E-Thesis 332 views
Advanced Functional Coatings for Integrative Semiconductor Materials and Devices / KLAUDIA REJNHARD
Swansea University Author: KLAUDIA REJNHARD
DOI (Published version): 10.23889/SUthesis.64191
Abstract
This Thesis describes a body of work investigating the use of a new thin film deposition technology known as Molecular Vapour Deposition (MVD) for use in semiconductor device fabrication. MVD was first developed in the 1990s, with the first known publications in the early 2000s. It varies from other...
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Swansea, Wales, UK
2023
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| Institution: | Swansea University |
| Degree level: | Doctoral |
| Degree name: | Ph.D |
| Supervisor: | Meredith, Paul. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa64191 |
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| Abstract: |
This Thesis describes a body of work investigating the use of a new thin film deposition technology known as Molecular Vapour Deposition (MVD) for use in semiconductor device fabrication. MVD was first developed in the 1990s, with the first known publications in the early 2000s. It varies from other deposition methods, due to the fact that no carrier gas is required, as it is not a continual flow process; instead, the use of an expansion volume is used to collect vapour prior to use in the main reaction chamber. Stoichiometry is controlled by precursor ratios, deposition temperature and dosing rate. By comparison, ALD is more dependant on precursor/carrier gas flow for controlling stoichiometry. MVD is capable of depositing electrically insulating conducting and semiconducting films in Self-Assembled Monolayer (SAM), Chemical Vapour Deposition (CVD) and Atomic Layer Deposition (ALD) modes. Particular advantageous features of MVD include very precise stoichiometric control, low substrate temperature and the ability to uniformly coat very high aspect ratio structures. The latter feature is becoming ever more important in semiconductor device manufacturing with the progressive evolution of vertical architectures in (for example) high voltage power electronics components, plus the advent of multi-semiconductor integrative platforms. Four target material systems of current and potential high value to semiconductor technology have been studied and deposition processes optimised: i) the standard dielectric Al2O3 in both thermal and plasma enhanced deposition modes (PE-ALD uses oxygen vapours instead of water as a precursor); ii) the semiconductor ZnO which is a common transport and buffer layer in next-generation optoelectronics and n-type channel in thin film transistors; iii) the semiconductor aluminium doped zinc oxide (AZO) which is a promising replacement for indium doped tin oxide (ITO) as a transparent conducting oxide; and finally iv) metallic Pt which is of interest as a selective contact in micro-electronics and vertical architecture semiconductor components, plus as a catalyst, particularly in the nano-domain. The MVD system utilised in this research was a modified version of the SPTS Technologies MVD300 manufacturing tool recently introduced for single-material deposition in the semiconductor industry. The increasing availability of a myriad of metal-organic precursors for CVD and ALD allows a potentially much broader and sophisticated utilisation of MVD and this opportunity underpins and motivates the work described herein. To this end, comprehensive process optimisation and design-of-experiment approaches have been utilised in combination with a range of chemical, structural, electrical and optical characterisation techniques to establish consistent process-structure-property relationships for the chosen target materials. The same precursors can be used for MVD as for ALD, but consideration should be taken for parameters such as temperature, pressure, precursor exposure time, and number of deposition cycles. Key finding presented in this Thesis include: i) 1.5 oxygen-to-aluminium ratio Al2O3 can be deposited at temperatures as low as 100 °C thermally and 60 °C with plasma enhancement – in both cases with text-book refractive indices of 1.63 and state-of-the-art dielectric performance electrically; ii) stoichiometric ZnO layers with refractive index 1.93 can be deposited undoped and the zinc-to-oxygen ratio manipulated with process condition tuning; iii) the Al2O3 and ZnO processes can be combined in a so-called ‘super-cycle’ to deliver state-of-the-art AZO (3% doped) thin films with high average visible transmittance (> 84%) and optimised resistivity of 1.24 ×10-3 Ω·m at a deposition temperature of 125 °C; and iv) fully metallic Pt can be deposited at temperatures as low as 115 °C, and the precise atomic control of MVD could be used as a means to create Pt nanoclusters and transverse the insulator-metal percolation (a process whereby a solid material changes from being electrically non-conductive to conductive) transition in thin Pt films. Temperatures of deposition for each material depend on their reactivity, and this was a consideration for studies within this work. In summary, the technique of Molecular Vapour Deposition has considerable potential to create atomically controlled thin films of metals, semiconductors and dielectrics from an ever-expanding palette of metal-organic precursors. One should consider MVD not only as a semiconductor process tool but also for the creation of layers and structures in nano-electronics, bioelectronics, MEMS, nano-catalysis and even over-the-horizon concepts such as neuromorphic computing. |
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| Keywords: |
MVD, Alumina, AZO, Platinum |
| College: |
Faculty of Science and Engineering |
| Funders: |
EPSRC |