Kaliwoh, Never; (2002) Large area low temperature growth of optical and dielectrical materials using excimer lamps. Doctoral thesis (Ph.D.), University College London (United Kingdom).

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Abstract

This research aims to achieve large-area, low-temperature deposition of thin films with high refractive indices, low leakage currents and high dielectric constant for optical and microelectronics applications, using excimer lamps. An efficient system consisting of four excimer lamps filled with xenon producing intense narrowband ultraviolet (UV) radiation at λ-172 nm was constructed and applied to materials' processing. Also, deposition by a new UV assisted Injection Liquid Source (UVILS) developed by JIPELEC and incorporating a krypton chloride (λ-222 nm) lamp is presented. The UVILS technique combines the intense radiation from an excimer lamp with a novel injection liquid source capable of delivering precisely controllable quantities of a liquid precursor into the chemical vapour deposition (CVD) chamber. Silicon dioxide (SiO2), titanium dioxide (TiO2) and composite films of tantalum pentoxide (Ta2O5) doped with TiO2 i.e. (Ta2O5)l-x(TiO2)x were grown and deposited at 400°C and below. A wide range of techniques was employed to characterise these films. Good TiO2 films with refractive indices from 2.20 - 2.54 were grown on crystalline Si and quartz by photo-CVD, with deposition rates around 50 nm/min achieved. The optical band gap of the films. Eg, found to be 3.35eV, is close to the accepted value of 3.5eV for TiO2. (Ta2O5)1-x(TiO2)x films of various compositions were subsequently grown under the same conditions, with a highest dielectric constant value of 51 and band gap energies ranging between 3.2eV and 4.2eV obtained. Films of thickness and refractive indices up to 140 nm and 2.4 respectively were grown by the novel technique of photo-induced sol-gel deposition of TiO2 applied to (Ta2O5)l-x(TiO2)x films. SiO2 films of 1-3 nm thickness were grown on Si by photo-oxidation. The excimer lamp technique requires a low thermal budget, is inexpensive in capital outlay, adaptable due to its simple application and can be easily upscaled to large-areas.

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