How the coupling of microwave and RF energy in materials can affect solid state charge and mass transport and result in unique processing effects

Abstract

Microwave and RF fields heat materials by inducing motion of charged particles through the action of electric or magnetic forces. Consequently, internal penetration of the fields enables volumetric heating of many materials that are only sur face-heated in conventional furnaces. This volumetric heating can accelerate endothermic reactions that are rate-limited by heat transport from the material's surface in conventional processing. The inverted temperature profiles that result from volumetric heating can provide unique processing effects. Conventional heating can result in the surface reaction completing before the interior is fully reacted. Surface pores may close prematurely, preventing mass transport of gas reactants to the center needed to complete the reaction of the interior. With inverted temperature profiles, microwave-heated materials can allow the reactant gases to permeate the specimen and diffuse to the hot center until it is fully reacted. In addition to heating, electromagnetic fields can influence reactions through direct modulation of particle motion, and, in some cases, modification of mass transport. The strongest evidence includes experiments where microwave- or RF-heated data can be compared with conventionally-heated data without reliance on an exact knowledge of the internal temperature. Several examples of such data exist, including results of a comprehensive study revealing a microwave-field-induced driving force that enhances ionic transport in materials. New results indicating microwave and RF-field enhancements of annealing kinetics in B-doped Si are under investigation to advance scientific understanding and for their application value to advanced integrated circuit manufacture.