Mechanisms and Properties of ALD Films
Lead Research Organisation:
University of Liverpool
Department Name: Engineering (Level 1)
Abstract
Atomic layer deposition is a modified version of chemical vapour deposition (CVD) which applies an inorganic thin film to a substrate in a sequential manner. Applying a material in this way, allows for very precise control of film thickness and composition. The premise of ALD is to take a CVD based process and separate the deposition process into binary, tertiary or quaternary reactions.
This study sets out to understand the mechanisms for the deposition of ALD films. As the process is inherently surface driven, understanding the surface chemistry during growth is key. This research will explore state of the art methods, for monitoring the surface chemistry during ALD processes, including the use of a Quartz crystal microbalance (QCM), in-situ spectroscopic ellipsometry, quadrupole mass spectrometry (QMS) and low energy ion scattering (LEIS).
The insights gained into ALD mechanisms will be correlated to the functional properties of the films thus, revealing process property relationships. These relationships may lead to novel insights into the field of atomic layer deposition opening innovating deposition routes and advanced material compositions.
This study sets out to understand the mechanisms for the deposition of ALD films. As the process is inherently surface driven, understanding the surface chemistry during growth is key. This research will explore state of the art methods, for monitoring the surface chemistry during ALD processes, including the use of a Quartz crystal microbalance (QCM), in-situ spectroscopic ellipsometry, quadrupole mass spectrometry (QMS) and low energy ion scattering (LEIS).
The insights gained into ALD mechanisms will be correlated to the functional properties of the films thus, revealing process property relationships. These relationships may lead to novel insights into the field of atomic layer deposition opening innovating deposition routes and advanced material compositions.
Organisations
People |
ORCID iD |
| Paul Chalker (Primary Supervisor) | |
| Benjamin Peek (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509693/1 | 01/10/2016 | 30/09/2021 | |||
| 1857737 | Studentship | EP/N509693/1 | 01/02/2017 | 31/05/2019 | Benjamin Peek |
| Description | This project explored a number of novel approaches for the deposition of metal oxides and fluorine doped metal oxide thin films using atomic layer deposition (ALD). This is all described within the PhD thesis produced at the end of the funding. The first experimental chapter of the thesis details how hydrogen peroxide adducts can be used as stable hydrogen peroxide sources when combined with trimethylaluminium, diethylzinc and tetrakis(ethylmethylamino)hafnium(IV) for the atomic layer deposition of aluminium oxide, zinc oxide and hafnium oxide. Metal oxides deposited using hydrogen peroxide adducts are shown to have improved growth rates and modified electrical properties when compared to a water based approach. Initially, aluminium oxide thin films were grown as a test bed to assess the potential of hydrogen peroxide adducts as hydrogen peroxide sources. Following this success, zinc oxide thin films were grown using hydrogen peroxide adducts. They are shown to have significantly increased sheet resistance values and different crystal morphologies when compared to films deposited using water. Hafnium oxide thin films have also been grown at low temperature using sodium percarbonate, they show enhanced growth rates when compared to water approaches. This is the first reported use of hydrogen peroxide adducts as hydrogen peroxide sources for atomic layer deposition. Analytical techniques such as thermogravimetric analysis mass spectroscopy (TGA-MS) and remote plasma optical emission spectroscopy (RP-OES) have been used to assess precursor decomposition and vapour phase composition. The second experimental chapter explores how ALD aluminium oxide can be doped with fluorine to produce thin film gate oxides which have a modified threshold voltage when incorporated into AlGaN/ GaN metal-insulator-semiconductor heterostructure field effect transistor devices. A +2.5V positive threshold voltage shift is observed in E-mode devices which may lead to safer and more energy efficient devices. Low energy ion scattering (LEIS) is used and demonstrated as a key analytical tool for the analysis of ALD thin films for the materialistic composition as well as determining potential reaction mechanisms. The final experimental chapter explains the design and fabrication of a pulsed fluidised bed deposition tool for in situ synthesis of a fluorine containing molecule. The in situ synthesis allows for controlled spatial fluorine doping of ALD aluminium oxide. LEIS is used as a key analytical tool in assisting with the optimisation of deposition parameters as well as providing insight into reaction mechanisms. This in situ synthesis method is the first documented approach which utilises an intermediate chamber for the production of ALD precursors. The fabricated system is optimised and the molecular intermediate is captured and analysed via nuclear magnetic resonance spectroscopy (NMR). A hopeful outcome of this work is to provide new pathways and tools for the future benefit and advancement of the atomic layer deposition field. The novel approach of in situ synthesis may allow access to novel precursors, which cannot be synthesised by traditional methods and may allow for the deposition of compositionally unique thin films. |
| Exploitation Route | Routes to realise the potential of this research are being explored. The outcomes may prove useful for the semiconductor industry as they provide new synthetic approaches and techniques to fabricate electronic devices. |
| Sectors | Aerospace, Defence and Marine,Chemicals,Electronics,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology |