Oxygen and Iron Redistribution upon Thermal Treatment in Iron Implanted Silicon
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OXYGEN AND IRON REDISTRIBUTION UPON THERMAL TREATMENT IN IRON IMPLANTED SILICON B. PIVAC", A. BORGHESI, L. OTTOLINI -, M. GEDDO, A. PIAGGI AND A. STELLA Dipartimentodi Fisica-Universit5i di Pavia, 1-27100 Pavia, Italy Address: R. Boskovic Institute, P.O.B. 1016, YU-41000 Zagreb, Yugoslavia **Centro di Studio per ]a CristallograliaStutturale del C.N.R., 1-27100 Pavia, Italy
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ABSTRACT In order to study the iron-oxygen interaction and their redistribution in silicon, different doses of 100 keV iron ions have been implanted into CZ silicon substrates, and subsequently annealed. The redistribution of iron and oxygen upon thermal treatment in nitrogen atmosphere was monitored with SIMS and FTIR measurements. A significant gettering of iron as well as of oxygen into the layer close to the implanted surface has been found only for doses exceeding the critical fluence, therefore indicating that the structural disorder and associated lattice strain field are the main driving forces for gettering mechanism. It has been found, however, that for doses above the critical fluence not all iron ions have been trapped into the damaged region, but a significant part of them have diffused into the bulk of the material, unaffected by gettered oxygen.
INTRODUCTION Since iron is a fast diffuser in silicon, the control of silicon wafer contamination with iron during technological processes is very difficult. In order to prevent detrimental influence of metallic impurities on device performance, an intrinsic gettering procedure is often used, due to its compatibility with VLSI technology['- 3]. Although a lot of relevant facts for this kind of gettering is known and used in industrial applications, the understanding of this process is still incomplete and requires further study. The behavior of iron implanted in FZ silicon upon annealing or oxidation has been already studied[41 and the existence of a certain critical level of fluences has been found, above which the implanted layer can not be completely recovered upon subsequent thermal annealing. In order to study the oxygen influence on iron redistribution we implanted CZ wafers with various doses of iron and subsequently annealed them thermally. A systematic study with SIMS and FTIR spectroscopy is presented.
EXPERIMENT Low boron doped (101" atoms/cm 3) and mirror polished on both surfaces CZ silicon wafers of orientation were implanted with 100 keV iron ions at room temperature. Different doses in the range 6.3x 1011 to 4 .5x 10's Fe/cm2 were implanted and subsequently annealed in a dry nitrogen atmosphere at 1000 0 C for two hours. 7 The initial interstitial oxygen concentration in as-received CZ wafer was 9.8X101 atoms/cm3 (ASTM Method F 121-80). Infrared (IR) measurements were performed with FTIR Bruker 113V spectrometer at room temperature with 4 cm-1 resolution. SIMS measurements were carried out using a Cameca IMS 4 F ion microprobe. Cs+ primary ions with an accelerating voltage of +10 kV and 750 nA current intensity were used to detect oxygen in negative mode, 80-.
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