Sensitivity of CoSi2 precipitation in silicon to extra-low dopant concentrations. I. Experiment

Abstract

We demonstrate that the precipitation of cobalt disilicide phase in silicon during high-temperature (500 °C and 650 °C) implantation is noticeably affected by impurities of phosphorus and boron. Measurements of B-type CoSi2 cluster sizes and number densities as a function of implantation dose indicate that the number density of clusters progressively increases as the phosphorus concentration increases from 7 × 1011 to 8 × 1013 cm−3. A tentative explanation of these observations is proposed based on the previously suggested mechanism of precipitate nucleation, and on the results of first principles calculations summarized in Paper II, published as a follow-up paper. The results imply that utmost care is to be taken when dealing with transition metal precipitation during ion implantation into silicon because variations in the dopant content can affect the reproducibility of results even at extremely low dopant concentrations.

Effect of CoSi2Formation Process on CMOS Transistor Electrical Properties for Sub-100-nm Memory Applications

“…Another study reported that carbon implanted above a certain level (>10 15 cm 3 ) became segregated at the grain boundaries of CoSi 2 and improved the thermal stability of CoSi 2 by suppressing grain boundary movement. 17 In our experiment, however, Co agglomeration was not significantly reduced. This is not clearly understood; however, the low level of carbon dopant (∼10 13 ) might not inhibit grain boundary movement but rather suppresses dopant diffusion.…”

Sensitivity of CoSi2 precipitation in silicon to extra-low dopant concentrations. II. First-principles calculations

“…In the first part of this paper (referred below as Paper I), 1 we describe experimental findings concerning CoSi 2 precipitation during in situ cobalt ion implantation of silicon samples at high temperatures (500 and 650 C). In such experimental conditions, cobalt precipitation takes place simultaneously with implantation and demonstrates a number of unusual features 2,3 that are not observed during more common two-stage implantation-induced cluster synthesis, where the high temperature stage follows ion implantation at room temperature.…”