Radiation damage evolution and its relation with dopant distribution during self-annealing implantation of As in silicon
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G. Brusatin and A. V. Drigo Dipartimento di Fisica 'G. Galilei', GNSM-CISM, Universita di Padova, Via Marzolo 8, 35131 Padova, Italy
C. Gerardi and A. Guerrieri Centro Nazionale per la Ricerca e lo Sviluppo dei Materiali, CNRSM, Via Marconi 147, 72023 Mesagne, Italy (Received 18 September 1991; accepted 18 February 1992)
The evolution of radiation damage and of dopant profiles in Si samples subjected to self-annealing implantation with 160 keV As + ions, under various transient heating conditions, depending on the beam current density, has been investigated. For temperatures in excess of 880 °C, the formation of voids is evidenced by Transmission Electron Microscopy observations. They are located in a layer extending from the surface over a depth of about 0.8 of the ion projected range, Rp (~110 nm), while extended interstitial-type defects are observed in the region below. With increasing temperature (due to increasing beam power density and/or irradiation time), voids tend to anneal in the near surface region, while they survive and grow in a region about 40 nm thick, centered at a depth of about 50 nm, where an anomalous peak in the dopant profile is developed. The annealing of the extended interstitial-type defects at depths ^Rp, which becomes appreciable for T ^ 1050 °C, is coupled to a large enhancement of dopant diffusivity in the same region. It is argued that the local vacancy supersaturation, which leads to void formation, and the corresponding interstitial excess in the deeper region, which leads to extended defect formation, are a natural consequence of the collision kinetics of the displacement process, as suggested by Monte Carlo simulations reported in the literature. The evolution of damage and the anomalies in the redistribution of dopant, observed by increasing the temperature, are described as the result of the increase in the population of mobile point defects and of their influence on the mechanism of As diffusion in the different regions of the implanted layer. I. INTRODUCTION High current ion implantation performed on thin thermally insulated wafers produces a transient increase of temperature which influences in a relevant fashion the evolution of radiation damage and the distribution of the implanted impurity in the target. Depending on several factors such as beam energy and current density, duration of the implantation, maximum temperature reached, nature of the target and of the implanted species, different phenomena may occur. The disordering action of the energetic ions, leading to damage accumulation and amorphization, is generally the dominant feature in the first stage of the process. Nevertheless, if the thermal effect of the beam leads the target to exceed the critical temperature Tcr which inhibits amorphization, epitaxial crystallization of the early amorphized layer may occur in the second stage.1 It is well known that Tcr depends on the target, the ion species, its energy, and the dose rate of implantation. At energies of the order of 200 keV and low dose rates (of the order
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