Ge-rich Si 1-X Ge X Nanocrystal Formation by the Oxidation of As-Deposited Thin Amorphous Si 0.7 Ge 0.3 Layer
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Ge-rich Si1-XGeX Nanocrystal Formation by the Oxidation of As-Deposited Thin Amorphous Si0.7Ge0.3 Layer Tae-Sik Yoon Research Institute of Advanced Materials, School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea Ki-Bum Kim School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea ABSTRACT Ge-rich Si1-XGeX nanocrystals are formed by the selective oxidation of Si during the dry oxidation of an amorphous Si0.7Ge0.3 layer. The oxidation kinetics of the alloy film shows the activation energies of linear and parabolic rate constants are about 1.35 and 1.02 eV, respectively, based on the model proposed by Deal and Grove. In addition, as a result of the selective oxidation of Si and Ge pile-up during the oxidation process, Ge-rich Si1-XGeX nanocrystals are formed with the size of 5.6 ± 1.7 nm and the spatial density of 3.6×1011 /cm2 at 600 oC. At higher temperature of 700 and 800 oC, the size of nanocrystal is increased to about 20 nm. The nanocrystals formation by oxidation is thought to be due to higher oxidation rate at grain boundary than at bulk grain. Therefore, the dependence of size on temperature is explained with the grain size determined by solid phase crystallization of amorphous film, oxidation rate, and grain growth. INTRODUCTION The formation of nanocrystals (or called quantum dots) with a high density and small size less than 5 nm is an essential process for the application to single electron devices [1-3]. In a previous article [4], we have showed the fabrication of a flash-type single electron memory device operating at room temperature by depositing amorphous Si0.7Ge0.3 nanocrystals with a size of ~4 nm on SiO2 substrate by low-pressure chemical vapor deposition (LPCVD). In that fabrication, 18 nm thick upper control oxide was successively formed by deposition with Si2H6 and O2 gases and subsequent annealing at 700 oC for 30 minutes in an O2 environment to improve the dielectric quality of the oxide. However, it was found that the quality of control oxide was not good enough to guarantee the stable operation of the device. In this study, we investigated the simultaneous formation of upper control oxide and nanocrystals by partial oxidation of as-deposited amorphous Si1-XGe X film. We utilized the selective oxidation of Si during the oxidation process of Si1-XGeX alloy to form the control oxide and the resulting formation of nanocrystals by the segregated Ge-rich islands. EXPERIMENTAL DETAILS The dry oxidation kinetics of the as-deposited amorphous Si0.7Ge 0.3 alloy film was first investigated. 30 nm thick amorphous Si0.7Ge0.3 alloy and amorphous Si films were deposited on 100-nm-thick thermally grown SiO2 substrate by LPCVD. The detailed information about the deposition conditions was previously reported [5]. The Si0.7Ge 0.3 film was oxidized in the
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