Tilt-imaging scanning electron microscope
One embodiment relates to a tilt-imaging scanning electron microscope apparatus. The apparatus includes an electron gun, first and second deflectors, an objective electron lens, and a secondary electron detector. The first deflector deflects the electron beam away from the optical axis, and the second deflector deflects the electron beam back towards the optical axis. The objective lens focuses the electron beam onto a spot on a surface of a target substrate, wherein the electron beam lands on the surface at a tilt angle. Another embodiment relates to a method of imaging a surface of a target substrate using an electron beam with a trajectory tilted relative to a substrate surface. Other embodiments and features are also disclosed.
1. A tilt-imaging scanning electron microscope apparatus, the apparatus comprising:
an electron gun for generating an electron beam along an optical axis of an electron beam column, wherein the electron beam includes a source-energy dispersion;
a first deflector for deflecting the electron beam away from the optical axis;
a second deflector for deflecting the electron beam back towards the optical axis, wherein the second deflector is configured such that a crossover of slow and fast electrons in the electron beam is formed at a position off the optical axis between the second deflector and the objective lens;
an objective electron lens configured to image the crossover onto a spot displaced from the optical axis on a surface of a target substrate so as to generate secondary electrons, wherein the electron beam lands on the surface at a tilt angle; and
a detector for detecting the secondary electrons.
2. The apparatus of claim 1 , wherein the first and second deflectors comprise electrostatic deflectors.
3. The apparatus of claim 1 , wherein the first and second deflectors comprise magnetic deflectors.
4. The apparatus of claim 1 , wherein the objective lens comprises a magnetic section that is used to focus the electron beam onto the surface.
5. The apparatus of claim 4 , wherein the magnetic section immerses the surface in a magnetic field.
6. The apparatus of claim 4 , wherein the objective lens further comprises an electrostatic section that retards a speed of the electron beam before the electron beam reaches the surface.
7. The apparatus of claim 1 , wherein the tilt angle is relative to a normal vector for the surface, and wherein the tilt angle is non-zero.
8. The apparatus of claim 1 , wherein the first and second deflectors and the objective lens are configured to minimize an off-axis chromatic blur at the surface.
9. The apparatus of claim 1 , wherein the first and second deflectors are configured with deflections that result in a non-minimal off-axis chromatic blur at the surface in order to achieve a tilt angle that is greater than a tilt angle at a minimal off-axis chromatic blur.
10. The apparatus of claim 1 , wherein the second deflector comprises a Wien filter.
11. The apparatus of claim 10 , wherein the detector is at a fixed position, and wherein the tilt angle is configurable to four directions separated by ninety degrees.
12. The apparatus of claim 10 , wherein the Wien filter comprises an electrostatic octupole section and a magnetic quadrupole section.
13. The apparatus of claim 12 , wherein the first deflector comprises an electrostatic octupole section or a magnetic quadrupole section.
14. The apparatus of claim 13 , wherein the first deflector and the Wien filter are configured to deflect the electron beam by a same rotation angle.
15. A method of imaging a surface of a target substrate using an electron beam with a trajectory tilted relative to a substrate surface, the method comprising:
generating an electron beam along an optical axis of an electron beam column, wherein the electron beam includes a source-energy dispersion;
a first deflection by a first deflector of the electron beam away from the optical axis;
a second deflection by a second deflector of the electron beam back towards the optical axis;
forming a crossover of slow and fast electrons in the electron beam at a position off the optical axis between the second deflector and an objective lens;
imaging the crossover onto the surface of the target substrate by focusing the electron beam after the second deflection onto a spot displaced from the optical axis on a surface of a target substrate by so as to generate secondary electrons, wherein the electron beam lands on the surface at a tilt angle; and
detecting the secondary electrons.
16. The method of claim 15 further comprising:
immersing the surface of the target substrate in a magnetic field.
17. The method of claim 15 further comprising:
minimizing an off-axis chromatic blur at the surface.
18. The method of claim 15 , wherein a non-minimal off-axis chromatic blur is used to achieve a tilt angle that is greater than a tilt angle at a minimal off-axis chromatic blur.
19. The method of claim 15 , wherein the second deflection is performed by a Wien filter.