Damage-depth profiling of ion-irradiated polyimide films with a variable-energy positron beam

Various polyimide layers [2.2-2.6 mum of hexafluoroisopropylidene bis(phtha lic anhydride-oxydianiline), pyromellitic dianhydride-oxydianiline, and 3,3 '-4,4'-biphenyltetracarboxylic dianhydride-p-phenylenediamine] spin-coated on silicon substrates were studied with a variable-energy positron beam in combination with a Doppler-broadened annihilation radiation technique. From the experiments, the thickness of the layers was estimated with the VEPFIT routine. These values corresponded well to the values determined from inte rferometry and ellipsometry. Irradiation of the polyimides with 1 x 10(15) boron ions/cm(2) at an energy of 180 keV led to a strong chemical modificat ion of the irradiated top layer. This caused the inhibition of positronium formation in the irradiated layer, which was observed as a lowering of the annihilation line S parameter. The thickness of the modified layer was esti mated to be 700-800 nm. This value did not agree with the ellipsometric mea surements but corresponded to the maximum implantation depth of boron ions calculated with TRIM (Transport of Ions in Matter) code. The positron resul ts appeared somewhat larger than the TRIM estimates. Reasons for these rela tions are discussed. (C) 2000 John Wiley & Sons, Inc.