Studies of the Early Oxidation of Silicon (111) in Atomic Oxygen
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STUDIES OF THE EARLY OXIDATION OF SILICON (111) OXYGEN*
IN ATOMIC
Bhola N. De, Jane Hruska, Jane Peterkin, Yong Zhao and John A. Woollam, Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska, Lincoln, NE 68588-0511.
INTRODUCTION With the growing interest in submicron size, integrated circuit technologies based on silicon, there is continuing attention to the study of ultrathin oxides [1-5J. A number of studies have been conducted on dry oxidation of silicon in the ultrathin regime; however, there is no general agreement on the correct oxidation mechanism. It has been evident that from studies of oxidation kinetics alone, one can not determine the exact oxidation mechanism [6]. However, by examining the dependence of growth (e.g., the growth rate of oxide) on various process parameters (e.g., the pressure or the temperature during oxide growth) one might be able to reduce the list of possible mechanisms of oxide growth. Studies of oxidation mechanisms of silicon (111) in atomic oxygen, in the ultrathin oxide regime will be discussed in this paper. Particularly, the extent of agreement of experimental results with the recently proposed Murali and Murarka theory (11 will be addressed. Analyses based on other theories will be published elsewhere. THEORIES OF OXIDATION The Deal and Grove theory of silicon oxidation has long been used as a practical model for describing thick oxides (7]. According to this theory, the oxidizing species diffuses through the oxide layer and reacts at the silicon dioxidesilicon interface. The (reaction limited) oxide growth for earlier oxidation is described by a linear equation. Murali and Murarka proposed that at extremely early stages the oxidizing species diffuses through a very thin oxide layer into the silicon substrate due to very low diffusion resistance of a thin oxide layer. Thus, the oxidation takes place over a volume (i.e., reaction zone) rather than only at the interface. At later stages when the oxide thickens, all of the oxidizing species is consumed at the interface due to an increased diffusion resistance of a thick oxide layer. Since initially the oxidation takes place over a reaction zone rather than at the interface, the rate of oxide growth becomes faster. Based on this model and some additional simplifications (see reference 1 for details) the following results were obtained. There is a critical thickness, say x* of oxide layer below which the oxide growth is given by the relationship: x = A't + B, where the constant A' is proportional to the oxygen gas pressure. For thicknesses greater than x* the growth law is given by a second linear equation: x = A"t+C, where A" is again proportional to the oxygen gas pressure. The relationship between various con* Research
supported by NASA Lewis Research Center Grant No.
NAG-3-95.
Mat. Res. Soc. Symp. Proc. Vol. 163. ©1990 Materials Research Society
966
> A" and C > B. At later stants are: A' law approximates to a parabolic equation. EXPERIMENTAL
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