Laser stimulated high current density photoelectron generator and method of manufacture

An electron source for generating substantially monochromatic, modulable, shapable, high intensity electron beams upon laser light illumination comprising:

• a substrate optically transmissive to said laser light;
• an electrically conductive film deposited upon a selected region of said substrate, said film optically semitransparent to said laser light;
• a film of photoemissive substance deposited on said conductive film, said photoemissive substance selected from the group consisting of cesium antimonide, sodium potassium antimonide, cesiated gallium phosphide, cesiated gallium arsenide phosphide, cesiated and oxygenated gallium arsenide, said film of photoemissive substance operable to emit a high current density beam of electrons upon illumination by laser light;
• and
• a thick, electrically conductive, metallic coating adjacent to said selected region and in electrical and thermal contact with said electrically conductive, optically semitransparent film to form therewith a low-resistance path for conducting electrons to, and heat away from, said semitransparent film of photoemissive substance.

A method of fabricating a photoemissive cathode for high current density electron emission comprising in the order given the steps of:

• providing a transparent substrate;
• masking a portion of a selected side of said substrate;
• depositing a thick metallic coating upon all of said side of said substrate except said masked portion to create a low-resistance electrical path;
• unmasking said portion of the substrate;
• depositing an electrically conductive film over at least said portion of the substrate, said film optically semitransparent to light of predetermined wavelengths;
• depositing a layer of antimony over said electrically conductive film, and
• evaporating onto said antimony layer a material selected from the group consisting of cesium, and sodium and potassium in a specified ratio.

In a direct-write electron beam semiconductor lithography system, an improved electron beam generator comprising:

• a continuous wave (CW) injection laser operable to produce an output beam of radiation in the near infrared portion of the spectrum;
• means for modulating the current input to said injection laser at a modulation rate of at least several megahertz thereby to modulate the output beam of said laser;
• and
• a photoemissive cathode positioned for illumination by the output beam of said laser, said cathode including a film of gallium arsenide coated with cesium and oxygen, said film operable to emit a high current density beam of electrons upon illumination by said laser.

In a direct-write electron beam semiconductor lithography system, an improved electron beam generator comprising:

• a continuous wave (CW) light-emitting diode operable to produce an output beam of radiation in the near infrared portion of the spectrum;
• means for modulating the current input to said light-emitting diode at a modulation rate of at least several magahertz thereby to modulate the output beam of said light-emitting diode;
• and
• a photoemissive cathode positioned for illumination by the output beam of said light-emitting diode, said cathode including a film of gallium arsenide coated with cesium and oxygen, said film operable to emit a high current density beam of electrons upon illumination by said light-emitting diode.

In a direct-write electron beam semiconductor lithography system, an improved electron beam generator comprising:

• a continuous wave laser;
• a modulator for modulating the optical output beam of said laser at a rate of at least several megahertz;
• a photoemissive cathode positioned for illumination by the output beam of said laser, said cathode including a substrate optically transmissive to said laser light, said substrate having a back side facing in a direction to receive an optical output beam of said laser and a front side opposite said back side, an electrically conductive film deposited on a selected region of the front side of said substrate, said film optically semitransparent to said laser light, a film of photoemissive substance selected from the group consisting of cesium antimonide, sodium potassium antimonide, cesiated gallium phosphide, cesiated gallium arsenide phosphide, and cesiated and oxygenated gallium arsenide, said film being deposited on said electrically conductive, optically semitransparent film and operable to emit a high current density, rapidly modulable beam of electrons upon illumination by said laser, and a thick, electrically conductive, metallic coating adjacent to said selected region and in electrical and thermal contact with said electrically conductive, optically semitransparent film;
• and
• a light optical train positioned between said laser and said cathode and operable to produce with the output beam of said laser a pattern of laser light on said photoemissive cathode such that said film emits a high current density, rapidly modulable beam of electrons to form an electron image determined by said pattern and which is suitable for direct-write semiconductor lithography.