INFLUENCE OF CHARGE-EXCHANGE ON ION-NEUTRAL ARRIVAL RATES IN AN ION-ASSISTED DEPOSITION SYSTEM

During ion-assisted deposition of TiN using Kaufman sources the pressu re in the substrate chamber can rise to about 10(-2) Pa. This leads to charge-exchange collisions and as a result, a component of fast neutr al atoms in the energetic beam. This paper considers the transport of 100-500 eV Ar+ or N2+ ions through a gas mixture of argon and nitrogen of known composition. Charge exchange cross sections for N2+ --> N2, Ar+ --> Ar, Ar+ --> N2, and N2+ --> Ar reactions have been used to cal culate the neutral component of the beam. The results show that the ne utral component is only weakly dependent on the primary ion energies a nd ion species. The magnitude of this component for a constant total p ressure of 3 x 10(-2) Pa varies between 10% and 60% as the partial pre ssures of nitrogen (and argon) vary between 1 and 3 x 10(-2) Pa.