A Multiscale Model of the Si LPCVD Process
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JJ3.7.1
A Multiscale Model of the Si LPCVD Process Maurizio Rondanini, Maurizio Masi, Sergio Carrà and Carlo Cavallotti Politecnico di Milano, Dept. of Chimica, Materiali e Ing. Chimica, “G. Natta” Via Mancinelli,7 I-20131 Milano, Italy ABSTRACT The Low Pressure Chemical Vapor Deposition of Si from SiH4 is an industrial process that can be used to deposit epitaxial Si at relatively low surface temperatures. Multiscale models are necessary in order to tune the operating conditions to optimize the quality of the deposited materials. In this work we present a multiscale approach meant to describe the film morphological evolution at different time and length scales. The reactor fluid dynamics and overall mass and temperature balances are solved with the finite element method. The morphological evolution of the film is investigated with 3D kinetic Monte Carlo. We have systematically investigated the dependence of the growth morphology from temperature, pressure and gas phase composition (SiH4/H2 ratio) with the aim of determining the operating parameters window that can lead to the best film morphology. We found that the presence of a significant amount of hydrogen on the surface can significantly influence the surface morphology. In particular hydrogen can be considered as the principal responsible of the transition from an order terrace step flow growth regime, which prevails at high temperatures, to a disordered 3 dimensional growth regime. It is also worth noting that our KMC simulations show that the hydrogen surface chemistry active at low temperatures is probably richer than expected, since the formation of a significant number of island on the surface dramatically increases the concentration of steps, and thus the variety of configurations by which two adsorbed H atoms can interact.
INTRODUCTION LPCVD is an appealing technique for the epitaxial growth of silicon. The slow deposition rates allow in fact a proper control of the film morphology. Moreover the opportunity, compared to other systems, to stack the wafers efficiently one parallel to the others makes the process extremely attractive from an economic point of view. LPCVD Si is today a material of particular interest not only for being the substrate on which many existing circuits are developed (e.g. microelectronics) but also and above all for new areas of technological application such as MEMS (micro-electro-mechanical-systems) and cheap solar devices. However all these technologies require a very accurate control of the material properties like surface roughness, grain size and internal structure. Being capable of predicting these properties with reasonable precision as a function of the operative conditions therefore becomes a pressing exigency. That’s why we are trying to develop a comprehensive model to study the silicon epitaxial deposition process, paying particular attention to the role of the temperature and to the influence of H adatoms on the surface morphological evolution.
JJ3.7.2
In this paper we describe the structure of this model and
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