Electron gun and electron microscope
An electron gun for an electron microscope or similar device includes a field emitter cathode having a field emitter protrusion extending from the output surface of a monocrystalline silicon substrate, and electrodes configured to enhance the emission of electrons from a tip portion of the field emitter protrusion to generate a primary electron beam. A contiguous TiN layer is disposed directly on at least the tip portion of the field emitter protrusion using a process that minimizes oxidation and defects in the TiN layer.
1. An electron gun including a field emitter configured to generate a primary electron beam, wherein the field emitter comprises:
a monocrystalline silicon substrate having opposing first and second surfaces and including at least one integral field emitter protrusion, the field emitter protrusion having a fixed portion integrally connected to the silicon substrate and extending from the second surface to a tip portion; and
a titanium nitride (TiN) layer hermetically disposed at least on the tip portion of the field emitter protrusion such that, during operation, electrons leaving the monocrystalline silicon substrate through the tip portion to form the primary electron beam only pass through the TiN layer, wherein the TiN layer comprises at least 75 atomic percent TiN, and wherein a portion of the TiN layer located within a radius of 100 nm from the tip portion comprises less than 10 atomic percent carbon.
2. The electron gun of claim 1 , wherein the TiN layer comprises greater than 80 atomic percent TiN.
3. The electron gun of claim 1 , wherein the monocrystalline silicon substrate is p-type doped with a doping level less than approximately 10 19 cm −3 .
4. The electron gun of claim 1 , wherein the monocrystalline silicon substrate is n-type doped with a doping level between approximately 10 15 cm −3 and approximately 10 19 cm −3 .
5. The electron gun of claim 1 , wherein the monocrystalline silicon substrate has a thickness greater than about 10 μm and is p-type doped with a doping level less than approximately 10 14 cm −3 .
6. The electron gun of claim 1 , further comprising a light source configured to illuminate the first surface of the monocrystalline silicon substrate, wherein the light source comprises one of a laser diode and a light emitting diode configured such that an emission current of the primary electron beam is controllable in proportion to an amount of light transmitted from the light source into the monocrystalline silicon substrate.
7. The electron gun of claim 1 , wherein the TiN layer has a thickness in the range of 2 nm to 150 nm.
8. The electron gun of claim 1 , wherein a portion of the TiN layer located within a radius of 100 nm from the tip portion comprises less than 10 atomic percent oxygen.
9. The electron gun of claim 1 , wherein the field emitter protrusion comprises one of a cone, a pyramid, or a rounded whisker, and wherein the tip portion of the field emitter protrusion has a lateral dimension of less than 300 nm.
10. The electron gun of claim 9 , wherein the tip portion of the field emitter protrusion has a lateral dimension greater than 10 nm.
11. The electron gun of claim 1 , wherein the field emitter protrusion comprises one of a cone, a pyramid, or a rounded whisker, and wherein the tip portion of the field emitter protrusion has a diameter of less than 300 nm.
12. The electron gun of claim 1 , wherein the field emitter is configured to operate in a reverse bias mode in which a depletion layer is generated adjacent to the second surface in response to an applied electric field.
13. The electron gun of claim 1 , wherein the field emitter further comprises:
a first dielectric layer disposed on the second surface of the monocrystalline silicon substrate adjacent to the field emitter protrusion;
a first conductive gate disposed on the first dielectric layer such that an edge of the first conductive gate is spaced from the tip portion of the field emitter protrusion by a non-zero distance;
a second dielectric layer disposed on the second surface of the first conductive gate; and
a second focusing gate disposed on the second dielectric layer such that edges of the second conductive gate are spaced from the tip portion of the field emitter protrusion by a non-zero distance;
wherein each of the thicknesses of the first and the second dielectric layers are from 500 nm to 3 μm, and the first dielectric layer is +300 nm of a height of the field emitter protrusion.
14. The electron gun of claim 1 , further comprising a plurality of the field emitter protrusions arranged in a two-dimensional periodic pattern, each of the field emitter protrusion having one of the fixed portions integrally connected to the silicon substrate and extending from the second surface to a tip portion, wherein the TiN layer is hermetically disposed at least on the tip portion of each of the plurality of field emitter protrusions.
15. The electron gun of claim 14 , wherein the field emitter further comprises:
a first dielectric layer disposed on the second surface of the monocrystalline silicon substrate adjacent to the plurality of the field emitter protrusions;
a first conductive gate disposed on the first dielectric layer such that edges of the first conductive gate are spaced from the tip portion of each of the plurality of field emitter protrusions by a non-zero distance;
a second dielectric layer disposed on the second surface of the first conductive gate; and
a second focusing gate disposed on the second dielectric layer such that edges of the second conductive gate are spaced from the tip portion of each of the plurality of field emitter protrusions by a non-zero distance;
wherein each of the thicknesses of the first and the second dielectric layers are from 500 nm to 3 μm, and the first dielectric layer is +200 nm of a nominal height of the plurality of field emitter protrusions.
16. A scanning electron microscope (SEM) comprising:
an electron gun including a field emitter configured to generate a primary electron beam;
electron optics configured to de-magnify and focus the primary electron beam onto a sample; and
a detector configured to detect at least one of back-scattered electrons and secondary electrons transmitted from the sample in response to the primary electron beam;
wherein the field emitter comprises:
a monocrystalline silicon substrate having opposing first and second surfaces and including at least one integral field emitter protrusion, the field emitter protrusion having a fixed portion integrally connected to the silicon substrate and extending from the second surface to a tip portion; and
a titanium nitride (TiN) layer hermetically disposed at least on the tip portion the field emitter protrusion such that, during operation, electrons leaving the monocrystalline silicon substrate through the tip portion to form the primary electron beam only pass through the TiN layer, wherein the TiN layer comprises at least 75 atomic percent TiN, and wherein a portion of the TiN layer located within a radius of 100 nm from the tip portion comprises less than 10 atomic percent oxygen and less than 10 atomic percent carbon.
17. A device including an electron gun, the electron gun including a field emitter configured to generate a primary electron beam, wherein the field emitter comprises:
a monocrystalline silicon substrate having opposing first and second surfaces and including at least one integral field emitter protrusion, the field emitter protrusion having a fixed portion integrally connected to the silicon substrate and extending from the second surface to a tip portion; and
a titanium nitride (TiN) layer hermetically disposed at least on the tip portion the field emitter protrusion such that, during operation, electrons leaving the monocrystalline silicon substrate through the tip portion to form the primary electron beam only pass through the TiN layer, wherein the TiN layer comprises at least 75 atomic percent TiN, and wherein a portion of the TiN layer located within a radius of 100 nm from the tip portion comprises less than 10 atomic percent oxygen and less than 10 atomic percent carbon.
18. The device of claim 17 , wherein the device comprises one of a scanning electron microscope (SEM) system or an electron-beam lithography system.