EXPERIMENTAL REQUIREMENTS FOR SURFACE-CHARGE SPECTROSCOPY (SCS) MEASUREMENTS - EXAMPLES OF SCS MEASUREMENTS ON HIGH-RESISTIVITY AND LOW-RESISTIVITY SI SAMPLES

The surface charge spectroscopy (SCS) method investigated by x-ray pho toelectron spectroscopy is used with structures such as semiconductors covered with a thin dielectric layer to estimate the electrical quali ty 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, i nducing imprecise or wrong results, were established. Because of the n ature of the sample, binding energy reference is one of the most impor tant points for validity of these measurements. The effects on the det ermination of the Si 2p photoelectron line position due to bad electri cal contact between the spectrometer and the semiconductor, with and w ithout its native oxide film, were studied. Surface potential modifica tions when low-energy flood gun electrons are injected into the dielec tric surface were also studied as a function of semiconductor resistiv ity. Because it is often necessary in SCS measurements to bias the sam ple, this point was also considered. Three SCS measurements are report ed, two on similar low-resistivity samples to check reproducibility of the measurements and one on a high-resistivity sample. It is shown th at the determination of the interface state density is uncertain in th e 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 condi tions. It is also pointed out that the SCS method gives information on the electrical properties of very thin dielectric film.