Rapid Thermal Annealing - Theory and Practice

Abstract

Throughout the three decades since the beginnings of the integrated circuit industry in 1958, heat-treatment has been an essential part of the processing technology for annealing, oxidation, interfacial reaction, solid state diffusion and many other physical changes in the silicon and its overlayers. Despite this central role, heat-treatment has for much of this time been carried out in basically the same way, in contrast to the radical changes that have occurred in other areas, e.g. lithography, etching, epitaxy. The industry standard heat treatment is still to load a large batch of wafers, stacked vertically along a boat, into a resistively heated oven, and to heat the whole oven to temperature, controlling this by monitoring the oven temperature. The disadvantage of this technique is that the times to ramp up and down are necessarily long, both because of the large thermal masses involved, and because the indirect method of heating the wafer results in large thermal gradients and plastic deformation (slip) if rapid heating is attempted. This disadvantage has become significant in recent years because the reduced thermal processing required by modern smallgeometry processes cannot always be satisfactorily achieved by reducing temperature: and furnace times are already as short as is feasible.