AVS 53rd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeM

Paper PS1-WeM12
In Situ Surface Diagnostics during Room Temperature Plasma Deposition of Polycrystalline Si Films

Wednesday, November 15, 2006, 11:40 am, Room 2009

Session: Plasma-Surface Interactions II
Presenter: E.S. Aydil, University of Minnesota
Authors: E.S. Aydil, University of Minnesota
R.C. Mani, Applied Materials
Correspondent: Click to Email
The ability to deposit crystalline silicon at room temperature would be very attractive for a variety of applications. Crystalline silicon films are obtained when silane is highly diluted in hydrogen, or under conditions where silane is highly dissociated such that there is high concentration of H in the gas phase. In fact, amorphous silicon films undergo disorder-to-order transition upon exposure to H atoms created by plasma dissociation of hydrogen. The mechanism of this disorder-to-order transition was uncovered recently; specifically, it was shown that hydrogen inserts into the strained bonds Si-Si bonds in amorphous silicon, and induces bond-breaking and bond re-forming reactions, which eventually lead to nucleation of crystalline silicon. This chemically-induced crystallization of silicon occurs in the temperature 150-300 C range. However, despite extensive experimental studies, unambiguous room temperature nucleation and growth of microcrystaline Si has not been demonstrated. We demonstrate the deposition of thin films containing nanocrystals of silicon using an inductively coupled plasma source and silane diluted in hydrogen at room temperature. In situ attenuated total internal reflection - Fourier transform infrared spectroscopy and in situ spectroscopic ellipsometry were used to monitor the film structure, temperature and thickness during deposition. The films were also characterized using ex-situ techniques such as Raman spectroscopy and TEM. Both in situ and ex-situ characterization techniques clearly indicated the presence of crystalline domains in the deposited films. In situ spectroscopic ellipsometry revealed that Si nanocrystals nucleate in the bulk and grow beneath an amorphous silicon crust validating the theory of hydrogen-induced crystallization. Crystals as large as 100-150 nm were observed at room temperature. Thus, silicon nanocrystals not only nucleate but also grow substantially in the bulk at room temperature.