Thick photoresist outgassing during MeV implantation (mechanism and impact on production)

The generation of an ion beam and its impact into photoresist-masked wafers will have an adverse effect on the vacuum of an MeV ion implanter. This is particularly significant when implanting with higher energies and higher beam current through the thick photoresist. In this paper, we will present the mechanism and effects of photoresist outgassing caused by high energy ion implantation (250 KeV to 3 MeV). Due to photoresist outgassing and its effects, production usable beam current on small process chamber can be significantly limited. Photoresist outgassing from various implant conditions will be discussed. Photoresist of various thicknesses up to 4.5 μm from several vendors and both positive and negative acting resists were compared. Both ionization (electron stripping) and neutralization (electron addition) were measured as dose shift (underdose or overdose) using TW and Rs analysis. Depending on the ion species, energy and beam current, chamber pressure rises. The pressure rise could be as high as in the E-4 torr range. If the chamber pressure is kept below 3.0 E-5 torr no observable dose shift could be detected