Yasuhiko Akamatsu

Two concerns about NBTI issue: gate dielectric scaling and increasing gate current

In order to obtain a clear perspective concerning the negative bias temperature instability (NBTI) issue toward 65-nm-node and beyond, (1) the impact of thinning gate dielectric on the basic mechanism of NBTI and (2) the influence of gate electron current on NBTI degradation rate have been investigated. Both were studied with focus on the hydrogen release reaction. This is believed to be the origin of NBTI. By studying the diffusion behavior of released hydrogen, we have clarified that our experimental results of NBTI degradation obtained under voltage-accelerated conditions can be explained by the widely accepted diffusion-controlled model without taking the influence of the gate electrode interface into account even in the case of sub-nm SiON gate dielectrics. However, from numerical calculations, it has been shown that the effect of the gate electrode interface on the diffusion behavior of released hydrogen should be taken care of at stress voltage as low as that of practical operation. In particular, the possibility of NBTI worsening due to thinning gate dielectric has been suggested especially for low stress voltage. To foresee this NBTI worsening and to evaluate NBTI lifetime precisely, we have proposed temperature-acceleration test instead of voltage-acceleration test. Next, by studying NBTI of n+gate-pMOSFET in which the influence of gate electron current is dramatically emphasized, it has been examined whether electron current flowing through gate dielectric will affect NBTI or not. Although the primary driving force of NBTI is considered to be the electric field, electron tunneling current that flows under NBT stress has been shown to worsen NBTI via the suppression of the reverse reaction of hydrogen release.

Control of Nitrogen Depth Profile and Chemical Bonding State in Silicon Oxynitride Films Formed by Radical Nitridation

Chemical bonding states and depth profiles of nitrogen in radical nitrided silicon oxide film formed in Ar/N2 plasma excited by microwave has been investigated using X-ray photoelectron spectroscopy with HF step etching. The main chemical bonding state of nitrogen atom is Si3≡N configuration, and the other unknown bonding state (termed Nhigh) is observed, whose peak energy shift is about +4.8 eV. The nitrogen atoms forming Si3≡N configuration accumulate only at the film surface and those forming Nhigh configuration are distributed deeper in the films. The Nhigh bond is very weak because it is desorbed completely at low temperature (300–500°C). Although the nitrogen atoms forming Nhigh configuration are removed by post O2-annealing, those forming Si3≡N configuration migrate toward the film/substrate interface and they increase negative bias temperature instability. In the case of ultra thin film, nitriding species forming Nhigh bond reach the film/substrate interface and form Si3≡N bond at the interface. Suppression of the generation of nitriding species forming Nhigh bond in the plasma is very important. It is clear that Nhigh bond is reduced using Ar/NH3 plasma.

V/sub ox//E/sub ox/-driven breakdown of ultra-thin SiON gate dielectric in p+gate-pMOSFET under low stress voltage of inversion mode

We have studied the breakdown mechanism of ultra-thin SiON gate dielectrics in p+gate-pMOSFETs. A systematic study with varying gate doping concentrations has revealed that, in the case of p+gate-pMOSFETs in inversion mode, gate dielectric breakdown under low stress voltage is driven by oxide voltage (V/sub ox/) or oxide field (E/sub ox/), while the breakdown under higher stress voltage is driven by gate voltage (V/sub g/). The V/sub ox//E/sub ox/-driven breakdown which emerges under low stress voltage is quite important to the reliability of low-voltage CMOS. By studying the mechanism of the breakdown, it has been clarified that the breakdown is not induced by electron current. The concept that the breakdown is due to the same mechanism as NBTI, namely the interfacial hydrogen release driven by E/sub ox/, has been shown to be possible. However, direct tunneling of holes driven by V/sub ox/ has also been found to be a possible driving force of the breakdown. Although a decisive conclusion concerning the mechanism issue has not yet been obtained, the key factor that governs the breakdown has been shown to be V/sub ox/ or E/sub ox/.

Control of nitrogen profile in radical nitridation of SiO2 films.

Advanced Technology R&D Center, Mitsubishi Electric Corporation, 8-1-1, Tsukaguchi-Honmachi, Amagasaki, Hyogo 661-8661, Japan. Phone: +81-6-6497-7545 E-mail: kawase.kazumasa@wrc.melco.co.jp Process Development Dept., Wafer Process Engineering Development Div., LSI Manufacturing Unit, Renesas Technology Corporation, 4-1, Mizuhara, Itami, Hyogo 664-0005, Japan. 3 Department of Electronic Engineering, Graduate School of Engineering, Tohoku Univ., Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579, Japan. New Industry Creation Hatchery Center, Tohoku Univ., Aoba, Aramaki, Aoba-ku, Sendai, Miyagi 980-8579, Japan.