Electron and ion beam effects in auger electron spectrometry

In Auger Electron Spectrometry relatively high primary electron current density is usually used in order to obtain a good signal-to-noise ratio. As a consequence, a number of phenomena occurs, which can substantially modify—or even destroy—the sample, and impair the results of the analysis.

In this communication we report some observations on the electron and ion beam interaction on some of the insulating and conducting films used in the silicon device technology. Among the materials considered, silicon nitride and P-doped silicon dioxide are of primary interest, and will be treated in some detail; results on other films, both insulating (Al₂O₃, B-doped SiO₂, etc.) and conducting (Al-Si alloys) will also be reported.

The electron beam causes the oxides (B, Al, Si, P) to be reduced, as shown by the decrease of the height of the low energy, chemically shifted peaks (B_KVV, Al_LVV, Si_Lvv, P_Lvv) and by the contemporary increase of the height of the elemental peaks. In phosphorus doped glasses the electron beam also induces a strong surface P enrichment, followed by a P desorption. Silicon nitride was found to be quite stable against the e-b irradiation in “good” vacuum, but very sensitive to the e-b induced oxidation even at (total) pressure as low as 5 × 10¹⁰ torr. This is a very important fact to be taken into account when evaluating thin Si₃N₄ films, because it can change the apparent film stoichiometry.

Some metallic films are also preferentially oxidized by the electron beam; in Al/Si diluted alloy (0.1÷2% silicon) a strong surface silicon enrichment was found to take phase on small-grained thin films, but not on bulk material.

Our results show that much care has to be taken when performing or interpreting the AES data, and how to use, in some cases, the e-b irradiation effects to increase the sensitivity of the method.