Effect of deposition conditions and dielectric plasma treatments on the electrical properties of microcrystalline silicon TFTs

We study the growth of microcrystalline silicon films on silicon nitride as a function of the deposition conditions and the dielectric plasma treatment. For thin film transistors processed in the bottom gate configuration, we obtain stable transistors with mobilities of 0.7 cm²V^-1s^-1, indicating that we have indeed achieved a microcrystalline channel even in the bottom gate approach. Moreover, we found an opposite correlation between the linear mobility and the crystallization kinetics of the material deduced from in-situ ellipsometry measurements; i.e. the faster the crystallization kinetics, the lower the mobility. This result is discussed in terms of smaller grain size for films with fast crystallization, and is supported by Raman spectroscopy measurements. These results provide a guideline for further improving the mobility of the transistors.