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Atomic Layer Deposition

Deposition of Ultra-Thin Functional Materials

Atomic layer deposition or ALD is a method which does exactly what it says, depositing materials essentially one atomic layer or less at a time. Although it is a relatively slow process, since it is controlled by what are termed self-limiting surface reactions it is capable of highly conformal deposition that follows the often complex contours of the substrate resulting in a layer which is extremely uniform in thickness. ALD is now routinely used in the electronics industry. However, ALD is now also becoming increasingly important for other areas such as solar energy, medical devices and packaging.

 

Four groups at Tyndall contribute to research and development in ALD: the first of these is the Advanced Materials and Surfaces group led by Prof Martyn Pemble. This group possesses enormous expertise in experimental ALD growth and processing and is responsible for the operation of a wide range of ALD systems which include an Applied Materials twin chamber 300 mm system, a Cambridge Nanotech Fiji 200 mm system, a Picosun 150 mm system complete with in-situ ellipsometry and mass spectrometry as well as a range of smaller experimental systems including a near-atmospheric pressure roll-to-roll ALD system designed for proof-of-concept growth on textiles. Most of these systems are also equipped with plasma facilities such that both remote and direct plasma-assisted ALD growth processes can be investigated.

A transmission electron microscopy image of a potential photoelectrochemical water splitting device
A transmission electron microscopy image of a potential photoelectrochemical water splitting device made using ALD at Tyndall, via the US: Ireland project RENEW, which involves partners from Tyndall, Queen’s University Belfast and Stanford University, California.

 

Supported extensively by Applied Materials and Intel and with a global network of academic collaborators, Prof Martyn Pemble and his colleague Dr Ian Povey utilize ALD for advanced CMOS applications including the growth of high-k dielectric materials such as HfO2 and ZrO2 on Si and III/V substrates such as InGaAs and the growth of interconnect materials such as Cu and NiS2. In addition the group studies the growth of doped, transparent conducting oxides such as ZnO and TiO2 for photovoltaic and self-cleaning/antimicrobial applications and the growth of thin film oxides specifically for the passivation of perovskite-based solar cells, together with the growth of VOx materials which have potential applications in smart glazing and Li+ ion battery development. Most recently the group has also been highly active in the use of ALD for the growth of novel photoelectrochemical devices which are capable of splitting water into H2 and O2 and the growth and surface modification of 2D materials such as MoS2, which are being actively developed for application in next generation transistors.

Cross sectional images of metal oxide semiconductor stacks grown by ALD at Tyndall for potential advanced CMOS applications
Cross sectional images of metal oxide semiconductor stacks grown by ALD at Tyndall for potential advanced CMOS applications. A comparison between the top and bottom panels shows that when an Al2O3 interface control layer or ICL of thickness of only ca. 1 nm is grown on the InGaAs substrate that little or no evidence of any native oxide can be seen at the surface of the InGaAs whereas without this layer the native oxide is clearly seen (bottom panel).This work also revealed that the electrical characteristics of the stack were dramatically improved by the presence of the ICL. Taken from Monaghan et al., JVST B, 29, 1, 01A807, 2011

The second group is that of Prof Paul Hurley who are expert in performing the electrical characterisation of the thin layer materials produced by the experimental growth group noted above together with the design of novel device architectures for various applications including advanced CMOS and water-splitting.

 

The third group is that of Dr Aidan Quinn and Dr Micheal Burke, who have very successfully developed routes to the production of high performance MIM capacitor structures using the ALD facilities noted above together with the more routine systems to be found in the Central Fabrication Facility at Tyndall.

 

Finally the group of Dr Simon Elliott performs world-class theoretical studies of ALD processes including DFT calculations which elucidate likely mechanistic pathways plus Monte Carlo simulations of real growth processes themselves.

 

It may be seen that Tyndall is one of the best equipped facilities in Europe for ALD research and development.

 

 

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