Evaluation of the chemical states and electrical activation of ultra-highly B-doped Si_1-xGe_x by ion implantation and subsequent nanosecond laser annealing

Given that transistor dimensions are approaching atomic scale in metal–oxide–semiconductor field-effect-transistors (MOSFETs), attaining low-contact resistivity (ρ_c) between contact-metal and Si is a primary challenge for source/drain (S/D) fabrications. To reduce ρ_c, it is necessary to increase active dopant concentration in the semiconductor region underneath the contact-metal. High-dose ion-implantation and nanosecond laser-annealing (NLA) have been intensively investigated to produce highly activated layers in S/D regions. Particularly for the B-doped SiGe layers, which are used as S/D stressor for p-MOSFETs, non-substitutional B species are generated in the highly doped films at concentrations exceeding ∼ 10²¹ cm⁻³. These non-substitutional B are electrically non-activated and thus should be minimized to reduce ρ_c. In this study, we investigated the chemical states and electrical activation in highly B-doped SiGe layer. Using X-ray photoelectron spectroscopy (XPS), we examined the substitutionality of B-atoms and identified new chemical states of Si-B and Ge-B bonds in Si 2p and Ge 3d peaks. In the B 1s spectra, electrical activation states are determined by quantifying relative area ratios of the active/inactive B peaks, which are well matched with activation rates calculated by Hall measurements. Our findings systematically explained the activation behavior of NLA-treated B-doped SiGe films in high B-concentration ranges.