ESR studies of defects in FN-stressed SiO2 thin films

We have applied the electron spin resonance (ESR) technique to clarify the microscopic mechanism of the degradation by the Fowler-Nordheim (FN) stress of thermally grown SiO/sub 2/ films. Conventional ESR using the continuous-wave (cw) method was utilized to identify the paramagnetic defects generated. We have observed ESR signals of the E' center in the FN-stressed SiO/sub 2/ films for both the oxide thickness (T/sub ox/) of 10 nm and 25 nm. The specific properties of the E' centers created in FN-stressed SiO/sub 2/ thin films of T/sub ox/ of 10 nm were also studied by the pulsed ESR technique. In SiO/sub 2//Si for both the T/sub ox/ of 10 nm and 25 nm, the ESR signals of the E' center have been observed after applying the FN-stress. The short phase memory time of the E' center in the FN-stressed SiO/sub 2//Si with T/sub ox/ of 10 nm is ascribed to the high local concentration of these centers.

1. Introduction

The degradation of gate-oxide is one of key factors that govern the reliability of MOS-based LSI. In Flash memory which is a non-volatile EEPROM, Fowler-Nordheim (FN) tunneling is utilized to drive electrons through oxide into floating-gate. The defects generated by the high electric field stress cause stress-induced leakage current (SILC), presumably through trap-assisted tunnelling. The accumulation of defects, eventually, leads to dielectric breakdown caused by current path which is, presumably, created by percolation of the defects. In both gate oxide and tunnelling oxide, to clarify the microscopic mechanism of the degradation, it is necessary both’ to identify the defects generated and to elucidate the spatial distribution of the defects generated.