Benefits and limitations of radiatively heated susceptors

In radiatively heated single wafer reactors, suszeptors are used to control the wafer temperature. This temperature, however, might be significantly different than the suszeptor temperature. The reason is that the conductive coupling of the suszeptor to the wafer is often small, even when the wafer is placed directly on the suszeptor, and the temperature difference is then determined by the optical properties and the spectral distribution of the illumination. In this paper these temperature differences are calculated with reactor scale simulation for typical geometries. Furthermore the pattern effect is investigated whose magnitude depends on the pattern and the configuration of wafer and suszeptor. The radiation is modeled with Monte Carlo and the optical properties of the surfaces are calculated from the electromagnetic theory of thin films. A commercial system with a thick suszeptor for Si-CVD at reduced pressure serves as an example for the size of the discussed effect. The comparison of the simulation with measurements provides a model validation. Then, a typical RTP system equipped with a thin suszeptor is investigated. The configuration is identified under which the thin suszeptor leads to a reduced temperature variation in case of a changing wafer coating and in case of a pattern.