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ELECTRICAL AND STRUCTURAL PROPERTIES OF CATALYTIC-NITRIDED SiO2 FILMS Akira Izumi, Hidekazu Sato and Hideki Matsumura JAIST (Japan Advanced Institute of Science and Technology) Ishikawa 923-1292, JAPAN ABSTRACT This paper reports structural and electrical properties of catalytic-nitrided silicon dioxide (SiO2) films. The surface of SiO2/Si(100) was nitrided at temperatures below 573 K. It was found that the incorporated N atoms are bound to Si atoms and O atoms and located on the top-surface of SiO2. Catalytic-nitrided SiO2 films have small amounts of Si-OH bonds and adequate resistance to boron (B) penetration. INTRODUCTION The reliability and electrical properties of ultra large-scale integrated circuits (ULSI) are strongly dependent on the quality of gate dielectric [1]. Surface nitridation of SiO2 is useful for metal-oxide-semiconductor (MOS) gate dielectric to suppress boron penetration from p+-Si gate [2]. Such treatment should be prepared at low temperatures without plasma enhancement to suppress dopant diffusion and plasma damage. Excessive nitrogen at the SiO2/Si interface may reduce the peak carrier mobility in the channel of MOS devices [3]. Therefore, top-surface nitridation of SiO2 is required for the suppression of B penetration without degradation of device. Recently, we have developed a method for the low temperature nitridation of SiO2 by catalytic-nitridation method [4]. In this method, activated nitrogen related species are produced by catalytic decomposition of NH3 on heated tungsten (W) catalyzer. Applying this technique, we have already succeeded in direct surface nitridation of Si at 473 K using NH3 gas [5]. This method is also useful for surface cleaning [6] and nitridation of GaAs [7]. Crystalline Si etching with high etch rate as high as 200 nm/min is obtained using H2 gas [8]. In this paper, we investigate the structural and electrical properties of catalytic-nitrided SiO2 films. EXPERIMENTAL Nitridation treatments were performed in a catalytic-nitridation apparatus. This apparatus is basically the same as a conventional catalytic-CVD system using a W catalyzer except for the source gases. NH3 gas was used as the nitridation gas. More precise apparatus information is found in references [5-8]. After standard chemical cleaning, Si(100) wafers were oxidized by dry O2 at 1173 K to form a SiO2 layer about 5 nm thick.

K7.8.1

Table I. Conditions of nitridation NH3 gas pressure (Pa) NH3 gas flow rate (sccm) Substrate temperature (K) Catalyzer temperature: Tcat (K) Nitridation time (min) Catalyzer - substrate distance (mm)

1.3 50 473 - 573 2073 0 - 60 60

Then a nitridation treatment was performed. Typical conditions of the surface nitridation of SiO2 are summarized in Table I. The surface conditions of samples were characterized by ex-situ x-ray photoelectron spectroscopy (XPS) measurements using monochromatic Al Kα radiation. Most of the spectra were observed at the photoelectron take-off angle θ of 35o except for angle-resolved XPS (ARXPS) measurements. The shift of signals due to electrica