Analysis and modeling of low pressure CVD of silicon nitride from a silane-ammonia mixture - I. Experimental study and determination of a gaseous phase mechanism

This paper, Part I of two, presents the results of a study combining experi mental and modeling approaches of low pressure chemical vapor deposition (L PCVD) of silicon nitride from a silane-ammonia mixture. The experimental st udy consists in a reduced number of runs, chosen in order to identify the m ain features of the deposition process, i.e., marked nonuniformities at the wafer edge both in thickness and in Si/N composition. It is then shown tha t a complex gas-phase mechanism may be responsible for the observed physico chemical phenomena. A gaseous reaction model is thus proposed for a silane- ammonia mixture under typical low pressure CVD conditions. A complete react ion scheme is first studied. A thorough quantum Rice Ramsberger Kassel (QRR K) analysis compensated for the lack of kinetic information in the gas phas e and allowed the identification of kinetic constants for uni- and bimolecu lar reactions. Its appropriateness is examined with one-dimensional nonstea dy computations. A combined analysis of these calculations and of the QRRK results shows that the reaction model could be simplified, thus leading to a reduced reaction set reproducing the essential features of the full mecha nism experimentally observed, which involves six species with two silylamin e intermediates SiH3NH2 and SiHNH2. In Part II of this article series, this mechanism is integrated in a 2-D model of LPCVD reactors, previously devel oped in the laboratory (called CVD2) and adapted to this kind of deposition , taking into account hydrodynamics, mass transport, and chemical reactions . (C) 1999 The Electrochemical Society. S0013-4651(98)10-087-3. All rights reserved.