OBSERVATION OF SURFACE DISSOCIATION OF LOW-ENERGY POLYATOMIC IONS RELEVANT TO PLASMA PROCESSING

To gain insight into surface processes in plasma processing, basic ion beam experiments are performed on two representative polyatomic-ion s pecies: hydrocarbon ions CHx+ for deposition processes and fluorocarbo n ions CFx+ for etching processes (x = 1,2,...). A single ion species is extracted from an inductive plasma via a mass filter and directed o nto aluminum surfaces at energies < 150 eV. Significant charge neutral ization is observed which leads to backscattering of similar to 0.3% C Hx+ ions and similar to 1% CFx+ ions from the surface bombarded at 100 eV. Most of the ions scattered from the surface have kinetic energies lower than 10 eV. A polyatomic ion impinging on the surface breaks up into smaller ionic fragments. Such surface dissociation is found even at very low incident energies (10-50 eV) in the case of hydrocarbon i ons, which is attributed to vibrational excitation of the incident par ent ions. In contrast to this, fluorocarbon ions hardly dissociate at such low energies. On the other hand, at high energy (> 100 eV) incide nce of both CHx+ and CFx+ species gives rise to dissociation into smal ler fragment ions, probably via electronic excitation. (C) 1998 Americ an Vacuum Society.