Boron diffusion in presence of defects induced by helium implantation

Among numerous metallic impurities gettering techniques, helium implantation that leads to the formation of both defect types (interstitial and vacancy type) has been investigated. The gettering efficiency has been demonstrated for metals like Au, Ni, Cu or Fe. Moreover, dopant gettering has also been observed on these defects. Boron is of particular interest for the realisation of ultra-shallow junctions. Its interactions with interstitial type defects are widely studied in the literature. In this paper, we will focus our attention on boron diffusion in presence of He induced defects. The boron diffusion, known to be driven by interstitial mechanism, can be largely affected by the presence of cavities, which are sinks for interstitials. In this work, n-type 〈1 1 1〉 Si wafers doped at 1 × 1014 B cm−3 were implanted with helium for various doses 1-5 × 1016 He+ cm−2 and energies 40-100 keV. Boron implantation was then performed at 5 keV for a dose of 2 × 1013 B cm−2. Secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), spreading resistance profilometry and simulation with PROMIS 1.5 code were used in order to study the defect band impact on boron diffusivity and electrical activity after classical thermal treatments. The impact of various parameters on boron diffusivity, such as defect density, distance between boron profile and defect band or annealing temperature is discussed in this work.