New applications of internal photoemission to determine basic MOS system parameters

Abstract

A new approach to the photoelectric phenomena taking place in the MOS system at low electric fields in the dielectric has been developed and its basic features will be presented shortly. It allows calculation of some of the MOS structure characteristics and the good agreement between these calculated characteristics and the ones taken experimentally strongly supports the validity of the approach. Based on this new approach highly sensitive photoelectric measurement methods have been worked out. Principles underlying some of these methods, as well as experimental procedures applied will be presented. In particular, the importance will be underscored of the photoelectric measurement method of the effective contact potential difference (ECPD or phiMS) between the gate and the substrate of the MOS structure. This method is the most sensitive and most accurate of the existing methods of this parameter determination. In addition to their sensitivity and accuracy, photoelectric measurement methods allow determination of the local values of some of the MOS structure electrical parameters in the regions which are small in comparison with gate dimensions. This is done by illuminating small fragments of the gate area with a focused beam of UV radiation and measuring the resulting photocurrents in the external circuit. Scanning the gate area with such a UV radiation beam of small diameter allows determination of distributions of some of the electrical parameters over the gate area. In particular, the phiMS(x,y) distributions have been determined over gate areas of Al -SiO2-Si and poly-Si - SiO2 - Si structures. The differences between these distributions will be discussed. Using similar procedures, distributions of the barrier height local values at the gate-dielectric interface EBG(x,y) and at the semiconductor-dielectric interface EBS(x,y) can be determined. Such distributions will be demonstrated and compared with the phiMS(x,y) distribution determined for the same structure. Principles underlying possible further applications of the photoelectric measurement methods will also be discussed.