The internal surface of cavities produced by high dose He implantation in Si are known to effectively act as gettering centres. A buried layer of cavities can thus be used to trap detrimental metal impurities before they can interact with voluntarily introduced dopants [1,2].
In the last years we used the perturbed angular correlation technique (PAC) to study the creation and development of such He-induced cavities. In order to investigate the interaction of In with cavities in Si the Bonn isotope separator was used to implant overlapping profiles of He (10 keV) and radioactive 111In (160 keV) into undoped FZ-silicon. To get insight into the cavity formation mechanism samples were prepared with various He-doses. Further, different implantation and annealing sequences were used. Typically the samples were measured directly after implantation and after different annealing steps.
We find a large fraction of 111In probe atoms subjected to an electric field gradient (EFG) corresponding to a quadrupole interaction frequency (QIF) of νQ = 411(6) MHz with η = 0.25(4). Our investigations lead us to the assumption that the Indium-atoms are situated on the inner walls of the cavities. The close similarity of the observed QIF with the QIF reported by Krausch et al. [3] for 111In on external (100) Si surfaces supports this assumption [4].To get further information we tried to incorporated 100Pd via surface diffusion and 111Ag by mass separated implantation. In both cases we were not able to see significant frequencies in the PAC-spectra. So we decided to observe the trapping of metals in the cavities indirect using 111In as a spy sitting on the inner surface. A layer of trapped metal-atoms has to change the neighborhood of the 111In-spies and therefore it should be visible in a change of the EFG. As metals we have chosen copper, silver and gold. Implantation and measurement runs were done with sequences like (1.) He-implantation, (2.) 111In-implantation, (3.) rapid thermal annealing, (4.) a first PAC-measurement, (5.) Metal(Cu,Si,Au)-implantation and (6.) finally a set of PAC-measurements after increasing annealing temperatures. The fitted results of these measurements will be available in the middle of the year 2000.
[1] S.M. Myers et al.: J. Appl. Phys. 80 (1996) 3717
[2] V. Raineri et al.: J. Appl. Phys. 78 (1995) 3727
[3] G. Krausch et al.: Surface Science 285 (1993) 81
[4] J. Bartels et al.: Hyperfine Interactions 120-121 (1999) 353