The purpose of this project is to develop a novel photochemical ALD manufacturing technology. Conventional atomic layer deposition is already widely used in the displays and microelectronics industries. It is a thermo-chemical process where two precursor reagents are pulsed in cycles onto a heated work piece. The combination of the substrate temperature and the chemical reaction energy drive the process forward to deposit the thin film layer by layer. Because the process occurs on the surface, highly uniform and conformal layers can be deposited onto high-aspect ratio or porous materials with ultra-precise thickness control. In this project, we propose to develop a UV photochemical ALD process. The purpose of this is to reduce the dependence of the process on thermal energy. We will use an existing ALD reactor at Liverpool and incorporate into it a switchable UV lamp source. This will be configured so that it can expose the separate gas-phase precursors or on the surface as adsorbates. The wavelength of the output will be tuned to photo-chemically decompose the precursors to form the film. In the second stage of the project we will investigate selective deposition or 'writing' of ALD films. We'll do this using a near field approach with a lithographic plate and secondly by incorporating a TI DLP chip into the optical train just above the work piece. Both of these approaches will enable us to expose adsorbates on the surface selectively and explore the prospect of patterning ALD films. If successful, the project establish the feasibility of a new process technology to extend ALD the other industry sectors, such as roll-to-roll barrier layers; plastic electronics; organic - inorganic PV; biomedical instruments and others.

The rapid growth of computer technology over the last three decades has been largely driven by advances in silicon based materials and processes, which have enabled the development of smaller, faster, lower power transistors. However, we are rapidly approaching fundamental limits of silicon technology and new materials are required to enable future advances. Considerable research has been carried out on developing metal oxides based on materials such as hafnium (Hf) and rare-earth (RE. Such as Gd, La, Nd & Pr) elements, these oxides could be used to replace the native silicon oxide currently used in microelectronics, allowing further device scaling. In contrast to these oxides, little work has been reported about their nitride counterparts, which is perhaps partly due to the challenge associated with their production using conventional-chemistry or thin-film techniques. However, Hf- and RE- nitrides display a wide range of useful electronic and magnetic properties, which are potentially exploitable in a variety of electronic, spintronic and optoelectronic devices. In conventional electronic integrated circuits, nitrides could be used alongside their oxide counterparts, acting as diffusion barriers, nucleation layers or electrical contacts. While in advanced spintronic devices, their magnetic properties could be exploited to enable the production of transistors that operate using the quantum properties of electrons; opening up a new era in computing. In this project, Hf and RE -nitrides will be investigated, using atomic layer deposition (ALD) to produce nitride thin films, and a range of advanced characterisation techniques to study their structural and electrical properties. The ALD process involves exposing a heated surface (usually silicon) to alternating pulses of two complementary precursor gases; one of these is a metal-containing molecule and the other a reactant (such as water or ammonia for oxide or nitride deposition respectively). The precursors are absorbed onto the surface and undergo chemical reactions with the previously absorbed surface molecules, by-products of the reactions are carried away from the surface by a vacuum system leaving a pure oxide, nitride or metal film on the surface. To avoid gas phase reactions between the active gases, inert gas purges are introduced between exposures. As the deposition surface can only accommodate a limited number or precursor molecules, ALD growth is self-limiting, which means that each pair of precursor pulses deposits about one layer of atoms. As a result, ALD allows a very high level of control over films thickness and also produces extremely uniform films (even on high-aspect ratio etched structures), which are essential for advanced microelectronic devices. A number of transition metal-nitrides, most notably titanium and tungsten, have been successfully deposited by ALD. In the first part of this project we will investigate the ALD and properties of Hf-nitride, this material is of technological significance as it complements Hf-oxide, which is expected to be a key material in the production of integrated circuits in the near future. In the second part of this project, we will investigate a number of RE-nitrides, these are expected to have a wide and continuous range of useful electronic and magnetic properties. This ambitious multidisciplinary project will seek to develop a reliable thin film deposition method, which is readily scalable to mass production manufacturing. It will also seek to gain a greater understanding of the physical and electronic properties of these unusual materials.

The rapid growth of the silicon-based microelectronics industry since the late 1980's has fuelled a demand for greater integrated circuit functionality and improved performance at lower cost. This requires an increased circuit density, which has been achieved by a continual reduction, or scaling , in the dimensions of the field effect transistor (FET). Previously amorphous SiO2 and more recently variants of Si-O-N have been exploited in metal-oxide-semiconductor field effect transistor (MOSFET) technology, due to the stable high quality Si-SiO2 interface achievable, and excellent electrical isolation properties. Shrinking of the transistor feature size in each new 'generation' of devices, has forced the gate dielectric thickness to be reduced, to the nanometre-scale level where direct electron tunnelling effects and high leakage currents present serious obstacles to future device reliability. These 'generations' are commonly described by 'nodes' determined by the half pitch between two CMOS gate contact or first metal level. While 90nm node technologies are in industrial production, 65nm node technologies are in advanced status of industrial development and expected to enter in full production in 2007 at the latest. To move to the 45nm node and beyond, the use of materials with a higher dielectric constant (k) (cf. SiO2 derivatives) allows an equivalent capacitance to be achieved in a physically thicker insulating layer, providing reduced leakage currents. This is a multidisciplinary project with the ultimate objective of developing novel liquid injection atomic layer deposition (ALD) process technologies for the manufacture of next generation gate dielectric thin films. The principal aims of the project are therefore to develop an ALD process based on volatile cyclopentadienyl precursors for deposition of hafnium and rare-earth metal oxides, and to assess the physico-chemical and electronic properties of the resulting high-? dielectric films for semiconductor applications.

The goal of this study is to develop new highly volatile CVD precursors to deposit gallium oxide and indium oxide films free from contamination (e.g. C, F) and for a detailed investigation of the gas sensing and TCO (thermally conductive oxide) properties of the resulting films. Gallium oxide (Ga2O3) is considered to be one of the most ideal materials for application as thin-film gas sensors at high temperature. It is thermally stable and an electrical insulator at room temperature but semiconducting above 400 oC. At temperatures above 900 oC the electric conductivity changes depend on the concentration of oxygen, hence the oxygen concentration can be detected. Oxygen gas sensors have practical use in monitoring and controlling oxygen concentrations in exhaust gases of automobiles, as well as waste gases and chemical processes. Above 400 oC Ga2O3 thin-film operates as a surface-control-type sensor to reducing gases, e.g. CO and EtOH. Therefore, it is possible to switch the function of the sensor with temperature. Indium oxide films are both transparent to visible light and conductive (TCO). Dopants (e.g. Sn) can be used to increase the conductivity of the films and to make them more suitable for applications such as in solid-state optoelectronic devices. Group 13 hydrido species possess several notable characteristics that result in them being attractive as precursors to solid-state materials. Firstly, the lack of metal-carbon bonds has the potential to reduce the amount of carbon impurities in the final material and processing temperatures can potentially be reduced due to the thermally frail metal-hydride bonds. Secondly, group 13 hydrides are attractive as precursors as they are considerably more volatile than alkyl derivatives. Thus, a range of novel volatile hydrido-gallium and indium alkoxide complexes as well as heteroleptic alkoxides will be developed. The deposition of Ga2O3 and In2O3 thin-films from the novel precursors synthesised in this programme via low pressure chemical vapour deposition (LP)CVD and aerosol assisted (AA)CVD will be investigated and the gas sensor properties of the films will be assessed. By utilising a wide range of precursors and deposition techniques we will be able to produce different microstructures and develop a correlation landscape between microstructure and gas sensing response. Indium gallium oxide (GaxInyO3) is an exceptional material for TCO applications with absolute transparency that exceed all other oxides / coupled with extremely high charge mobility. Thin-films of GaxInyO3 will be grown using combinatorial atmospheric pressure (AP)CVD and mixed nanoparticulate Ga2O3 inside host In2O3 by AACVD/APCVD from the novel precursors. We have the ability to lay down thin films using a new combinatorial APCVD reactor to make films of graded composition. This new reactor enables upto 400 different compositions to be made on a single plate in one CVD experiment. This is important as it will enable us to rapidly screen composition space in the gallium-indium oxide system and make idealised and optimised compositions for gas sensing and TCO applications. The ability to optimise composition and hence performance in a single CVD experiment would demonstrate the power of the combinatorial technique. Further we have a new reactor design for making indium oxide with embedded nanoparticles- such as gallium oxide. In this system the aerosol flow enters the deposition chamber below the APCVD gas flow, this has the benefit of allowing composite films to be made in which nanoparticles either present or generated in the aerosol droplet are embedded in the APCVD host film. This combined approach will enable us to investigate different nanoparticle densities, sizes and forms and how these effect the gas sensing properties.