Material and interface instabilities of hafnium gate oxide

The silicon technology will continue its historical rate of advancement with the Moore´s law for at least a couple of decades. With this trend, the silicon gate oxide will be scaled down to its physical limit. Introducing a physical thicker high-κ dielectric film, such as hafnium oxide, can overcome this constraint. However, high-κ gate dielectric film still gives rise to several reliability problems. This paper reviews the recent report on the material and interface instabilities of using hafnium oxide as the MOS gate dielectric. It is found that the hafnium oxide is thermal unstable because of the decomposition of more ionic Hf-0 bond and the low crystallization temperature. On the other hand, the interface trap density of HfO₂/Si interface is very high (∼10¹² cm^-2) because of the presence of Hf-Si bonds. Yet silicon oxide/high-κ or oxynitride/high-κ stack could be a short-term solution for the emerging nanometer gate length technology.