The Plasma-Assisted Cleaning by Metastable-Atom Neutralization (PACMAN)
cleaning technique being developed in the Center for Plasma-Material Interactions
(CPMI) at the University of Illinois at Urbana-Champaign is a dry-non-contact
vacuum-based removal technique. The PACMAN process uses a high density helium
plasma (ne ≈ 1017m-3, Te ≈ 3eV) to achieve removal of organic contaminants on optical
masks, EUV masks, silicon wafers, and optics material used in integrated circuit
manufacturing. The PACMAN process is successful at removing both hydrocarbon
particles as well as carbon layers by utilizing the high-energy helium metastables in
the plasma. The helium metastables, with 20eV of energy, are used to break the
bonds of the particle allowing for volatilization or desorption of the atoms/hydrocarbon
chains of the particle to achieve an etching-like removal method without using traditional
etchant process gasses. With ion energies of 10eV, damage such as surface
roughening or surface erosion to the underlying structures being cleaned are avoided.
Also, film densification (the removal of hydrogen from a hydrocarbon resulting in a
dense carbon layer at the surface of the particle) is avoided in the PACMAN technique
due to the absence of high-energy ions which would preferentially sputter hydrogen out
of the particle matrix. Preliminary results for the removal of polystyrene latex nanoparticles
in the range of 30 nm to 500 nm have shown removal rates of 1.2x107 ± 5.1x105 nm3/min without damage to silicon wafers. Also, carbon films on silicon wafers have
been removed with the PACMAN technique at a rate of 3.0x106 ± 1.3x105 nm3/min.
Current results of cleaning various particle types from surfaces through the PACMAN
process will be presented in addition to a theoretical model of the removal process.