RBS STUDY ON BOMBARDMENT-INDUCED REDISTRIBUTION OF COPPER IMPURITIES IN SILICON USING NEON, OXYGEN AND NITROGEN ION-BEAMS AT DIFFERENT IMPACT ANGLES

Sputter removal of thin overlayers of Cu on Si was studied using high-resolution Rutherford backscattering spectrometry (RBS). 4 keV Ne+, O2+ and N2+ ion beams were employed for bombardment at impact angles between 0° and 45° with respect to the surface normal. Depending upon the chemical nature and the impact angle of the primary ions significantly different "cross sections" for sputter removal of Cu were observed at bombardment fluences exceeding 1 × 1017 atoms/cm2. Inspection of the RBS spectra shows that the differences in sputter removal rate are largely due to differences in the internal distribution of relocated Cu atoms. Under Ne+ bombardment a "normal" behaviour is observed, i.e. within experimental accuracy the peak of the Cu distribution is located at the instantaneous surface and the width becomes smaller as the impact angle increases. By contrast, O2+ and N2+ bombardment causes segregation of Cu atoms beyond the oxide and nitride, respectively, generated by ion implantation. The large differences in the stationary Cu removal rate measured for normally incident O2+ and N2+ can be attributed to differences in the efficiency for backtransport of the impurities from the compound/substrate interface to the surface. With increasing impact angle of the O2+ beam the distribution of segregated Cu atoms becomes broader and shifts towards the surface, but efficient sputter removal takes place only at angles exceeding 30°. © 1990.