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Leader in Integrated ICT Hardware & Systems

Rita Mullins

Together Tyndall celebrates the winners and finalists of the 2020 Postgraduate Publication of the Year.

Despite a challenging a year, our students achieved outstanding discoveries and results as part of their PhD projects, some even opening major new possibilities in their field. 

Dr. Fatima Gunning, Senior Staff Researcher & Head of Graduate Studies at Tyndall, praised the entries, saying: “This year we had twice as many submissions for the Postgraduate Research Publication of Year. Besides lockdowns and restricted access to labs, our students excelled in their research outcomes. We also noted a number of students with exceptional publications at very early stages in their PhDs, and we couldn’t let this pass in blank, so we created a new award - the Rising Talent Award. Congratulations to all!"

Rita Mullins

Rita Mullins

Rising Talent

“Self-Limiting Temperature Window for Thermal Atomic Layer Etching of HfO2 and ZrO2 Based on the Atomic-Scale Mechanism.”

1. What encouraged you to submit your application to the 2020 Postgraduate Research Publication of the Year? 

I wanted to share my PhD research on atomic layer etch modelling with the Tyndall community as I am very proud of this work. It is also a nice addition to your CV that showcases your research achievements. 

2. What inspired you to choose the subject of your paper? 

The subject of my paper focuses on attaining a detailed atomistic understanding of the mechanism of thermal ALE of technologically important high dielectric metal oxides to replace SiO2 as a gate oxide. With the scaling of semiconductor devices, features are now required at the nm scale. SiO2 is no longer reliable as a gate oxide due to the high tunnelling leakage current through it as small thicknesses. High dielectric metal oxides allow a high drive current to be maintained, minimise leakage current and a low equivalent oxide thickness can be achieved. It is difficult to investigate ALE reactions directly using experimental techniques and atomic-level simulations using density functional theory can give deep insights into the precursor chemistry and the reactions that drive the etch of metal oxides. 

3. What’s your paper about and how did you prepare for it? What role did research excellence play in your approach?

This paper is about investigating the HF pulse on the bare surfaces of HfO2 and ZrO2 for thermal ALE. Due to the scaling of semiconductor devices, high dielectric materials such as HfO2 and ZrO2 are promising candidates to replace SiO2 as a gate oxide. Conformal nm scale feature sizes in high aspect ratio structures are difficult to achieve with traditional wet and dry chemical etch methods. Atomic layer etching permits the removal of thin films with atomic-scale precision using sequential and self-limiting surface reactions. The key aspect of the ALE process is the self-limiting modification step of the material with the first precursor to produce a thin non-volatile layer. For metal oxides, thermal ALE processes generally use HF for the surface modification step. We present the Natarajan-Elliott analysis to predict the conditions at which a self-limiting or spontaneous etch reaction becomes thermodynamically favourable. We also studied the HF adsorption on HfO2 and ZrO2 and from that predicted a theoretical etch rate for both metal oxides. This information is useful for directing experimental studies of thermal ALE.      

4. The selection for Research Publication of the Year is extremely competitive. What is your advice for those aspiring for nomination next year?

My advice would be to put your publication forward for next year’s competition. Getting research published is already a success in itself and try not to let feelings of doubt stop you from entering. The more exposure your research gets - the better and you may even win a prize! 

5. What is the single most significant support Tyndall has been able to offer you in achieving your research goals? 

My supervisor Michael Nolan, alongside my colleagues who worked on this project with me were the most significant supports in my research. I have had the opportunity to present my research at international conferences that have helped me to develop good presentation skills and meet with other researchers that work in the same field as me. The Irish Centre for High-End Computing has also been a valuable service that allows me to run my calculations on the Kay supercomputer as well as our own Tyndall rocks cluster.

Research Publication Link

Rita Mullins, Suresh Kondati Natarajan, Simon D. Elliott, and Michael Nolan, “Self-Limiting Temperature Window for Thermal Atomic Layer Etching of HfO2 and ZrO2 Based on the Atomic-Scale Mechanism”, Chemistry of Materials 2020 32 (8), 3414-3426