The development of high-temperature stable amorphous metal alloy gates for the reduction of threshold voltage variability in short channel CMOS devices [electronic resource]
- Melody Ellen Grubbs.
- Physical description
- 1 online resource.
- Polycrystalline metal gates have replaced polycrystalline silicon gates in complementary metal oxide semiconductor (CMOS) devices for high speed performance applications. This is because the decreased capacitance caused by the gate electrode depletion layer in polycrystalline silicon gates was a pressing concern for device performance and continued scaling. Metal gates do not have this depletion issue; however, work function tuning is an issue. Consequently, a focus in the metal gate area is placed on work function engineering and the effect of processing conditions on the effective work function. The first project in this thesis studies the effect oxygen on the work function of tungsten electrodes. It is found that the presence of the meta-stable A15 phase is correlated with oxygen concentration. It is hypothesized that the observed variation in work function is due to the incorporation of oxygen from the growth environment into the W layer at the SiO2/W interface. This work shows that stochastic fluctuations in processing conditions could also cause wafer-to-wafer variability, even in long channel devices. Another concern with metal gates is that due to their polycrystalline nature, device variability could become a problem as the gate dimensions are scaled down and become comparable to the grain size since work function can vary significantly with varying grain orientation. The main project in this thesis is to develop amorphous metal gates that have the potential to reduce work function variability with respect to polycrystalline gates in nano-scale MOS devices. Thus, high temperature stable amorphous Ta40W40Si10C10 gates were developed and it is also shown that when Ta40W40Si10C10 gate electrodes are integrated in long channel transistor devices, the effective channel mobility appears to be enhanced with respect to crystalline gates.
- Publication date
- Submitted to the Department of Materials Science and Engineering.
- Ph. D. Stanford University 2011