Ionizer and method for gas-cluster ion-beam formation

A gas-cluster ion beam processing apparatus for processing a workpiece by gas-cluster ion beam irradiation, comprising:

• a reduced-pressure atmosphere enclosure;
• a nozzle within the enclosure for forming a gas-cluster jet comprising a plurality of gas-clusters;
• an ionizer within the enclosure for ionizing at least a portion of the gas-clusters in the gas-cluster jet to form a gas-cluster ion beam, the ionizer comprising:
• an inlet end and an outlet end defining an ionization region through which a gas-cluster jet comprised of gas-clusters is directed along an axis, from the inlet end to the outlet end;
• and
• at least one plasma electron source for providing electrons to the ionizing region, the electrons for ionizing at least a portion of the gas-clusters to form a gas-cluster ion beam;
• acceleration means within the enclosure for accelerating said gas-cluster ion beam;
• and
• means for positioning a workpiece within the enclosure for irradiation by the accelerated gas-cluster ion beam.

A method for forming a gas-cluster ion beam comprising the steps of:

• providing a reduced pressure atmosphere enclosure;
• generating a gas-cluster jet comprised of a plurality of gas-clusters within the reduced-pressure atmosphere;
• providing an ionization region within the reduced pressure atmosphere;
• directing the gas-cluster jet through the ionization region;
• providing at least one plasma electron source near the ionization region;
• directing electrons from the at least one plasma electron source into the ionization region to ionize at least a portion of the gas-clusters in the gas-cluster jet to form a gas-cluster ion beam.

An ionizer for electron-impact ionization of a gas-cluster jet traveling along a gas-cluster jet axis, comprising:

• a first set of substantially linear rod electrodes disposed substantially parallel to and in a substantially cylindrical pattern that is substantially concentric about the gas-cluster jet axis and that has a first radius R1;
• a second set of substantially linear rod electrodes disposed substantially parallel to and in a substantially concentric cylindrical pattern about the gas-cluster jet axis, the substantially concentric cylindrical pattern having a radius R2, wherein R2 is greater than R1;
• one or more substantially linear thermionic filaments disposed substantially parallel to the gas-cluster jet axis at a distance greater than the first radius and less than the second radius;
• heating means for heating the one or more thermionic filaments to produce a thermionic electron emission;
• electrical biasing means to bias the first set of substantially linear rod electrodes with respect to the one or more thermionic filaments to perform as anode electrodes;
• electrical biasing means to bias the second set of substantially linear rod electrodes with respect to the one or more thermionic filaments to perform as electron-repeller electrodes;
• support means for mechanically supporting the first set of rod electrodes, the second set of rod electrodes, and the one or more thermionic filaments relative to the gas-cluster jet so that the gas cluster jet passes through the ionizer for at least partial ionization of the gas-cluster jet to form a gas-cluster ion beam.