Structural Differences Between Cvd And Thermally Grown Amorphous SiO 2
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M. Makabe, K. Hirose, H. Ishikawa, H. Ono, A. Ishitani and J. Mizuki*, ULSI DEVICE DEVELOPMENT LABS., NEC CORPORATION, 1120,SHIMOKUZAWA,SAGAMIHARA, KANAGAWA 229, JAPAN
*FUNDAMENTAL RESEARCH LABS., NEC CORPORATION, 34, MIYUKIGAOKA, TSUKUBA, IBARAKI 305, JAPAN
ABSTRACT
The structure and density of amorphous SiO 2 films grown by chemical vapor deposition (CVD) or thermal oxidation are studied by Fourier-transform infrared (FT-IR) absorption, neutron diffraction, and Rutherford backscattering (RBS) measurements. CVD oxides, formed in an atmospheric-pressure CVD reactor with a SiH 4-0 2 gas mixture at 400 0C, are compared with thermal oxides, grown at 980 0C in H2-0 2 atmosphere. The average Si-O-Si bond angle deduced from the stretching frequency of FT-IR is found to be smaller in CVD oxides than in thermal oxides, and the density revealed by RBS measurements is found to be a little lower in CVD oxides than in thermal oxides. These differences are explained by the medium-range structural disorder revealed by FT-IR measurements as well as by neutron diffraction measurements. The medium-range structural disorder in CVD oxides is responsible for large silanol content in the oxides and is the origin in difference between CVD and thermal oxides.
INTRODUCTION
Insilicon integrated circuits, amorphous SiO 2 films are widely used as gate dielectric films and as passivation films. Itis believed that SiO 2 consists of continuous random networks of cornersharing SiO 4 tetrahedra, where these tetrahedral building blocks are linked with a bridging (Si-O-Si) bond angle to form rings which have different numbers of members. This tetrahedral network structure differs depending on the growth method and influences the properties of the Si0 2 films in MOS devices. To create high performance MOS devices, it is therefore necessary to investigate the growth-dependent structural characteristics of Si02 films. This paper reports the origin in structural difference between SiO 2 films grown by chemical vapor deposition (CVD) and those grown by thermal oxidation. EXPERIMENTAL
PROCEDURES
All oxides were fabricated on (100)-orientation p-type Czochralski silicon, 455
Mat. Res. Soc. Symp. Proc. Vol. 354 @1995 Materials Research Society
one-side-polished wafers 6 inches in diameter. CVO oxides were fabricated in an atmospheric-pressure CVD reactor by a SiH4 -O2 reaction at 4000C. Thermal oxides were grown at 98000 in a H2/O2 atmosphere. The thickness of CVD oxides was 560 nm and that of the thermal oxides was 490 nm. Infrared-absorption spectra were measured with a BIO-RAD FTS-40 Fourier-transform infrared (FT-IR) spectrometer with a resolution of 4 cm- 1. With unpolarized light incident at 30+, we could observe not only transverse-optical (TO) modes but also longitudinal-optical (LO) modes of Si-O-Si vibration which cannot be seen at normal incidence. This is possible, however, only when the film provided is sufficiently thin compared with the incoming wavelength (25 p~m 1 mm). The spectral data were obtained from each sample reference
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