Preparation of High-Quality Ultra-Thin Gate Dielectrics by Cat-CVD and Catalytic Anneal
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Hidekazu Satot"t , Akira Izumit and Hideki Matsumura t tJapan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan. [email protected] "t*FUJITSU Limited, 1500 Mizono, Tadocho, Kuwana-gun, Mie, 511-0192, Japan. ABSTRACT
This paper reports a feasibility of Cat-CVD system for improvement in characteristics of ultra thin gate dielectrics. Particularly, the effects of post deposition catalytic anneal (Catanneal) by using hydrogen (H2)-decomposed species or NH3-decomposed species produced by catalytic cracking of H2 or NH3, are investigated. The C-V characteristics are measured by MIS diode for the 4.5nm-thick Cat-CVD SiNX and 8nm-thick sputtered SiO2 for comparison. The small hysteresis loop is seen in the C-V curve of both SiNX and SiO 2 films as deposition. However, it is improved by the Cat-anneal using H2 or NH 3, and the hysteresis loop completely disappears from the C-V curves for both films. This result demonstrates that the Cat-anneal is a powerful technique to improve quality of insulating films, such as Cat-CVD SiNX and even sputtered SiO 2 films. In addition, the leakage current of SiN, films with 2.8nm equivalent oxide thickness is decreased by several orders of magnitude than that of the conventional thermal SiO 2 of similar EOT and the breakdown field is increased several MV/cm by Cat-anneal at 3009C. INTRODUCTION
As semiconductor devices are scaled down to deep sub-micron dimensions, the conventional processing temperatures around 9009C will be incompatible with the desired device structure. For example, the conventional high temperature process for formation of gate insulators changes the impurity profile in the substrate. Thus the gate insulator also must be prepared at low temperatures below 550°(2[1]. Therefore the lowering growth temperature of insulator films is a key for the fabrication of the future ULSI. The Cat-CVD method is a novel technique, in which deposition gases are decomposed by catalytic cracking reactions with a heated catalyzer placed near substrates so that SiNX films are deposited at substrate temperatures around 3009C without help from plasma nor photochemical excitation [2,3]. Thus, the surface of substrates and the films are not sustained plasma damage. Actually, we have already succeeded to deposit high quality SiNX films as passivation film as thick as 300nm by this method using a gas mixture of SiH 4 and NH3 [4]. When the flow rate of NH 3 exceeds over 50-100 times of that of SiH 4, nearly 121
Mat. Res. Soc. Symp. Proc. Vol. 606 © 2000 Materials Research Society
stoichiometric (Si3N4) films are formed in which hydrogen content is as low as a few at.%. Additionally, it is known that the Cat-CVD is useful not only deposition of films but also surface modification of semiconductors, such as direct nitridation of Si [5] and GaAs [6]. In the present paper, the feasibility of Cat-CVD system for improvement in characteristics of ultra-thin gate dielectrics is studied. Particularly, the effects of Cat-anneal by using the H2 de
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