In Situ Deep Level Transient Spectroscopy of Defect Evolution in Silicon Following Ion Implantation at 80 K
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during implantation, how they annihilate or cluster to fonn stable defect complexes. The information that we do have is largely derived from early studies of electron irradiation using techniques such as infrared absorption. electron paramagnetic resonance (EPR), and deep-level transient spectroscopy (DLTS . More recently. DLTS has been applied to the study of defects resulting from medium and heavy ion irradiation [ 1-31. However, DLTS is almost exclusively used ex situ to measure the deep levels resulting fi-om ion irradiation at room temperature. Therefore, the observed deep levels invariably correspond to stable defect complexes that form from the interactions of mobile defects with other defects and impurities. Such interactions occur rapidly at room temperature. hence the observed state represents the final stage of defect annihilation, migration, pairing and dissociation reactions. By irradiating at liquid nitrogen temperature, where most defects are immobile, it is possible to 'freeze in' the as-implanted damage to a large extent. Using in situ DLTS. it then becomes possible to observe the evolution of defects by raising the sample temperature and measuring the changes in the DLTS spectra. In situ DLTS is complicated by the fact that the technique relies on thermally stimulated emission of carriers from deep level traps. Since the temperature affects the defects, each DLTS scan effectixely becomes an annealing step. Thus the ability of DLTS to examine defect interactions is Present address: Departmcnt of Physics. Newv Jersey Institute ol Technology. Newark NJ 07102 * Present address: SEH-America Inc. 4111 N.E. 112th Avenue, Vancouver, WA 98682 "Onleave from the Institute of Microclectronics Technology RAS. Chernogolovka, 142432 Russia 73 Mat. Res. Soc. Symp. Proc. Vol. 532 ©1998 Materials Research Society
determined by the relative activation energies for the interaction in question and for carrier emission from the corresponding defects. In particular, levels for which the activation energy for annealing is significantly less than the energy for carrier emission will never be seen by DLTS. Fortunately, this is not the case for many defects of interest, as we show below. In situ DLTS has been demonstrated in the past, but only for light ions in n-type substrates [4-6]. In this paper. we use in situ DLTS to observe defect interactions following low temperature ion irradiation with He. Si and Ge ions. EXPERIMENTAL Schottky and p-n diodes were fabricated on both p- and n-type Czochralski (Cz; [Oi]= 6-8×x10t cm -. [C.] < 101 6 cm"3) and epitaxial wafers with resistivities of 0.4-20 a2-cm. The diodes were mrounted on a sample holder which was cooled with liquid nitrogen. To achieve electrical isolation while maintaining temperature control, the diodes were attached with conducting silver paste to a thin sapphire wafer. The unbiased diodes were implanted with 0.6-5 MeV He, Si, or Ge ions to fluences of 0.3-3x 109 cm-2. The ion energy was chosen in each case so that the implanted ion profile was just within the
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