The effects of natural convection and conduction in a zone-melting-recrystallization chamber

Abstract

Zone-melting recrystallization (ZMR) with a graphite strip heater is used to improve the material quality of thin film structures for microelectronic applications. The process takes place in a sealed chamber filled with an inert gas such as argon or helium. The effect of natural convection and conduction at the interface between the gas and film structure was studied both numerically and experimentally. Numerical simulations of the temperature profile in the film structure, and the flow pattern and temperature field in the gas were developed. Experimental observations in a scaled setup using a liquid medium verified the flow patterns calculated from the numerical model of the gas flow in the chamber. Results indicated that the gas is stagnant in the region below the strip heater; consequently, conduction from the strip heater to the wafer is prevalent. Outside the stagnant region, natural convection cools the film structure. These two effects combine to create a steeper thermal gradient across the entire wafer which can increase the thermal stresses in the film. The magnitude of this thermal gradient depends strongly on the thermal diffusivity of the gas. The configuration of the strip heater may significantly affect the amount of heat conduction in the stagnant region.