A Comparative Study Between High and Low Temperature Thermally Controlled Crystallization of thin Films
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Richard D. Robinson and Ioannis N. Miaoulis* Thermal Analysis of Materials Processing Laboratory, Mechanical Engineering Department, Tufts University, Medford, MA 02155
ABSTRACT Numerical simulation of zone-melting recrystallization (ZMR) was conducted to determine the heat transfer dynamics over a wide range of temperatures. ZMR is a thermal processing technique used to recrystallize materials. Therefore, the thermal effects induced by the ZMR process critically affect the crystallization dynamics. Parametric studies indicated that the conductive heat flux from the heat source through the gas accounted for at least 15% of the total energy heating the film for materials with melting points less than 800°C. The influence of this conductive heating has been neglected in past analyses. Also, materials with higher melting points are less sensitive to changes in the heat flux from the heat source. Slight variations of thermal gradients in the film can lead to different qualities of crystal, so care must be taken when processing materials with lower melting points, since they are more sensitive to temperature variation. This paper analyzes the dominant modes of heat transfer in ZMR over a wide range of temperatures that influence the recrystallization dynamics.
INTRODUCTION Electronic materials used in thin-film microelectronic devices exhibit a wide range of melting points. These compounds include Ga (30 0C), Se (217°C), Ge (937°C), Si (1412°C), and the new III-V electronic materials InSb (535 °C), GaSh (710°C), and InP (1070°C). By design or consequence, modern material processing techniques utilize heat transfer to refine and/or reorganize the material. Consequently, their thermal processing dynamics are dependent on the heat treatment process and the thermophysical properties of all the materials in the film structure. In particular, the modes of heat transfer (conduction, convection, and radiation) in the processing chamber have different levels of influence depending on the melting point of the material. In this paper, zone-melting recrystallization (ZMR) processing of different thin films (~ljtm) on silicon substrates is investigated numerically. Moreover, the effect of the heat transfer modes on the crystallization dynamics for different thin film materials is examined. ZMR is a directional solidification process used to recrystallize amorphous or polycrystalline films into a single crystal. Typically, a lower susceptor heats the film to a temperature near its melting point. A line heater situated above the film heats a narrow region, creating a molten zone. As the line heater is scanned across the film, the material in the wake of the moving molten zone recrystallizes in the form of a single crystal. A graphite strip with a square cross section was the line heat source used in this research. The ZMR processing of silicon wafers and silicon-on-insulator (SO1) structures has been investigated by numerous individuals [1-10]. Analysis of the ZMR process revealed several different physical phenomena. In particular,
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