Evidence of C migration in the SiO2 to the SiO2/Si interface of C-implanted structures

Highlights: • 40 keV C ions implanted into 110, 190 and 240-nm-thick SiO₂ caps on Si at 600°C • C depth-profile after 1250°C annealing by detection of recoiled C from inside SiO₂ • C peak-shift of ~50 nm toward the SiO2/Si interface • C: ~100% was in the 240 nm SiO₂-cap but ~20% migrates to form 5-nm SiC at interface • C are diluted in SiO₂; driven-force to the interface with ~50 nm of capture range C⁺ ions at 40 keV were implanted up to 2.8 × 10¹⁷ cm⁻² into SiO₂/Si(001) structures (samples kept at 600°C) with SiO₂ thicknesses of 110, 190 and 240 nm. They were subsequently annealed at 1250°C under a flux of 99% Ar and 1% O₂. Afterwards, we measured by Elastic Recoil Detection Analysis (ERDA) the C concentration along the whole SiO₂ until the Si side nearby the SiO₂/Si interface. We could probe C-recoiled within a narrow depth-window of about 35 nm, thus a combined procedure of ERDA and sequential etching steps of the SiO₂ cap was performed. After each etching step, which removed ~ 30 nm of the oxide, we calculated a normalized result, both in extension and in intensity (in relation to a standard sample). The C distribution profile for the 110 nm case is consistent with the SRIM (The Stopping and Range of Ions in Matter) simulation of implanted C into a SiO₂(110-nm)/SiC(55-nm)/Si(bulk) structure. For the 190 nm one, the measured C shows a shift of ~ 40 nm towards SiO₂/Si interface and a systematic concentration-increase from about the middle of the cap layer up to the SiO₂/Si interface. However, according to SRIM simulation, the C concentration was supposed to decrease when approaching the interface. For the 240 nm SiO₂-cap, it shows a peak-shift of ~ 50 nm towards the SiO₂/Si interface in relation to the simulation. Our results indicate that the SiO₂/Si interface efficiently attracts C within a capture range of about 50 nm from the interface. This C peak-shift in the SiO₂ towards the SiO₂/Si interface, is only consistent with diffusion models based on C dissolved in SiO₂, forming bonds with Si or O, or even C-C complexes, but not with SiC precipitation in it.