Charged-particle source and method for cleaning a charged-particle source using back-sputtering

Charged-particle multi-beam apparatus for processing or inspection of a target by means of exposure with a beam of electrically charged particles, comprising:

• an illumination system, wherein the illumination system comprises
• a housing connectable to a vacuum system, allowing the charged-particle source being operated at a high vacuum,
• an emitter electrode, having an emitter surface configured to emit charged particles of a specific particle species along the direction of emission,
• a counter electrode configured to have an electrostatic voltage applied with respect to the emitter electrode at a sign opposite to that of the electrically charged particles, the counter electrode having an emitter aperture at a location downstream of the emitter surface along said direction of emission,
• a source space defined between the emitter surface and the emitter aperture,
• at least two adjustment electrodes, located surrounding the source space between the emitter electrode and the counter electrode, each adjustment electrode being configured to have a controlled electrostatic voltage applied with respect to the counter and/or emitter electrodes, and
• a pressure regulator device, said pressure regulator device controls the pressure of a gas present in the source space, wherein the pressure regulator device is configured to feed, into the source space, one or more gas species destined to be ionized during an operation in the first cleaning mode, while a voltage between the emitter and counter electrodes is applied, the particle source being operable in an emission mode wherein a voltage is applied between the emitter and counter electrodes, causing generation of charged particles leaving the particle source along the direction of emission, the particle source being further operable in a first cleaning mode wherein
• the gas is held at a pre-defined pressure value within the source space, while applying a voltage between the emitter and counter electrodes, wherein secondary electrons generated by charged particles at the counter electrode ionize particles of said gas in the source space, producing ionized gas particles and
• electrostatic potentials are applied to at least some of the adjustment electrodes, generating an electric field directing said ionized gas particles onto the emitter surfac-e
• a pattern definition device;
• and
• a projection optics system.

A charged-particle source configured for emission of electrically charged particles as a charged-particle beam along a direction of emission, said charged-particle source comprising

• a housing connectable to a vacuum system, allowing the charged-particle source being operated at a high vacuum,
• an emitter electrode, having an emitter surface configured to emit charged particles of a specific particle species along the direction of emission,
• a counter electrode configured to have an electrostatic voltage applied with respect to the emitter electrode at a sign opposite to that of the electrically charged particles, the counter electrode having an emitter aperture at a location downstream of the emitter surface along said direction of emission,
• a source space defined between the emitter surface and the emitter aperture,
• at least two adjustment electrodes, located surrounding the source space between the emitter electrode and the counter electrode, each adjustment electrode being configured to have a controlled electrostatic voltage applied with respect to the counter and/or emitter electrodes, and
• a pressure regulator device, said pressure regulator device controls the pressure of a gas present in the source space,
• the particle source being operable in an emission mode wherein a voltage is applied between the emitter and counter electrodes, causing generation of charged particles leaving the particle source along the direction of emission, the particle source being further operable in a first cleaning mode wherein
• the gas is held at a pre-defined pressure value within the source space, while applying a voltage between the emitter and counter electrodes, wherein secondary electrons generated by charged particles at the counter electrode ionize particles of said gas in the source space, producing ionized gas particles and
• electrostatic potentials are applied to at least some of the adjustment electrodes, generating an electric field directing said ionized gas particles onto the emitter surface
• and wherein the charged-particle source further comprises a gas ionizer device, said gas ionizer device being configured to irradiate energetic radiation into the source space, which energetic radiation is capable of ionizing particles of said gas present in or fed into the source space to obtain a plasma,
• the particle source being operable in a second cleaning mode wherein the gas ionizer device is operated to generate a plasma in the gas within the source space, while applying a voltage between selected ones of the adjustment electrodes so as to direct said plasma onto the emitter surface.