Secondary ion mass spectrometry depth profiling and simultaneous electrical investigation of MOS structures

A comparative study of the electrical behaviour of MOS structures and the composition of the oxide layer was carried out by means of secondary ion mass spectrometry depth profiling and simultaneous electrical measurements. The width of the SiSiO₂ interface region was determined for wet, dry and HCl oxide layers using a special method for definition of the virtual SiSiO₂ interface of the depth profiles. A good correlation was found between the interface region width and the electrical parameters such as fixed oxide charge density and minimum surface state density for the samples analysed. The secondary ion intensity distributions of different contaminating species show a maximum at a distance of 20–80 Å from the interface. The incorporation of chlorine during HCl oxidation was monitored and a direct identification of migrating sodium ions in the HCl oxide layers was accomplished by comparing ²³Na⁺ depth profiles before and after positive bias- temperature stress.