Experimental requirements for surface charge spectroscopy (SCS) measurements. Examples of SCS measurements on high‐ and low‐resistivity Si samples

The surface charge spectroscopy (SCS) method investigated by x‐ray photoelectron spectroscopy is used with structures such as semiconductors covered with a thin dielectric layer to estimate the electrical quality of the dielectric film and to determine approximately the breakdown voltage of the dielectric and the interface state density between the semiconductor and the insulator. The experimental conditions for SCS measurements were investigated and the most important error sources, inducing imprecise or wrong results, were established. Because of the nature of the sample, binding energy reference is one of the most important points for validity of these measurements. The effects on the determination of the Si 2p photoelectron line position due to bad electrical contact between the spectrometer and the semiconductor, with and without its native oxide film, were studied. Surface potential modifications when low‐energy flood gun electrons are injected into the dielectric surface were also studied as a function of semiconductor resistivity. Because it is often necessary in SCS measurements to bias the sample, this point was also considered. Three SCS measurements are reported, two on similar low‐resistivity samples to check reproducibility of the measurements and one on a high‐resistivity sample. It is shown that the determination of the interface state density is uncertain in the case of high‐resistivity samples and how confident it is possible to be in the SCS results. Two examples of erroneous experiments are also given to illustrate the consequences of inadequate experimental conditions. It is also pointed out that the SCS method gives information on the electrical properties of very thin dielectric film.