Photocathode designs and methods of generating an electron beam using a photocathode

• US 10,535,493 B2
• Filed: 10/03/2018
• Issued: 01/14/2020
• Est. Priority Date: 10/10/2017
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: KLA-Tencor Corporation
• Inventors: Ioakeimidi, Katerina, Delgado, Gildardo R., Romero, Michael E., Hill, Frances, Garcia, Rudy F.
• Primary Examiner(s): Raleigh, Donald L
• Application Number:
  US16/150,399
• Publication Number:
  US 20190108964A1
• Time in Patent Office: 468 Days
• CPC Class Codes: G02B 27/0927 Systems for changing the beam intensity distribution, e.g. Gaussian to top-hat
• CPC Class Codes: H01J 1/3044 Point emitters
• CPC Class Codes: H01J 1/34 Photo-emissive cathodes H01J1/35 takes precedence
• CPC Class Codes: H01J 19/24 Cold cathodes, e.g. field-emissive cathode
• CPC Class Codes: H01J 2201/30411 conical shaped, e.g. Spindt type
• CPC Class Codes: H01J 2201/30449 Metals and metal alloys
• CPC Class Codes: H01J 2201/3048 Semiconductor materials
• CPC Class Codes: H01J 2201/308 Semiconductor cathodes, e.g. having PN junction layers
• CPC Class Codes: H01J 2201/3423 Semiconductors, e.g. GaAs, NEA emitters
• CPC Class Codes: H01J 2201/3425 Metals, metal alloys
• CPC Class Codes: H01J 2201/3426 Alkaline metal compounds, e.g. Na-K-Sb
• CPC Class Codes: H01J 2237/06333 Photo emission
• CPC Class Codes: H01J 2237/24521 Beam diameter
• CPC Class Codes: H01J 2237/24592 Inspection and quality control of devices
• CPC Class Codes: H01J 2237/2817 Pattern inspection
• CPC Class Codes: H01J 37/06 Electron sources; Electron guns electron sources in general H01J1/02, H01J19/02; electron guns in general H01J3/02
• CPC Class Codes: H01J 37/073 Electron guns using field emission, photo emission, or secondary emission electron sources
• CPC Class Codes: H01J 37/26 Electron or ion microscopes; Electron or ion diffraction tubes
• CPC Class Codes: H01J 37/28 with scanning beams H01J37/268, H01J37/292, H01J37/2955 take precedence
• CPC Class Codes: H01J 40/06 Photo-emissive cathodes
• CPC Class Codes: H01J 40/18 : with luminescent coatings for influencing the sensitivity of the tube, e.g. by converting the input wavelength
• CPC Class Codes: H01L 21/67288 : Monitoring of warpage, curvature, damage, defects or the like

Abstract

A photocathode can include a body fabricated of a wide bandgap semiconductor material, a metal layer, and an alkali halide photocathode emitter. The body may have a thickness of less than 100 nm and the alkali halide photocathode may have a thickness less than 10 nm. The photocathode can be illuminated with a dual wavelength scheme.

Claims

1. A photocathode comprising:

a body fabricated of a wide bandgap semiconductor material, wherein the body has a first surface and a second surface opposite the first surface, and wherein the body has a thickness between the first surface and the second surface of less than 100 nm;

a metal layer disposed on the first surface, wherein the metal layer includes one or more of ruthenium or iridium; and

an alkali halide photocathode emitter disposed on the second surface, wherein the alkali halide photocathode has a thickness less than 10 nm.

2. The photocathode of claim 1, wherein the metal layer includes the ruthenium in an alloy of ruthenium and platinum.

3. The photocathode of claim 1, wherein the wide bandgap semiconductor material includes an alloy of InGaN.

4. The photocathode of claim 3, wherein the alloy of InGaN is an alloy of InGaN and GaN.

5. The photocathode of claim 1, wherein the wide bandgap semiconductor material includes an alloy of AlGaN.

6. The photocathode of claim 5, wherein the alloy of AlGaN is an alloy of AlGaN and GaN.

7. The photocathode of claim 1, wherein the wide bandgap semiconductor material includes an alloy of InGaP.

8. The photocathode of claim 7, wherein the alloy of InGaP is an alloy of InGaP and GaP.

9. The photocathode of claim 1, wherein the wide bandgap semiconductor material includes at least one of GaN and GaP.

10. The photocathode of claim 1, wherein the alkali halide photocathode includes one or more of CsI, CsBr, or CsTe.

11. The photocathode of claim 1, further comprising a cap layer disposed on the alkali halide photocathode opposite the body.

12. The photocathode of claim 11, wherein the cap layer includes one or more of ruthenium, boron, or platinum.

13. The photocathode of claim 12, wherein the cap layer includes an alloy of ruthenium and platinum.

14. An electron beam tool including the photocathode of claim 1, wherein the electron beam tool includes a detector that receives electrons generated by the electron emitter and reflected from a surface of a wafer.

15. A method comprising:

illuminating a photocathode with a photon beam having a dual wavelength scheme, wherein the photocathode includes an alkali halide photocathode disposed on a body, wherein the body is fabricated of a wide bandgap semiconductor material, wherein the body has a first surface and a second surface opposite the first surface, wherein the alkali halide photocathode emitter is disposed on the second surface, wherein the photocathode further includes a metal layer disposed on the first surface, and wherein the metal layer includes one or more of ruthenium or iridium; and

generating an electron beam as the photocathode is illuminated with the photon beam.

16. The method of claim 15, wherein the body has a thickness between the first surface and the second surface of less than 100 nm, and wherein the alkali halide photocathode has a thickness less than 10 nm.

17. The method of claim 15, wherein both wavelengths in the dual wavelength scheme are configured to pump.

18. The method of claim 15, wherein the dual wavelength scheme includes a simultaneous mode with transmission and reflection.

19. The method of claim 15, wherein the dual wavelength scheme includes a transmission mode or a reflection mode.