Epitaxial Silicon Thin Films by Low Temperature Aluminum Induced Crystallization of Amorphous Silicon

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0910-A21-04

Epitaxial Silicon Thin Films by Low Temperature Aluminum Induced Crystallization of Amorphous Silicon Khalil Sharif1, Husam H. Abu-Safe1, Hameed A. Naseem1, William D. Brown1, Mowafak AlJassim2, and Ram Kishore3 1 Arkansas Photovoltaic Research Center, Department of Electrical Engineering, University of Arkansas, Fayetteville, AR, 72701 2 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado, 80401 3 National Physical Laboratory, Dr. K.S. Krishman Road, New Delhi-110012, India ABSTRACT Epitaxial silicon thin film growth has been achieved on crystalline silicon substrates using aluminum induced crystallization of amorphous silicon. The phenomenon of layer inversion has been utilized in this process. Silicon wafers were used as the starting crystalline structure for the grown films. After the wafer is cleaned a thin layer of aluminum (300 nm) was deposited by sputtering. This deposition was followed by 300 nm film of amorphous silicon deposited using plasma enhanced chemical vapor deposition method. After annealing the samples for 40 minutes at 525 °C, a continuous film of silicon was formed on the silicon substrate. X-ray diffraction spectrum indicated that this film has the same orientation as that of the substrate. Scanning electron microscopy cross section images showed indistinguishable interface between the substrate and the crystallized film. Cross sectional transmission electron microscopy studies of the crystallized structure showed epitaxial nature of the films. INTRODUCTION Epitaxial growth can be achieved from solid-phase, liquid-phase, and vapor-phase. Chemical vapor deposition (CVD) is the most commonly used vapor-phase method for growing epitaxial silicon films. The process was first reported by Sangster in 1957 [1, 2]. However, epitaxial growth in this process occurs at high temperatures. For example, silicon homoepitaxy which is widely used in semiconductor industry takes place at ~1000°C. This process provides high quality silicon films for microelectronic and photovoltaic devices [3]. In the field of microelectronics, the application of low temperatures during epitaxy enables the suppression of thermally activated processes, such as dopant diffusion and segregation. This suggests the need for a new method for growing epitaxial silicon that would allow for low cost and low temperature processing. One promising method for epitaxial silicon at low temperatures is by using aluminum induced crystallization (AIC) of amorphous silicon. Using this method G. Magini et. al. [4] reported epitaxial growth at 530°C. In the current effort we used (100) oriented c-Si substrate to grow epitaxial silicon films having the same orientation as that of the substrate. Samples having c-Si/Al/a-Si configuration were annealed at temperatures below 550°C and the resulting crystalline silicon thin films were examined. Epitaxial growth of the crystalline silicon thin film is evident from x-ray diffraction (XRD), cross sectional scanning electron microscopy (SEM) and, cross sectional transmiss

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