Reconsideration of hydrogen-related degradation ... - IEEE Xplore

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Therefore, negative bias temperature (NBT) stress or substrate hot electron (SHE) stress was utilized to release hydrogen from Si/SiO2 interface. As a resultĀ ...
RECONSIDERATION OF HYDROGEN-RELATED DEGRADATION MECHANISM IN GATE OXIDE Y. Mitani, T. Yamaguchi, H. Satake and A. Toriumi* Advanced LSI Technology Laboratory, Corporate R&D Center, Toshiba Corporation 8, Shinsugita-cho, Isogo-ku, Yokohama 235-8522, Japan +81-45-770-3228; fax: +81-45-770-3286; e-mail: [email protected] *Department of Materials Science, The University of Tokyo 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

ABSTRACT In this paper, we have investigated the correlation between released hydrogen from Si/SiO2 interface and trap creation in bulk SiO2. The key point of these experiments is that hydrogen release from the interface is performed without trap creation in bulk SiO2 by injected hot carriers. Therefore, negative bias temperature (NBT) stress or substrate hot electron (SHE) stress was utilized to release hydrogen from Si/SiO2 interface. As a result, SILC is clearly observed after low voltage NBT stress in pMOSFETs. In this stress condition, impact ionization at anode interface due to injected hot electrons was negligible. In the same way, SILC is also observed by applying SHE stress in nMOSFETs. In addition, the SILC is suppressed by decreasing released hydrogen using fluorine incorporation in both stress conditions. From these results, we inferred that the released hydrogen from Si/SiO2 interface strongly correlates to the trap creation in gate oxides.

ultra-thin dielectrics. Namely, as schematically shown in Fig. 1, the hydrogen-related mechanism is an origin for not only NBT degradation but also trap creation in bulk SiO2 even in the case of thicker SiO2. In the other words, almost all degradation in gate oxide might be comprehensively explained by considering the hydrogen release from Si/SiO2 interface, irrespective of oxide thickness. The objective of this work is to reinvestigate experimentally whether the released hydrogen can create the bulk traps that are the origin for the SILC, as shown in Fig. 1. In particular, we focused on the correlation between NBTI and SILC in the case of using thick SiO2 films.

[Keywords: Gate oxide, Reliability, NBTI, SILC, Hydrogen, Fluorine, Trap creation, Interface states]

FIGURE1 SCHEMATIC DIAGRAM FOR HYDROGENRELATED TRAP CREATION. CAN RELEASED H FROM SI/SIO2 INTERFACE DIFFUSE INTO SIO2 AND CREATE TRAPS?

INTRODUCTION Issues concerning the reliability of gate dielectrics constitute one of the most serious challenges in the scaling of ULSI devices. An understanding of the gate oxide degradation mechanism is essential for realizing highly reliable devices. Although the SiO2 degradation mechanism is still controversial, the hydrogen-release (HR) model [1, 2] and the anode hole injection (AHI) model [3, 4] have been proposed as acceptable SiO2 degradation mechanisms. In the HR model, released hydrogen from the anode by injected hot electrons diffuses and creates traps. On the other hand, in the AHI model, injected hot holes generated through the impact ionization at the anode attack weak spots (for example, strained Si-O bonds or Si-H bonds) and create defects in the gate oxide. It has been reported that stress-induced leakage current (SILC) and interface-state generation can be eliminated when deuterium is incorporated into gate oxides as a substitute for hydrogen [5]. On the other hand, negative bias temperature instability (NBTI) has become increasingly serious in the context of efforts to realize highly reliable integrated CMOS devices [6, 7]. NBTI is thought to be caused by the creation of interface traps following the dissociation of Si-H bonds by holes at the oxide interface, and subsequent diffusion of the released hydrogen [8, 9]. In the HR model, the AHI model and NBTI, hydrogen release process plays an important role in the deterioration of gate oxide interface and bulk. Recently, it has been suggested that oxide degradation (SILC and breakdown) and NBTI have a common origin in the case of ultra-thin (