| Summary: | 博士 === 國立臺灣大學 === 材料科學與工程學研究所 === 95 === Porous silicon was discovered since 1956, due to its unique optical and electrical properties, it’s still remaining in focus in these decades. The reasons that cause these unique properties are still a puzzle. Someone says that’s because of nano-rod, another thinks it’s due to nano-crystal inside the sponge-like structure. However, there are limitations in the electron microscopy technique and equipment in the past, the morphology of the structure can only observed at low and medium magnification, so there is little information about the structure in nano scale. The researches now a day in porous silicon are for applications, most of them are not focus on its basic structure. Here, the research will using field emission gun TEM equipped with energy dispersion x-ray (EDX) detector and electron energy loss spectroscopy (EELS) detector to analyze its structure in nano-scale. In addition, the purpose of this porous silicon is for non-volatile memory application, we expect there will be nano-crystals formed in the porous silicon layer. So the effect of fabrication process parameters to the morphology and structure is also discussed in this research.
In this research, the porous silicon is fabricated using anodic treatment to the silicon wafer in hydro fluoride solution, followed by rapid thermal oxidation. In this structure, the nanocrystals can be observed with the size in 3~5 nm. For the specimens with different thermal oxidation time, the variation of oxide thickness reaches stable after ten seconds heat treatment, which is about 160 nm. The p+ porous silicon with germanium electroplated has a silicon-germanium crystallized layer with 9 nm thickness at the surface of porous silicon layer. There are V shape voids formed near the interface of porous silicon and silicon in the germanium electroplated p+ porous silicon specimen after 900oC and 1000oC rapid thermal annealing, the side wall of void is parallel to (1 1 1) plans of silicon substrate.
The brief introduction to each chapter of this thesis is descried below:
Chapter One, Abstract: will give a brief introduction to this research and each chapter of this thesis.
Chapter Two, Introduction: will give an introduction to the structure, characteristics and potential of porous silicon, and the need for gate material in non-volatile memory in the future.
Chapter Three, Paper review: Will describe different method and equipment to fabricate porous silicon and the effect of parameters in fabrication process to the morphology of porous silicon. In addition, it also describes several theories about silicon dissolution chemical reactions and pits formation mechanisms.
Chapter Four, Experiment: it divided into two parts; one is the fabrication procedure of porous silicon, another is TEM specimen preparation of semiconductor material.
Chapter Five, Result and discussion: will describe the observation and analysis of porous silicon with different process parameters and heat treatment conditions, which include: observation of porous silicon after anodic treatment, the effect of oxygen ion implantation to porous silicon layer, preparation of single and triple layer porous silicon by changing anodic treatment current, the effect of 1000oC RTO treatment to the structure of porous silicon layer, the effect of 1000oC RTO treatment under hydrogen atmosphere to porous silicon layer, the effect of different anodic treatment parameters to p+ porous silicon layer, the effect of 900oC and 1000oC RTA treatment to germanium electroplated porous silicon layer and the analysis of germanium distribution in porous silicon layer.
Chapter Six, Conclusion: a summary to the research.
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