AN INNOVATIVE PROCESS SEQUENCE TO OBTAIN RELIABLE NITRIDED ACTIVE DIELECTRICS

Nitrided active oxides are more and more widely used in semiconductor industry for their attractive qualities in terms of reliability and re sistance to the degradation induced by current flow. Depending on the process sequence, it could happen to grow a new active dielectric in a n area on which a nitrided oxide was previously grown. Nitrogen pile-u p at the Si/SiO2 interface during the nitridation process [Y. Okada et al., J. Electrochem. Sec. 140 (1993) L87; H. Fukuda et al., in: The P hysics and Chemistry of SiO2 and the Si/SiO2 interfaces, ed. H.Z. Mass oud, E.H. Poindexter and C.R. Helms (Electrochemical Society, Penningt on, NJ, 1996) p. 15; D. Bouvet et al., J. Appl. Phys. 79 (1996) 7114] yields a modification of bulk Si surface characteristics, influencing the quality of the oxides grown subsequently to the nitrided oxide rem oval. In this paper we present an analysis of the oxide quality, repor ting their properties as a function of growing techniques (i.e., wheth er the second oxide is nitrided or not) and of first oxide removal tim e (i.e., of the overetch that the Si surface experience). Exponentiall y ramped current stress (ERCS) and constant current stress (CCS) inves tigation were performed showing that to achieve a good quality of the second dielectric a further nitridation is necessary. The quality itse lf is strictly connected to the amount of etching of the first nitride d oxide. (C) 1997 Elsevier Science B.V.