Low voltage field emission scanning electron microscope

Claim 2

A Field Emission Gun comprising: a field emission tip for generating charged particles; a final electrode axially aligned with said field emission tip; an intermediate electrode interposed between said field emission tip and said final electrode forming a field lens with said final electrode for focusing said charged particles generated by said field emission tip; and potential means for supplying voltages to said field emission tip, said final electrode and said intermediate electrode for providing extraction, acceleration, and focus fields, said final electrode potential being lower than said intermediate electrode potential with respect to said charged particles and the ratio of said final electrode potential to said intermediate electrode potential being selected such that said field lens provides a real focus of said charged particles at a position outside of said field lens and distal of said field emission tip without further lensing, thereby producing an intense beam of low energy particles.

Claim 3

The Field Emission Gun of claim 1 wherein the charged particles are electrons extracted from said field emission tip by said extraction field.

Claim 6

The method of claim 3 wherein said charged articles are electrons.

Claim 7

The method of claim 3 wherein said charged particles are electrons extracted from said field emission tip and wherein an extraction electrode is axially aligned with And in close proximity to said field emission tip and said extraction electrode voltage is approximately 2,000 volts, said intermediate electrode voltage is approximately 2,000 volts and said final electrode potential is approximately 300 volts.

Claim 8

The method of claim 3 wherein said charged particles are electrons extracted from said field emission tip and wherein an extraction electrode is axially aligned with said field emission tip and said extraction electrode and said intermediate electrode voltage is approximately at least 500 volts.

Claim 9

The method of claim 6 wherein the said final electrode, said extraction electrode and said intermediate electrode have apertures axially aligned with said field emission tip, said final electrode and said intermediate electrode form a lens field having an axial length of approximately 2 centimeters, said extraction electrode is axially removed from said field emission tip by approximately 1 centimeter, said final electrode potential is approximately 75 volts, and said real focus occurs at a position approximately 5 centimeters from said final electrode aperature.

Claim 10

A field emission gun comprising: a field emission tip for generating electrons; a final electrode aligned with said field emission tip; an intermediate electrode aligned with said field emission tip and interposed between said field emission tip and said final electrode forming a lens with said final electrode for focusing said electrons generated by said field emission tip; an extraction electrode aligned with and in close proximity to said field emission tip providing an extraction field for drawing electrons from said field emission tip; and potential means for supplying potentials to said field emission tip, said final electrode, said intermediate electrode and said extraction electrode for generating said extraction field and acceleration and focus fields, said final electrode potential being lower than said intermediate electrode potential and the ratio of said electrode potential to said intermediate electrode potential being selected such that said lens forms a real focus of said electrons without further lensing at a position outside of said lens and distal of said field emission tip thereby producing an intense beam of low energy electrons.

Claim 11

A field emission gun comprising: a field emission tip for generating electrons; a final electrode aligned with said field emission tip; an intermediate electrode aligned with said field emission tip and interposed between said field emission tip and said final electrode forming a lens with said final electrode for focusing said electrons generated by said field emission tip; an extraction electrode aligned with and in close proximity to said field emission tip providing an extraction field for drawing electrons from said field emission tip; and potential means for supplying potentials to said field emission tip, said final electrode, said intermediate electrode and said extraction electrode for generating said extraction field and acceleration and focus fields, said final electrode potential being lower than said intermediate electrode potential and the ratio of said electrode potential to said intermediate electrode potential being selected such that said lens forms a real focus of said electrons without further lensing at a position outside of said lens and distal of said field emission tip thereby producing an intense beam of low energy electrons.

Claim 12

The Field Emission Gun of claim 8 wherein said final electrode said extraction electrode and said intermediate electrode have apertures axially aligned with said field emission tip through which said intense beam of low energy particles passes.

Claim 13

The field emission gun of claim 9 wherein said ratio is approximately 0.15.

Claim 14

The field emission gun of claim 10 wherein the extraction field intensity is at least approximately 5 times 10 7 volts per centimeter.

Claim 15

The Field Emission Gun of claim 9 wherein said intermediate electrode voltage is at least approximately 500 volts, said field lens formed by said intermediate electrode and said final electrode has an axial length of approximately 2 centimeters, and said field emission tip is axially removed from said intermediate electrode a distance of approximately at least 1 centimeter.

Claim 16

The Field Emission Gun of claim 9 including integral pumping means operatively associated with said field emission tip for providing a contamination free environment for said field emission tip.

Claim 17

The Field Emission Gun of claim 13 including a sublimation pump for reactively combining with contaminant molecules in the environment of said field emission tip, and a cryogenic chamber for cryo-pumping contaminants from said environment of said field emission tip.

Claim 18

The field emission gun of claim 13 wherein said integral pumping means comprises electrons generated by said field emission tip and emitted from said extraction electrode for ionizing molecules in the area of said field emission tip.

Claim 19

The FiEld Emission Gun of claim 9 including biasing means for establishing the potential of a specimen located at said position for preventing impingement of said intense beam on said specimen.