Tuning gas cluster ion beam systems

A method for processing a substrate, the method comprising:

• applying, at an ionizer, a drive pulse train to an ion source to ionize a gas cluster beam and transfer the drive pulse train to the gas cluster beam;
• measuring, at a detector exposed to the gas cluster beam, a beam current synchronously with the drive pulse train;
• obtaining time-of-flight information of the clusters and the monomers in the gas cluster beam based on the beam current and the drive pulse train;
• determining size information relating to a size distribution of clusters and monomers in the gas cluster ion beam based on the time-of-flight information;
• adjusting a process parameter of the gas cluster beam based on the size information;
• and
• exposing the substrate to the gas cluster beam with the adjusted process parameter.

An apparatus comprising:

• a source chamber having a beam-line for forming a gas cluster beam;
• an ionization/acceleration chamber comprising an ionizer configured to ionize the gas cluster beam and operate in a first operating state in which the ionizer is turned ON and a second operating state in which the ionizer is turned OFF, the gas cluster beam comprising a distribution of clusters of different sizes and monomers;
• a process chamber comprising a holder for holding a detector on the beam-line and expose the detector to the gas cluster beam and a current sensor to measure a beam current generated by the gas cluster beam at the detector while changing an operating state of the ionizer;
• a processor;
• and
• a non-transitory memory storing a program to be executed in the processor, the program comprising instructions to
• obtain size information relating to a size distribution of the clusters and the monomers in the gas cluster beam based on the beam current and a timing of the changing of the operating state of the ionizer, and
• adjust a process parameter of the gas cluster beam based on the size information.