Towards quantitative depth profiling with high spatial and high depth resolution

Nowadays, fundamental SIMS physics limits the quantitative compositional analysis of new semiconductor structures with high depth resolution and high spatial resolution. Therefore, a new concept (Zero-energy SIMS) is introduced which is based on electron beam inducted etching (EBIE) of the substrate surface and subsequent post-ionization of the volatile species by short high-power laser pulses. Silicon electron beam induced etching with SF6 as precursor species with an etching yield of 0.003 Si atoms/electron is demonstrated. Zero-energy SIMS experiments in a magnetic sector instrument with SF6 in positive mode show both electron-induced processes (ESD of fluorine) and collision-induced removal of Si atoms. These sputter events are caused by the impact of accelerated SF6 fragment anions which are formed by an electron-attachment process in the gas phase. In negative mode, a large contribution of cluster ions is observed due to the high flux of incoming polyatomic cations, formed by electron-impact ionization of SF6 molecules in the gas phase. The kinetic energy distributions of these particles are in agreement with the recombination model for cluster emission.