Depth Profiling by SIMS to Minimize Charging Effects

So far, some trials (1)–(5) to obtain the depth profiling of impurities in insulators by SIMS have been carried out. However, they have not always been appropriate in view of accuracy because of the charging. The charging made the shape of the secondary ion energy distribution curve broaden and shift. For example, the distribution curve of 28Si+ secondary ion in SiO₂ layer of 0.6 μm thickness on Si substrate varies with the sputtering time ( t₁→ t₄ ), as shown in Fig. 1. The energy shift was about +100 eV at the beginning of the sputtering and decreased as the sputtering time passed by t₄. On the other hand, the intensity of the secondary ion increased with the reduction of the energy shift, as shown in Fig. 2. Therefore,