a central part of said electron beam passing through and fully or partially detects other part thereof.
6. The energy-discrimination detection device according to claim 4 , further comprising a third detector being placed and excited to detect said reflection electron beam.
7. The energy-discrimination detection device according to claim 1 , wherein said second potential is adjusted to maximize said total yield so as to enhance an image signal of said first detector.
8. The energy-discrimination detection device according to claim 1 , further comprising a shielding grid electrode placed in front of said first detector and set at a fourth potential, wherein said fourth potential is lower enough than said third potential so that said shielding grid electrode is not able to directly attract said first plurality of electrons, but higher enough than said second potential so as to attract electrons of said secondary emission beam.
9. An energy-discrimination detection device for detecting an electron beam, comprising:
an energy filter, comprising:
a filtering grid electrode being set at a first potential to form a potential barrier; and,
a beam-adjusting lens below said filtering grid electrode and being excited to make said electron beam become a substantially parallel beam to be incident onto said potential barrier,
wherein a first plurality of electrons of said electron beam, which has initial kinetic energies higher than a specific value and thus is able to cross said potential barrier, passes through said filtering grid electrode and forms an exiting electron beam, while a second plurality of electrons of said electron beam, which has initial kinetic energies not higher enough to be able to cross said potential barrier, is reflected back from said filtering grid electrode and forms a reflection electron beam;
a microchannel plate (MCP) above said energy filter; and
a first detector above said microchannel plate,
wherein an input surface and channel axes of said microchannel plate are set to receive said first plurality of electrons and generate sequential secondary emissions inside a channel thereof,
wherein said first detector is set to receive electrons of a secondary emission beam exiting from an outer surface of said microchannel plate,
wherein an optical axis of said beam-limiting lens is both an optical axis of said energy filter and an optical axis of said energy-discrimination detection device.
10. The energy-discrimination detection device according to claim 9 , wherein said filtering grid electrode is perpendicular to and aligned with said optical axis of said beam-adjusting lens.
11. The energy-discrimination detection device according to claim 10 , further comprising a shielding box covering said energy filter, said microchannel plate and said first detector, wherein said shielding box is made of electric conductor material and has an entrance plate which is below said energy filter, perpendicular to said optical axis and has an entrance grid for said electron beam passing through.
12. The energy-discrimination detection device according to claim 11 , wherein said shielding box is set at a potential of a neighborhood where said energy-discrimination detection device is placed.
13. The energy-discrimination detection device according to claim 12 , further comprising a second detector below said entrance grid, wherein said second detector has an opening for a central part of said electron beam passing through and fully or partially detects other part thereof.
14. The energy-discrimination detection device according to claim 12 , further comprising a third detector being placed and excited to detect said reflection electron beam.
15. An electron beam apparatus for observing a surface of a specimen, comprising:
an electron source being excited to emit primary electrons along an optical axis of said electron beam apparatus;
an accelerating electrode below said electron source and having an opening aligned with said optical axis for said primary electrons passing through, which is excited to accelerate said primary electrons to have desired first energies;
a condenser lens below said accelerating electrode and aligned with said optical axis;
a beam-limiting aperture plate below said condenser lens and having a plurality of apertures with different radial sizes, wherein one of said plurality of apertures is selected as a beam-limit aperture and thus aligned with said optical axis,
wherein said condenser lens is excited to make a part of said primary electrons pass through said beam-limit aperture so as to form a primary electron beam with a desired current value;
a magnetic objective lens below said beam-limiting aperture plate and aligned with said optical axis;
a retarding electrode below said magnetic objective lens and having an opening aligned with said optical axis for said primary electron beam passing through;
a specimen stage below said retarding electrode and supporting said specimen, wherein said surface is opposite to said retarding electrode;
a deflection unit between said beam-limiting aperture plate and said retarding electrode,
wherein said retarding electrode and said specimen are excited to decelerate said primary electrons of said primary electron beam to land on said surface with desired second energies much lower than said first energies,
wherein said magnetic objective lens is excited to focus said primary electron beam to form a focused probe on said surface and said focused probe releases a first secondary emission beam therefrom,
wherein said deflection unit deflects said primary electron beam and thus makes said focused probe scan said surface;
an energy-discrimination detection device above said deflection unit and away from said optical axis, which comprises an energy filter, an electron-multiplication means and a first detector,
wherein said energy filter comprises a filtering grid electrode and a beam-adjusting lens, said filtering grid electrode functions as a potential barrier, said beam-adjusting lens is below said filtering grid electrode and functions as a means for adjusting an incident electron beam of said energy filter to become a substantially parallel beam to be incident onto said potential barrier, and consequently a first plurality of electrons of said incident electron beam, which has initial kinetic energies higher than a specific value and thus is able to cross said potential barrier, passes through said filtering grid electrode and forms an exiting electron beam, while a second plurality of electrons of said incident electron beam, which has initial kinetic energies not higher enough to be able to cross said potential barrier, is reflected back from said filtering grid electrode and forms a reflection electron beam,
wherein said electron-multiplication means is above said energy-filter and set to receive said exiting electron beam which generates a second secondary emission therein, and output a second secondary emission beam with a total yield (σ) higher than 1,
wherein said first detector is above said energy-filter and set to detect said second secondary emission beam; and
a Wien filter between said specimen and said energy-discrimination detection device.
16. The electron beam apparatus according to claim 15 , wherein said Wien filter is excited to deflect said first secondary emission beam to be incident onto said energy-discrimination detection device while not deflecting said primary electron beam, and therefore said first secondary emission beam is said incident electron beam of said energy filter.
17. The electron beam apparatus according to claim 15 , further comprising a second detector above said deflection unit and away from said optical axis, wherein said Wien filter is excited to deflect said first secondary emission beam to be detected by said second detector while not deflecting said primary electron beam.
18. The electron beam apparatus according to claim 15 , wherein said electron-multiplication means is an electron-multiplication plate with an electron-multiplication surface aligned to receive said exiting electron beam and generate said second secondary emission beam.
19. The electron beam apparatus according to claim 18 , further comprising a shielding grid electrode placed in front of said first detector and functioning as a means for making more of said first plurality of electrons hitting said electron-multiplication surface and attracting more of electrons of said second secondary emission beam towards said first detector.
20. The electron beam apparatus according to claim 15 , wherein said electron-multiplication means is a microchannel plate, an input surface and channel axes of said microchannel plate are set to receive said exiting electron beam, generate a series of said second secondary emissions in a channel thereof and output said second secondary emission beam from an outer surface of said microchannel plate.