Boron Activation During Solid Phase Epitaxial Regrowth

Abstract

AbstractTo continue scaling dimensions of transistors, higher dopant concentration levels are needed for ultra-shallow contacts. Therefore studies of dopant activation have been performed in preamorphized silicon wafers with various boron implant conditions to determine the maximum achievable dopant concentrations after Solid Phase Epitaxial Regrowth (SPER) alone. In the first experiment a silicon piece was preamorphized with a 30 keV, 1×1015 cm−2 and 90 keV, 1×1015 cm−2 Si+ implant followed by a 30 keV, 1×1015 cm−2 B+ implant. Solid phase epitaxial regrowth at 500 °C indicates that boron can be activated at low temperatures. Ultra Low Energy (ULE) implants were studied in the second experiment. Silicon wafers were implanted with 2.5 keV, 1×1015 cm−2 Si+ to amorphize and then B+ was implanted at 0.5 keV in the dose range of 1×1015 to 9×1015 cm−2. Samples were annealed in the temperature range of 500 to 650 °C. High concentrations of boron make it difficult to fully regrow amorphous layers and thus yield marginal electrical properties. Much of the boron remains inactive, particularly at the higher dose implants. In both experiments Variable Angle Spectroscopic Ellipsometry (VASE) is used to measure amorphous layer thickness and Hall effect measures active boron dose. For the first experiment, Secondary Ion Mass Spectrometry (SIMS) data compares chemical dose to active dose during the regrowth process. Sheet resistance data is obtained from a four point probe for the ULE implant experiment.