(Invited) Scavenging Kinetics of Interfacial SiO2 in HfO2/SiO2/Si Gate Stacks

SiO₂-interface layer (IL) “scavenging” in high-k gate stacks needs to be understood for the interface control as well as for further EOT scaling. A simple model that the oxygen vacancy (Vo) was involved in the scavenging was proposed, but further details have not been elucidated well.

We have studied the SiO₂-IL scavenging in HfO₂/SiO₂/Si gate stacks in UHV condition in place of metal electrode scavenging. This method has enabled us to study the diffusion and reaction in this system from the top surface without a metal gate.

In this talk, we particularly focus on the following three steps in the scavenging process.  

(1)   V_O diffusion kinetics in scavenging

This has been studied by controlling as-deposited HfO₂ stoichiometry by changing the deposition conditions.

(2)   Substrate effect on scavenging

Various types of substrates with a same gate stack have been used for the scavenging experiment.

(3)   Si diffusion kinetics in scavenging

Si out-diffusion from HfO₂/SiO₂/Si gate stacks has been investigated through the mass spectroscopy.

We present experimental results in each step. In particular, we notice that SiO₂/Si interaction may be involved in this process, as well as that the scavenging causes SiO₂-IL reduction. Furthermore, we propose an analytical model for the SiO₂-IL scavenging. Interestingly, it looks like the Deal-Grove model for Si oxidation, but coefficients are related to each other in the scavenging.  

These results are important not only for scavenging SiO₂-IL in HfO₂/SiO₂/Si stacks but also for establishing the oxide electronics, because understanding of both cation and anion kinetics in oxides is critical to control the hetero-interface characteristics.