DIFFUSION OF IODINE INTO POLYIMIDE FILMS MODIFIED BY ION-BOMBARDMENT

Polyimide films have been bombarded with a beam of Ar+ ions at different ion fluences and energies ranging from 150 keV to 1.5 MeV. We have studied the diffusion of iodine into these films by Rutherford backscattering spectrometry using a 2 MeV beam of He+ particles and we discuss the huge modifications of the diffusion profile in relation to the irradiation beam conditions. For films bombarded with a fluence of 2 x 10(14) Ar+/cm2 and different irradiation energies increasing from 150 keV to 1.5 MeV, the in-depth distribution of iodine is shown to vary in . accordance with the damage profile and to be confined in the irradiated thickness. However the RBS spectra of films irradiated at a constant energy of 150 keV indicate that the diffusion is rapidly blocked when increasing the ion fluence. Films irradiated with the same energy and ion fluence, but with different beams of rare gases, show that the diffusion is blocked at a lower fluence, when increasing the mass of the projectiles. These evolutions are interpreted by a competition between two processes: the first results from the trapping of the diffusing iodine by the radiation damage and is dominant at low fluence whereas the second one is attributed to the compaction of the irradiated layer which reduces the diffusion at high irradiation fluences. Application to the formation of diffusion barriers is proposed.