多孔矽結構之電子顯微鏡觀察與分析

TEM Observation and Analysis of Porous Silicon

王廷玉(Ting-Yu Wang)

指導教授 ： 楊哲人

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2007年)

https://doi.org/10.6342/NTU.2007.01899

摘要

多孔矽早於1956便被發現，由於其獨特的光學與電學性質，在這數十年來一直受到矚目，對於造成這獨特光、電性質的原因仍是眾說紛紜，有人認為是奈米柱（nano-rod）、有人則認為是海綿狀多孔結構中的奈米晶粒所造成[1]。然而受限於早期電子顯微鏡設備與技術，僅能得知其中、低倍形貌，而無法得知其奈米尺度之結構，現今多孔矽研究則以其應用為主，對其基本結構則少有著墨。因此，此研究中將以場發射穿透式電子顯微鏡輔以電子能量散佈偵測器（EDX）及電子能量損失偵測器（EELS）來探討其奈米尺度結構。此外，在多孔矽製備上則是以非揮發性記憶體（non-volatile memory）的應用為目標，期望在多孔矽層內形成奈米晶粒，因此在此研究中亦探討多孔矽製程參數對其形貌與結構之影響。

在此研究中，多孔矽膜的製備是將矽基材於氟化氫溶液中進行陽極處理，再進行快速熱氧化而得到。此結構中可得到尺寸約為3~5 nm的奈米晶粒。在改變快速熱氧化時間的實驗中，得知十秒的熱處理時間即可使氧化層厚度達到穩定，約為160 nm。經鍺電鍍後之P+多孔隙膜，，於表面會形成一層約9 nm的矽鍺結晶層。而於900oC與1000oC回火過後鍍鍺多孔矽膜於多孔矽與矽基材介面處會產生V形孔洞，其側壁平行於矽基材(1 1 1)族平面。

在本文中：
第一章、簡介：將對本研究作簡介並對各章節作概要述說
第二章、前言：將對多孔矽結構與特性及其潛力以及未來非揮發性記憶體對閘極材料的需求作介紹
第三章、文獻回顧：將對說明不同多孔矽製作設備、程序以及至程參數條件對多孔矽形貌的影響。另整理了對於矽溶解化學反應與孔洞形成機制的理論。
第四章、實驗：分為兩部分，一為多孔矽試片製備流程；另一則是半導體TEM試片製備方法。
第五章、結果與討論：分別對於不同製程參數及及熱處理條件下的多孔矽進行觀察與分析，其中包含：多孔矽原始形貌觀察、氧離子佈植對多孔矽之影響、以改變陽極處理電流製備多孔矽單層與三層結構、不同1000 oC RTO熱處理時間對多孔矽層結構的影響、於氫氣氛下1000 oC快速熱回火對多孔矽層結構的影響、不同陽極處理條件對p+型多孔矽結構之影響、RTA熱處理對鍍鍺多孔隙膜之影響、900℃與1000℃RTA熱處理對鍍鍺多孔隙膜之影響、多孔矽膜中之鍺元素分佈之影響以及多孔矽表面之緻密結晶層。
第六章、結論：對於以上研究作一歸納總結。

關鍵字

多孔矽 ； 穿透式電子顯微鏡

並列摘要

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.

並列關鍵字

porous silicon ； TEM

參考文獻

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