生成金屬鈦矽化物奈米結構之研究

Investigation of the formation of titanium silicide nanostructures on silicon

許宏彰(Hung-Chang Hsu)

指導教授 ： 陳力俊

國立清華大學/工學院/材料科學工程學系/博士(2007年)

摘要

近年來一維奈米結構受到很多研究人員的注意，主要是因為其特殊的性質以及將來可能在微電子與光電元件方面的應用。本研究利用掃瞄穿隧式電子顯微鏡（STM）、原子力顯微鏡（AFM）、穿透式電子顯微鏡（TEM）以及臨場超高真空穿透式電子顯微鏡（in situ UHV-TEM）研究金屬鈦矽化物在矽基材上的奈米結構與成長機制。
在Si(111)基材上，當基材溫度為600~700度時，鈦矽化物會生成C49-TiSi2結晶相的奈米線與微粒兩種奈米結構，而當基材溫度升高至800度時，鈦矽化物會轉變成微粒結構。這些鈦矽化物奈米線在矽基材上沿著Si<2-20>方向成長，並且存在著C49-TiSi2(200)//Si(2-20)的晶面關係。
藉由in situ UHV-TEM的觀察，進一步瞭解鈦矽化物奈米線在Si(111)基材上的相互作用模式。當奈米線在相同方向成長並接觸時，最後會結合在一起；但若奈米線在不同方向成長並接觸時，則會產生奈米線相互併吞或收縮的結果。根據此觀察結果，利用某些特殊基材，例如Si(110)，可成長單一方向且高長寬比( high aspect ratio)的鈦矽化物奈米線。
在Si(110)基材上，C49-TiSi2結晶相奈米線的尺寸與密度會受到基材溫度、鍍膜速率以及鍍膜時間的影響，因此藉由調整這些參數，可進一步控制奈米線的尺寸與長寬比。此外，經由計算奈米線密度與基材溫度之間的關係式，鈦矽化物奈米線的生成活化能約為0.75 eV。
鈦矽化物在Si(001)基材上，當基材溫度為600度時，會生成微粒結構，而當基材溫度升高至700度時，則會生成O-Ti5Si4結晶相奈米線結構並沿著兩個互相垂直的Si<220>方向排列，這些奈米線的生成是由於長軸方向與短軸方向上不對稱的晶格匹配程度所造成。

關鍵字

矽化物 ； 奈米線 ； 掃瞄穿隧式電子顯微鏡 ； 臨場觀測穿透式電子顯微鏡

並列摘要

The growth mechanism and morphology of titanium silicide nanostructures on Si substrate have been investigated by scanning tunneling microscope (STM), atomic force microscope (AFM), transmission electron microscope (TEM), and in situ ultrahigh-vacuum TEM (UHV-TEM).
The growth of titanium silicide was investigated in sub-monolayer Ti deposited on Si(111). The formation of nanowire (NW) and cluster structures was observed for 600 and 700 °C deposited samples. In sample heated to 800 °C, titanium silicide structures transformed to clusters. C49-TiSi2 NWs were found to orient along three equivalent Si <2-20> directions with C49-TiSi2(200)//Si(2-20). Deposition of sub-monolayer Ti at a high temperature was found to contribute to the lowering of the formation temperature of C49-TiSi2. The lowering of C49-TiSi2 growth temperature on heated substrate is attributed to smaller lattice mismatch between C49-TiSi2(200) and Si(2-20).
Understanding the growth mechanism of NWs is essential for their successful implementation in advanced devices applications. In situ UHV-TEM has been applied to elucidate the interaction mechanisms of TiSi2 NWs on Si(111) substrate. Two phenomena were observed: merging of the two NWs in the same direction, and collapse of one NW on a competing NW in different directions when they meet at the ends. On the other hand, as one NW encounters the midsection of the other NW in different direction, it receded in favor of the bulging of the other NW at the midsection. The crucial information has been fruitfully exploited to grow long and high-aspect-ratio titanium silicide NWs on Si(110) since the NWs grow only in the [2-20] direction.
The formation of titanium silicide NWs was investigated on Si(110) samples at 600-700 °C. From STM and AFM observation, the average length and aspect ratio of NWs increased with substrate temperatures. These NWs were oriented along one Si(2-20) direction with C49-TiSi2(200)//Si(2-20). The density of NWs is dependent of substrate temperatures and the activation energy E* for titanium silicide NW growth is 0.75 ± 0.1 eV. The growth of titanium silicide NWs was found to be significantly affected by the deposition rate and growth time.
The self-assembled titanium silicide NWs on Si(001) substrate were investigated. Titanium silicides in the 600 °C deposited sample are of islands nanostructure and form NW shape in the 700 °C deposited sample. These titanium silicide NWs are aligned in two perpendicular <220> directions of Si substrate with large aspect ratio. From the analysis of TEM, the NWs were identified to be of O-Ti5Si4 phase with the epitaxial relationships of O-Ti5Si4[400]//Si[220] and O-Ti5Si4(034)//Si(001) and resulted from the anisotropic lattice mismatches that is good in the long axis and poor in the short axis of the NW.

並列關鍵字

silicide ； nanowire ； STM ； in situ TEM

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