Arsenic doped buried plate characterization in deep trenches for a 0.25 μm complementary metal–oxide–semiconductor technology by chemical etching

We present examples for two-dimensional charge carrier density characterization in advanced semiconductor technologies. The analysis was performed by charge carrier density selective etching in ${\mathrm{HF:HNO}}_{\mathrm{3}}\mathrm{=1:100–1:200}$ solutions. We applied a scanning electron microscopy stereo technique for visualization of the two-dimensional etch depth distributions. Different applications of etching techniques are given. Etching of test structures involving sharp boron concentration spikes demonstrates an obtainable lateral resolution in the order of 10 nm. The dependence of the etching rate on charge carrier (dopant) density was analyzed from comparison with reference samples. For etch solutions of ${\mathrm{HF:HNO}}_{\mathrm{3}}\mathrm{=1:100},$ we found that etching starts at As densities of about ${\text{1×10}}^{17} {\mathrm{cm}}^{\mathrm{-3}}$ for fixed etch times of 10 s. Strongly enhanced etching with a nearly constant etch rate was observed for As densities above ${\text{3×10}}^{19} {\mathrm{cm}}^{\mathrm{-3}}.$ Application of the stereo scanning electron microscopy method allows two-dimensional characterization of highly B doped source-drain areas in metal–oxide–semiconductor field effect transistors. Furthermore, we performed “n-buried plate” dopant density characterization in a 0.25 μm complementary metal–oxide–semiconductor technology. To now, the application of the scanning electron microscopy stereo technique fails for low As densities of the buried plate near the deep trench. Using focused ion beam techniques at polished cross sections opens a possibility to characterize quasi-three-dimensional dopant distributions on a sub-0.25 μm level, qualitatively.