Kinetic Modeling Of Dopant And Impurity Surface Segregation During Vapor Phase Growth: Multiple Mechanism Approach
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KINETIC MODELING OF DOPANT AND IMPURITY SURFACE SEGREGATION DURING VAPOR PHASE GROWTH: MULTIPLE MECHANISM APPROACH Craig B. Arnold1 and Michael J. Aziz2 1 Materials Science and Technology Division Naval Research Laboratory, Washington, DC 20375, USA 2 Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA ABSTRACT
We propose a new kinetic model for surface segregation during vapor phase growth that accounts for multiple segregation mechanisms, including mechanisms for terrace mediated exchange and step edge mediated exchange. The major result of the model is an analytic expression for the experimentally measured segregation length and profile broadening that can be readily calculated without the need for numerical simulations. We compare the model to experimental measurements for the temperature dependence of segregation of Sb in Si(001). The model is able to accurately describe both the anomalous segregation at low temperature and the transition between equilibrium and kinetically limited segregation at high temperature. An excellent agreement is obtained using realistic energies and pre-exponential factors for the kinetic rate constants. The model can be applied to other segregating systems in planar geometries, including metallic and III-V semiconducting thin films. INTRODUCTION
Sharp interface structures have become increasingly important to advanced devices. Two relevant examples include semiconductor delta doping for quantum well devices [1, 2] and multilayered metallic systems for magnetic storage devices [3, 4]. The basic challenge in these cases is to overcome the classical problem of segregation whereby one atomic species tends to segregate to the free surface during deposition. For these advanced devices, segregation affects not only the quality of a device but also its ability to function at all. The phenomenon is general to almost any system including complex semiconductors, metals and insulators, although it has been studied most quantitatively in attempts to attain sharp doping profiles in silicon [5]. There had been extensive work on understanding the problem of segregation almost two decades ago when simple kinetic models explained important features of the early experimental results. These models predicted experimentally observed transitions from local equilibrium to kinetically trapped segregation regimes as with decreasing temperature and indicated that the only way to overcome segregation is to go to lower growth temperatures where, unfortunately, epitaxial growth tends to break down. However, it was not until the 1990’s that low-temperature epitaxial growth techniques were developed and enabled this low temperature segregation regime to be experimentally studied [6]. It was found that the previous models could not accurately describe the observed behavior at lower temperatures. Our objective is to reexamine the kinetics of segregation in light of these low temperature segregation regimes and to develop a model that successfully explains the observe
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