Scanning electron microscope and apparatus for detecting defect
View Patent ↗A scanning electron microscope, by which an image of unevennesses on the surface of a sample may be obtained in a high-resolution manner and a high contrast one, is provided according to the present invention. A sample image is obtained by use of the scanning electron microscope with a configuration in which a positive voltage is applied in order to accelerate a primary electron beam, and an electric field shielding plate, a magnetic field shielding plate, or an electromagnetic field shielding plate is arranged on the upper side of an object lens.
1. A scanning electron microscope, having:
an electron source which generates a primary electron beam;
an object lens by which said primary electron beam is focused onto a sample;
a conductor plate, with which signal electrons which have a high energy of 10 electron volts or more and have been generated from said sample, collide;
two detectors which detect secondary electrons, which have been generated from said conductor plate;
an acceleration-electric-field generating unit which generates an acceleration electric field between said object lens and said conductor plate, wherein said signal electrons are accelerated by said acceleration electric field; and
a shielding plate arranged on the upper side of said object lens.
2. The scanning electron microscope according to claim 1 , wherein
said object lens is of a separate type, and consists of a separate pole in the center side region and a main pole in the outside region, and
said acceleration-electric-field generating unit is formed by said separate pole.
3. The scanning electron microscope according to claim 2 , wherein
said shielding plate is an electric field shielding plate by which said acceleration electric field is controlled.
4. The scanning electron microscope according to claim 2 , wherein
said shielding plate is a magnetic field shielding plate by which a magnetic field caused by a magnetic gap generated by the space between said two magnetic poles is controlled.
5. The scanning electron microscope according to claim 2 , wherein
said shielding plate is an electromagnetic field shielding plate by which a magnetic field caused by a magnetic gap generated by the space between said two magnetic poles is controlled, and said acceleration electric field is controlled.
6. The scanning electron microscope according to claim 1 , wherein
said acceleration-electric-field generating unit is formed by a ring-like electrode provided in the inner side of said object lens.
7. The scanning electron microscope according to claim 6 , wherein
said shielding plate is an electric field shielding plate by which said acceleration electric field is controlled.
8. The scanning electron microscope according to claim 6 , wherein
said shielding plate is a magnetic field shielding plate by which a magnetic field caused by a magnetic gap generated by the space between said two magnetic poles is controlled.
9. The scanning electron microscope according to claim 6 , wherein
said shielding plate is an electromagnetic field shielding plate by which a magnetic field caused by a magnetic gap generated by the space between said two magnetic poles is controlled, and said acceleration electric field is controlled.
10. The scanning electron microscope according to claim 1 , wherein
said object lens generates a leakage magnetic field by which said signal electrons are deflected in the direction of the center of said object lens.
11. The scanning electron microscope according to claim 1 , wherein
a positive voltage is applied to said detectors in order to generate a retracting electric field by which said signal electrons are retracted.
12. The scanning electron microscope according to claim 1 , wherein
a negative voltage is applied to said sample in order to generate a deceleration electric field by which said primary electrons are decelerated.
13. The scanning electron microscope according to claim 1 wherein
a negative voltage is applied to said shielding plate.
14. The scanning electron microscope according to claim 1 , wherein
said shielding plate has a ring-like upper end portion, a conical side face, and an opening portion at the lower end.
15. The scanning electron microscope according to claim 1 , wherein
said two detectors are arranged on both sides of said conductor plate, and said conductor plate and said two detectors form a plane-symmetry structure with regard to a plane including the optical axis of said scanning electron microscope.
16. The scanning electron microscope according to claim 1 , wherein
said conductor plate has a center hole as the passage of said primary electron beam and two planes with which said signal electrons collide, and
said two detectors are arranged in such a way that secondary electrons generated from said two planes may be detected.
17. The scanning electron microscope according to claim 16 , wherein
a cylindrical component is provided at the lower end of the center hole in said conductor plate.
18. An apparatus for detecting a defect, which has a scanning electron microscope and a picture display device, wherein
said scanning electron microscope has: an electron source which generates a primary electron beam; an object lens by which said primary electron beam is focused onto a sample; a conductor plate, with which signal electrons which have a high energy of 10 electron volts or more and have been generated from said sample, collide; a first and a second detectors which detect secondary electrons, which have been generated from said conductor plate; an acceleration-electric-field generating unit which generates an acceleration electric field between said object lens and said conductor plate, wherein said signal electrons are accelerated by said acceleration electric field; and a shielding plate arranged on the upper side of said object lens,
said object lens generates a leakage magnetic field by which said signal electrons are deflected in the direction of the center of said object lens, and
a positive voltage is applied to said detectors in order to generate a retracting electric field by which said signal electrons are retracted.
19. The apparatus for detecting a defect according to claim 18 , wherein
said shielding plate is an electric field shielding plate by which said acceleration electric field is controlled.
20. The apparatus for detecting a defect according to claim 18 , wherein
a negative voltage is applied to said sample in order to generate a deceleration electric field by which said primary electrons are decelerated.
21. The apparatus for detecting a defect according to claim 18 , wherein,
a negative voltage is applied to said shielding plate.
22. A method by which a sample image is obtained by use of a scanning electron microscope, having steps of:
focusing a primary electron beam from an electron source by use of an object lens to form a minute spot on a sample;
leading signal electrons generated from said sample to collide with a conductor plate;
detecting secondary electrons, which have been generated from said conductor plate, by a detector;
generating an acceleration electric field between said object lens and said conductor plate, wherein said signal electrons are accelerated by said acceleration electric field; and
arranging a shielding plate on the upper side of said object lens.
23. The method by which a sample image is obtained by use of a scanning electron microscope according to claim 22 , having steps of:
generating a deceleration electric field by applying a negative voltage to said sample, wherein said primary electrons are decelerated by said deceleration electric field; and
applying a negative voltage to said shielding plate.