Resolving oxidation phenomena in layered semiconductors and scaled heterogeneous integration for low-power electronics

Efficient materials development demands high-throughput experimental workflows and prompt feedback loops across all stages, from materials growth to device fabrication and quality control. There is a crucial need for characterisation approaches that can resolve both intricate structure-property relations at the atomic layer level and enable intelligent, cost-effective screening at high throughput. This is particularly pertinent to 2D materials, where there continue to be many unexplored layer- and stacking-dependent properties. This work details the development and implementation of a spectroscopic imaging ellipsometry (SIE) approach for the multi-scale analysis of layered semiconductors, focusing on oxidation phenomena. A versatile fitting algorithm is adapted for the rapid determination of the material’s complex dielectric function (ε), enabling optical modelling of multi-layer heterostructures. Combined with the various modes of SIE operation, it has the potential to unlock fast, high-throughput, large-area capability to better understand material stability and oxidation mechanisms, as well as accelerate process development. This methodology is adjustable to multiple material systems and advantageously agnostic to the underlying substrate, as exemplified through the analysis of HfS2, GaS, and monolayer WS2 systems. Given the facile extraction of their ε, we demonstrate the construction of optical models for accurate layer-thickness determination in partially oxidised samples. This can be scaled to the non-destructive 3D mapping of semiconductor / oxide heterostructures, from 1 μm lateral resolution to wafer-scale processing. When applied to the study of HfS2 oxidation, this methodology enables ready access to buried HfS2 layers, oxide quality, and lateral and vertical uniformity. The SIE analysis of the native oxide layer as a function of oxidation conditions reveals the large variation in thickness and optical properties achievable through fine-tuning of the reaction parameters. Moreover, operando capability is demonstrated for thermal oxidation up to 400 ◦C, providing insights into the temperature- and time-dependent nature of self-limiting oxide growth, and the trapping and eventual release of sulphur reaction products. Finally, this SIE methodology is used to inform the fabrication conditions of semiconductor / oxide heterostructures for future integration into resistive switching devices.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Chirca, Irina

Advisor dc:contributor.advisor

• Hofmann, Stephan

• 2D materials
• Oxidation
• Low-power electronics
• Spectroscopic imaging ellipsometry

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/9f1d6347-1b24-4683-bf0e-2283d4b6a629/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.113679

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/376447