Towards Routine Backside SIMS Sample Preparation for Efficient Support of Advanced IC Process Development

Backside Secondary Ion Mass Spectrometry (SIMS) profiling is a seemingly simple option to circumvent commonly observed depth resolution degradation in conventional front-side SIMS. However, large practical barriers in backside sample preparation prohibit a wider and more routine use of backside SIMS. Here, we explore the use of XeF(2) dry etching instead of wet etching for removal of the residual Si-substrate. The former process is essentially isotropic with similar etch rates for the different crystallographic orientations and highly selective towards the dense thermal oxide (BOX). This eliminates the need for high-precision polishing of individual samples, reducing the substrate removal to a few coarse and relatively rapid polishing steps only. Moreover, XeF(2) etching can be performed in unattended fashion and simultaneously on multiple samples, greatly increasing volume and turn-around time for backside sample preparation. Here we have explained the different practical aspects and demonstrated the feasibility of this novel approach for backside preparation for different front-end (S/D contact silicide metal, high-k metal gate) and back-end (BCD-Copper) of line applications. In conclusion, availability of a robust and reliable procedure for backside SIMS sample preparation with rapid turn-around is highly beneficial for a more efficient analytical support of advanced IC process development.