Release of light elements from ultra thin films during high resolution depth profiling using heavy ion ERDA

The modified QQDS magnetic spectrometer “Little John” [1] at the Forschungszentrum Dresden-Rossendorf is aimed to measure concentration profiles of light elements in thin layers with sub-nanometre depth resolution by Elastic Recoil Detection Analysis (ERDA). Of particular interest are various ultra thin films of metal oxides, nitrides and of carbon compounds. For these measurements heavy ions from the 5 MV-Tandem accelerator are directed to the sample. The ejected recoil atoms are detected and their energy is analysed under forward angles (15°, 30°, 45°, or 60°). Due to the low solid angle of the QQDS spectrometer of about 0.5 msr rather high fluences of initial heavy ions have to be applied. Therefore, special care must be taken to minimize layer deterioration and decomposition by preferential release of elements from the film. To identify optimum measurement conditions and perform final corrections for quantification of high resolution results, we studied the release of oxygen as a function of beam fluence. Thus, different oxides have been irradiated with Cl-, Cu- and I-ions in the energy range from 15 to 40 MeV. We could validate the earlier reported [2] dependency of oxygen loss on
• angle of incidence
• kind and energy of incoming ion
• stopping power
• layer thickness
for SiO2. Similar results have been yet found for La2O3. Further experiments on materials relevant for microelectronics as e.g. high k-dielectrics as HfO2 or ZrO2 are foreseen for the very near future and, thus, will be presented.

References: [1] H.J. Gils et al., Nucl. Instr. and Meth. A276 (1989) 151. [2] W.M. Arnoldbik et al., Nucl. Inst. and Meth. B203 (2003) 151.
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