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

C+ ions at 40 keV were implanted up to 2.8 x 10(17) cm (-2) into (SiO/Si)-Si-2(001) structures (samples kept at 600 degrees C) with SiO2 thicknesses of 110, 190 and 240 nm. They were subsequently annealed at 1250 degrees C under a flux of 99% Ar and 1% O-2. 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 depthwindow 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 similar to 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 similar to 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 similar to 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.

Automated summary

This study investigated the behavior of implanted C+ ions in SiO2 with different thicknesses, revealing that the SiO2/Si interface efficiently attracts C within a capture range of about 50 nm.