Porous silicon and its application for micromachining technologies

Meifang Lai

    Research output: ThesisDoctoral Thesis

    275 Downloads (Pure)

    Abstract

    [Truncated abstract] Porous silicon (PS), which exhibits valuable characteristics including photoluminescence, easily tunable refractive index, and large surface area, has gained enormous attention worldwide for innovative photoelectronic applications, such as light-emitting diodes, photodetectors, and sensors. However, only rudimentary PS optical devices and sensors exist at the present stage, due to the environmental and chemical instability of PS. For the next generation of PS devices, patterning of PS after its formation using CMOS-compatible processes to achieve PS devices with homogenous properties, and integration with electronics is desired. In this work, a low-temperature annealing technique is investigated for passivation of PS to achieve environmental and chemical stability. The low-temperature annealed PS (LTA-PS) was obtained by annealing as-fabricated PS in a rapid thermal processor at temperatures as low as 600°C under nitrogen flow. After passivation a very thin layer of SiOxNy was formed on the pore surface, acting as a protective layer against chemical attack and a diffusion barrier against further oxidation. Immersion in HF solution removed the SiOxNy passivation layer, leading to only a 2 % porosity increase. The PS surface is re-terminated with Si-H bonds after HF immersion, enabling it to be reanodised or re-passivated. Compared to as-fabricated PS, LTA-PS has significantly enhanced environmental and chemical stability. It can survive in 1 % KOH (this is a common concentration for alkaline developers in photolithography) for 100 s with an optical thickness change of less than 10 %. The annealing temperature, annealing duration and N2 flow rate were all found to influence the passivation properties. By optimising these conditions, PS annealed at 600°C for 48 minutes with a N2 flow rate of 1000 sccm exhibited excellent chemical resistance to 1 % KOH for at least 10 minutes with negligible film degradation.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Publication statusUnpublished - 2011

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