Self Annealing Implantation of As + IN SILICON
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SELF ANNEALING IMPLANTATION OF As+ IN SILICON M.BERTI*, A.V.DRIGO**, R.LOTTI***, G.LULLI*** and P.G.MERLI*** * Dipartimento di Fisica "G.Galilei", GNSM-CISM, UniversitA di Padova, Via Marzolo 8 - 35131 Padova, Italy ** Dipartimento di Scienza dei Materiali, GNSM-CISM, UniversitA di Lecce, Via Arnesano - 73100 Lecce, Italy *** CNR - Istituto LAMEL, Via de' Castagnoli 1 - 40126 Bologna, Italy
ABSTRACT The structure of silicon layers implanted with high current As' beams at different power densities under self-annealing conditions (i.e. with simultaneous damage recovery activated by beam heating) has been investigated with Rutherford Backscattering and Transmission Electron Microscopy techniques. The results have been compared with previous ones obtained with P÷ implantation. They show that, in both cases, an ion-induced mechanism of recrystallization, characterized by an activation energy of the order of 0.3 eV, is operative at temperatures below the values necessary to activate thermal epitaxy. Chemical impurity profiles in samples self-annealed with As' ions at high beam power density, show the occurrence of two relevant radiation-induced effects: i) diffusion enhancement in the tail region; ii) formation of two impurity peaks, separated by a depletion region centred at the ion projected range. While the deeper peak disappears with increasing irradiation time, the one located at the maximum of nuclear energy loss grows, apparently as a consequence of segregation of As atoms at large clusters of vacancy-type defects. INTRODUCTION Dynamic annealing effects occurring in silicon during implantation at elevated temperature, have been investigated in the last years [1-91. One reason for such interest is the introduction of high-current, high energy implanters in the process of manufacturing electronic devices. In fact, due to the large beam power density, they generally cause a transient increase of wafer temperature, which may lead to partial or total recrystallization of the layer amorphized during the early stage of implantation. It is known that under irradiation, this process occurs at temperatures below the value necessary to activate Solid Phase Epitaxy (SPE) in a furnace. Experiments performed by irradiating pre-amorphized silicon layers kept at constant temperature, with various ion species [8,91 have pointed out the essential features of ion induced recrystallization which are i) activation energy of the order of 0.3 eV; ii) proportionality of the recrystallization effect to the nuclear energy loss of the implanted ion. In previous works [4,6,71 we characterized the structural evolution of thermally insulated, virgin Si samples, subjected to implantation with P+ ions at elevated beam power densities. In this paper we extend the study to self-annealing with As' ions, by using Rutherford Backscattering (RBS) and Cross Sectional Transmission Electron Microscopy (XTEM) techniques. Recrystallization data are discussed and compared with the results previously obtained with P' ions. The possibility to use RBS for mea
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