Environmental Ozone Effect on the Growth of Hemispherical Grained Silicon for ULSI DRAM Stacked Capacitor

Hemispherical grained silicon (HSG Si) is a state-of-the-art method used to increase the surface area of the bottom electrode in an ultralarge-scale integration dynamic random access memory (ULSI DRAM) stacked capacitor. Since contaminants affect the formation and growth of HSG Si, the control of surface cleanliness on amorphous Si of the bottom electrode is crucial. The most critical contaminant is native oxide which forms when amorphous Si surface of the bottom electrode is exposed to air. Native oxide growth is mainly influenced by airborne ozone (O₃). In this work, it is shown that the native oxide grows linearly with exposure time to O₃. Also we show that there is a high growth rate of native oxide at a high concentration of O₃, and that HSG-Si formation in O₃ is related to crystalline quality, morphology, and reflectivity. Electrical characteristics of HSG Si are evaluated with respective O₃ conditions and a variation of capacitance is observed. Additionally, an in situ precleaning process followed by the growth of HSG Si under vacuum and implementation of O₃ chemical filters are proposed in order to control O₃.