9 - SIMS Analysis of Wide Bandgap Semiconductors

Abstract

Secondary ion mass spectrometry (SIMS) analysis of insulators poses a special issue of charging of the dynamic surface being sputtered by the incident primary ion beam. Charging is less serious for low extraction voltage instruments such as quadrupole instruments. Mixing of atoms in the dynamic surface being sputtered by the incident energetic ions and the equilibration/stabilization time/depth are issues that must always be addressed. Depth resolution in SIMS profiles is important for defining the structure of sharp interfaces and superlattices. Often, information is desired from SIMS profiling of unwanted impurity species (elements) in various materials. Some of the common impurity species are from the ambient vacuum or heated components of materials growth machines. The same ambient vacuum species exist in a SIMS instrument. The lower the ambient vacuum, the lower the sputtered secondary ion intensities of these species. Higher the sputtering rate during SIMS profiling, lower the adsorbed density of ambient species and the lower is their sputtered secondary ion intensities. SIMS is a powerful analysis technique, but to be quantitative, a quantification system is required that relates the measured relative intensities of the secondary ions to absolute concentrations of the elements in the host matrix, as well as the accurate relative amounts of the matrix elements themselves.