Thermal stability of boron electrical activation in preamorphised ultra-shallow junctions

Abstract

We present a detailed study of the thermal stability of activated junctions as a function of the post-annealing conditions. p +/n junctions were formed by implanting 500 eV boron (1 × 10 15 cm −2) into Ge + preamorphised Si followed by solid phase epitaxial growth (SPEG) at 650 °C. Post-annealing temperatures ranged from 250 to 950 °C, with times ranging from 3 to 1800 s. Four point probe (4PP), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM) analysis were then used to investigate the evolution of boron activation, boron diffusion and of the implantation induced extended defects. During isothermal anneals in the 750–900 °C range, it is found that the sheet resistance initially increases (deactivation) and then decreases (reactivation) with rates proportional to the temperature itself. TEM results elucidate the crucial role of the extended defects in the deactivation process. On the other hand, the combination of 4PP and SIMS measurements allows to separate the respective contribution of both cluster dissolution and dopant in-diffusion to the reactivation process.