High Speed and High Purity Sublimation Purification Process Development of Organic Semiconductor Materials

Abstract

Sublimation purification is the most common method for the purification of low molecular organic semiconductor materials. Purification rate enhancement and high purity production in sublimation process are required in order to increase the overall throughput of electronic devices manufacturing process. In commercially practiced sublimation purification, large amount of raw materials, which are mostly powder, are purified at once and heat transfer within powder bed in the vacuum process is very slow. For these reasons, the rate limiting step is predicted to be steps within the bed of raw material such as diffusion in solid, heat and mass transfer within the bed, and outward diffusion from particle.In this work, two materials were used as model substances for sublimation process in vertical tube chamber, one was anthracene in the non-equilibrium state and the other was pentacene in the equilibrium state. We developed the mathematical model that takes into account conjugate heat and mass transfer within the cylindrical particle bed. The sublimation rate of pentacene in the equilibrium state did not depend on bed height, considering that the sublimation rate was controlled by steps outside the bed. In contrast, the sublimation rate of anthracene in the non-equilibrium state became smaller when bed height increased, considering that the sublimation rate was controlled by steps within the bed.