Oxidation of Silicon Implanted with High-Dose Aluminum
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Zunde Yang,* Honghua Du,*+ and Stephen P. Withrow** *Department of Materials Science and Engineering, Stevens Institute of Technology, Hoboken, NJ 07030 **Oak Ridge National Laboratory, Oak Ridge, TN 37831
ABSTRACT Si (100) wafers were implanted with Al at 500'C to high doses at multi-energies and were oxidized in I atm flowing oxygen at 1000'-1200'C. The morphology, structure, and oxidation behavior of the implanted and oxidized Si were studied using optical microscopy, atomic force microscopy, and cross-sectional transmission electron microscopy in conjunction with selected area electron diffraction and energy dispersive x-ray analysis. Large Al precipitates were formed and embedded near the surface region of the implanted Si. The oxidation rate of the Al-implanted Si wafers was lower than that of virgin Si. The unique morphology of the implanted Si results from rapid Al diffusion and segregation promoted by hot implantation. The reduction of the oxidation rate of Si by Al implantation is attributed to the preferential oxidation of Al and formation of a continuous
diffusion barrier of A12 0 3 . INTRODUCTION Oxidation studies of Si implanted with various impurities have been documented [1-4]. The list of the impurities includes Pb, Ag, Ti, Co, Fe, Sn, Ge, B, As, and P. In general, the implanted impurities give rise to an increased oxidation rate relative to that observed for unimplanted Si. The mechanism responsible for the accelerated oxidation varies depending upon the phase and structural characteristics of the implanted Si and the segregation behavior of the impurities. For example, impurities such as Pb, Ag, and Ti segregate to the vicinity of the SiO 2/Si interface during oxidation; implantation-induced lattice damage is attributed to the oxidation rate change [1]. Ge is rejected by SiO 2 and is accumulated as a Ge-rich interphase between SiO 2 and Si during oxidation, which modifies the interfacial reaction rate [2]. Impurities such as B segregate into SiO 2 during growth which increases the diffusive process in the oxide [3]. And implants such as As and P readily segregate into Si which accelerate the interfacial reaction [4]. It has been demonstrated that ion implantation provides a unique means to modify the oxidation of silicon and to study the processes responsible for the morphological and structural development during implantation and oxidation treatments. Documented studies of Al implantation of Si have focused primarily on the structural and electrical characteristics of Si [5,6]. This paper summarizes our investigation of the effect of high-dose Al implantation on the morphology, structure, and oxidation behavior of Si. The processes responsible for the morphological evolution and for the decreased oxidation rate of Al- implanted Si are discussed.
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207 Mat. Res. Soc. Symp. Proc. Vol. 354 '1995 Materials Research Society
EXPERIMENTAL Single crystal Si (100) was sequentially implanted with Al using an Extrion high-current implanter to 2.25x10' 7/cm
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