Improvement of Gate Oxide Integrity Characteristics in CZ-Grown Si Crystals by H 2 annealing
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Improvement of Gate Oxide Integrity Characteristics in CZ-Grown Si Crystals by H2 annealing N. Adachi, H. Nishikawa , Y.Komatsu, H. Hourai, M. Sano and T. Shigematsu Kyushu Electronic Metal Corporation , Semiconductor Research Laboratories, 2201 Kouhoku, Kishima, Saga 849-05, Japan
ABSTRACT The mechanism of improvement in gate oxide integrity (GOI) characteristics by H2 annealing in CZ-grown Silicon wafers was investigated. Grown-in defects that are considered to degrade GOI and which can be detected correlatively as 0.1 pm level size pits appearing after SC-1 cleaning, decrease drastically by H2 annealing, while other inert gases, i.e., N2 and Ar, do not exhibit such effect. Besides, H2 annealing shrinks or extinguishes oxygen precipitates significantly, while other gases do not. On the other hand, oxygen outdiffusion is exactly the same among H2, N2 and Ar annealing. From these results, it was concluded that the dominant mechanism for GOI characteristics improvement by H2 annealing is due to decomposition of the grown-in defects having Si-O bonding by the reduction reaction between Si-O bonding and hydrogen, and not due to a mere thermal decomposition enhanced by oxygen outdiffusion. 1. INTRODUCTION As the device feature size in silicon MOS ULSI's reduces to half-a-micron or less, the gate oxide thickness becomes correspondingly smaller, and the integrity of thin gate oxide against high electric-field strength has become a serious issue. It has been known that the gate oxide integrity (GOI) depends on the crystallographic quality as well as on device fabrication process. It was reported that the gate oxide integrity depends on the crystal pulling rate in CZ growth process [1J. It is generally accepted that some sort of grown-in crystallographic defects cause anomalies in the gate oxide, resulting in GOI degradation. There have been several attempts to correlate GOI to grown-in defects such as flow patterns [2] observed after Secco etching, pits of 0.1ypm in size observed after SC-1 cleaning [3,4], microdefects observed in IR tomograph [5], and so on. These studies have aimed GOI improvement through modification of crystal growth process. Mat. Res. Soc. Symp. Proc. Vol. 262. §1992 Materials Research Society
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On the other hand, it was reported that the GOI can be improved by annealing in hydrogen ambient at high temperature (approximately 950 °C or higher ) [6] The purpose of the present work is to investigate the microscopic mechanism for GOl improvement with hydrogen (H2) annealing. It was confirmed that GOI improvement occurs remarkably with hydrogen annealing, but only marginally with annealing in other inert gas ambients such as nitrogen or argon. It was also observed that hydrogen annealing shrinks or extinguishes microdefects located in the surface vicinity (-10 Pm deep). Such shrinking or extinguishing of the defects is considered to be due to chemical reduction of oxygen-containing defects by hydrogen. 2. SILICON WAFERS AND ANNEALING PROCEDURE The silicon wafers used in this study were oriented 125m
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