Electron beam generation and measurement

1. A system comprising:

a laser source that generates a laser beam;

a photocathode in a path of the laser beam, wherein the photocathode generates an electron beam upon illumination with the laser beam;

an optical array disposed in the path of the laser beam between the laser source and the photocathode, wherein the optical array is configured to provide a flat top profile to the laser beam;

a vacuum chamber in fluid communication with the photocathode;

a phosphor screen disposed in the vacuum chamber in a path of the electron beam a non-zero distance from a surface of the photocathode, wherein the phosphor screen includes phosphor powder;

a translation mechanism configured to move the phosphor screen in the vacuum chamber relative to a surface of the photocathode;

a camera configured to image the phosphor screen; and

a processor configured to determine electron energy and/or space charge effects of the electron beam using an image from the camera.

2. The system of claim 1 , wherein the laser source provides flood illumination.

3. The system of claim 1 , wherein the laser beam has a uniform distribution over a surface of the photocathode.

4. The system of claim 1 , wherein the camera is disposed outside the vacuum chamber.

5. The system of claim 1 , wherein the photocathode includes an alkali halide.

6. A wafer inspection system including the system of claim 1 .

7. A system comprising:

a laser source that generates a laser beam;

an optical array in a path of the laser beam that is configured to split the laser beam into a plurality of beamlets, wherein each of the beamlets is configured to have a flat top profile;

a photocathode in a path of the beamlets, wherein the photocathode generates electron beams upon illumination with the beamlets;

a vacuum chamber in fluid communication with the photocathode;

a phosphor screen disposed in the vacuum chamber in a path of at least one of the electron beams a non-zero distance from a surface of the photocathode, wherein the phosphor screen includes phosphor powder;

a translation mechanism configured to move the phosphor screen in the vacuum chamber relative to a surface of the photocathode;

a camera configured to image the phosphor screen; and

a processor configured to determine electron energy and/or space charge effects of the electron beam using an image from the camera.

8. The system of claim 7 , wherein the laser source provides flood illumination.

9. The system of claim 7 , wherein the beamlets have a uniform distribution over a surface of the photocathode.

10. The system of claim 7 , wherein the photocathode includes an alkali halide.

11. The system of claim 7 , wherein the camera is disposed outside the vacuum chamber.

12. A wafer inspection system including the system of claim 7 .

13. A method comprising:

directing a laser beam at a photocathode;

converting the laser beam to have a flat top profile using an optical array in a path of the laser beam;

generating an electron beam when the laser beam with the flat top profile illuminates the photocathode;

translating a phosphor screen relative to the photocathode;

directing the electron beam at the phosphor screen;

imaging the phosphor screen using a camera; and

determining, using a processor, electron energy and/or space charge effects of the electron beam using an image from the camera.

14. The method of claim 13 , further comprising generating the laser beam with a laser source.

15. The method of claim 13 , wherein the photocathode includes an alkali halide.

16. The method of claim 13 , further comprising splitting the laser beam into a plurality of laser beams using the optical array, wherein each of the laser beams has the flat top profile.

17. The method of claim 13 , further comprising:

translating the phosphor screen out of a path of the electron beam;

directing the electron beam at a semiconductor wafer; and

detecting electrons returned from a surface of the semiconductor wafer.