Depth-profiling of implanted ²⁸Si by (alpha,alpha) and (alpha,p) reactions

Silicon nanocrystals enclosed in thin films (Si quantum dots or Si QDs) are regarded to be the cornerstone of future developments in new memory, photovoltaic and optoelectronic products. One way to synthesize these Si QDs is ion implantation in SiO2 layers followed by thermal annealing post-treatment.

Depth-profiling of these implanted Si ions can be performed by reactions induced by α-particles on 28Si. Indeed, for high incident energy, nuclear levels of 32S and 31P can be reached, and cross-sections for (α,α) and (α,p0) reactions are more intense. This can help to increase the signal for surface silicon, and therefore make distinguishing more easy between implanted Si and Si coming from the SiO2, even for low fluences.

In this work, (α,α) and (α,p0) reactions are applied to study depth distributions of 70 keV 28Si+ ions implanted in 200 nm SiO2 layers with fluences of 1 × 1017 and 2 × 1017 cm−2. Analysis is performed above ER = 3864 keV to take advantage of resonances in both (α,α) and (α,p0) cross-sections. We show how (α,p0) reactions can complement results provided by resonant backscattering measurements in this complex case.