Pressure dependence of the Al ion energy distribution functions during filtered cathodic arc thin film growth in an Ar, O2 ambient

Charge state resolved ion energy distribution functions (IEDFs) of Al+, Al2+ and Al3+ were measured as a function of Ar pressure in the range from 5.7 x 10-5 to 2.13 Pa (0.01 to 256 Pa cm). As the pressure distance product is increased, the annihilation of the Al2+ and Al3+ populations as well as the thermalization of the Al+ ion population is observed, resulting in the formation of a close to monoenergetic beam of Al+ ions at pressure distance product of 256 Pa cm. The average charge state was reduced from 1.58 to 1.00 as the pressure distance product was increased from 0.01 to 32 Pa cm. Thermalization is also observed in an Ar/O2 mixture at 128 Pa cm, where stoichiometric γ-alumina films are grown. The IEDFs have been fitted by a shifted Maxwellian distribution. The plasma processing strategy presented here resulting in a monoenergetic Al+ plasma beam may through substrate bias potential variations enable effective tailoring of thin film properties such as density, elasticity and phase stability.