Doping of silicon with phosphorus end-terminated polymers: source characterization and dopant diffusion in SiO2

Abstract

A polystyrene homopolymer with narrow molecular weight distribution (M_n = 2.3 ± 0.3 kg mol⁻¹, Đ = 1.05 ± 0.01) and end-terminated with a phosphorus containing moiety has been used to form P δ-layers embedded into a SiO₂ matrix. The number of P atoms in the δ-layers has been stepwise increased from ∼5 × 10¹³ to ∼1.6 × 10¹⁴ atoms per cm² by repeated doping cycles. The P δ-layers have been tested as diffusion sources at temperatures ranging from 1000 to 1200 °C for different annealing times, up to 120 s. Variations of the diffusion coefficients with the annealing time have been observed and a clear dependence of diffusion coefficients on the P concentration has been highlighted. These results suggest the presence of two different P species diffusing through the SiO₂ matrix; an initially fast diffusing P compound and a slow diffusing P atom incorporated into the oxide in a bound form. Collected data provide information about P diffusion in SiO₂ that is fundamental to the development of predictive models for nanoscale doping processes based on the use of diffusion dopant sources generated by self-limiting reactions of dopant containing molecules onto deglazed or non-deglazed semiconductor substrates.