Depth profiles of Li ions implanted in the photoresist AZ111
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I. INTRODUCTION Recently we have performed a series of measurements of ion range distributions in polymers.1'5 It was shown that for the majority of the ion species, the implantation profiles follow the Ziegler, Biersack, and Littmark (ZBL)* predictions. Exceptions were the nOble gases and the light projectiles like Li, B, and F. The rare gases diffuse during and/or after the implantation while the light ions redistribute partially following the electronic damage profile. A systematic study performed with 19F and 10B has shown that there is a threshold implantation energy at which the transition from regular to nonregular profile occurs.4'5 At this energy the electronic stopping power starts to dominate the energy transfer process. It was found that the fraction of ions that does not follow the regular profile is strongly dependent on the ion mass, being 100% for the 19F case and around 12% for 10B. Finally, and despite the nonregular shape of the ion distribution, it was possible to establish, for the 10B case, some characteristic range parameters like projected range (Rp), most probable range (R), and full width at half-maximum (FWHM) distribution. Good agreement was found between the experimental results and the ZBL calculations. An earlier work1 has already shown that when 300 keV Li is implanted into epoxy resin it also distributes according to a nonregular shape. In view of the above F and B results, it seemed interesting to perform a systematic ion distribution study of Li implanted into the On leave from Universidade Federal Fluminense, Niteroi, Rio de Janeiro, Brazil. ""Permanent address: Hahn—Meitner Institut fur Kernforschung, Glienicker Str. 100, D-1000 Berlin 39, West Germany. a)
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J. Mater. Res. 3 (6), Nov/Dec 1988
http://journals.cambridge.org
AZ111 photoresist. This work was done with several aims: (a) to observe if there is a threshold energy at which the transition from regular to nonregular Li profiles occurs; (b) to establish what percentage of the implanted ions occupies nonregular places; (c) to determine if this percentage is energy dependent; and, finally, (d) to establish the range parameters characteristic of the ion-implanted distribution in order to compare with the ZBL prediction.6 Therefore, in the present work we have determined the depth distributions of 6Li implanted into AZ111 photoresist between 30 and 150 keV energy. We have used the nuclear reaction analysis (NRA) with thermal neutrons. This technique is highly sensitive for 6Li and has the advantage of giving direct information on depth distributions while producing negligible radiation damage in the sample. II. EXPERIMENTAL PROCEDURE AND RESULTS Clean silicon wafers were spin coated with the AZ111 photoresist (nominal composition C 5 H 2 O g and density p = 1.18 g/cm 3 ) of 1 /zm thickness and baked for 20 min at 150 °C. Small pieces of the wafer (s= 2 cm 2 ) were implanted with 6Li up to total fluences of 1014 atoms/cm 2 at energies of 30, 60, 90, 120, and 150 keV. The implantations were performed at room temperature w
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