Damage and recovery in boron doped silicon on insulator layers after high energy Si~+ implantation

摘要

The effects of 2 MeV Si~+ implantation on silicon-on-insulator layers uniformly doped with B at concentrations 1.0 and 1.8 x 10~(20) cm~(-3), and the kinetics of damage recovery were investigated by carrier density, mobility measurements, and transmission electron microscopy (TEM) observations. High energy implantation reduces the hole density by about 98%; the mobility is also reduced at an extent which increases with B concentration. Isochronal and isothermal annealings show that recovery of the hole density takes place in three stages: the first stage (α) is accompanied by a mobility decrease and is followed by the second stage (β) where mobility increases attaining values close to the ones of the reference undamaged samples. Mobility keeps nearly constant in the third recovery stage (γ), which takes place above 800 ℃. As a characterizing feature the mobility values for each B concentration only depend on the hole density, irrespective of the thermal history of the samples. Experiments and TEM observations allowed us to distinguish defect recovery from SiB_3 precipitation, which can take place at temperatures higher than 700 ℃. Recovery stages are discussed, and it is concluded that dissolution of B rich clusters in stage (α) modifies the concentration, or the charge state, of the defects responsible of the second (β) stage. These defects are identified as boron interstitial clusters in consideration of their mobility behavior and of the activation energy E_β for their recovery process, which results to be 3±0.2 eV.